WBBSE Solutions For Class 9 Physical Science Chapter 4 Matter Acids Bases And Salts

Chapter 4 Matter Acids Bases And Salts Topic A Concept Of Acid And Bases Synopsis

  1. According to Arrhenius theory of electrolytic dissociation, an acid is a hydrogen-containing compound which dissociates in aqueous solution to produce H+ ion (or H3O+ ion) as the only cation. On the other hand, compounds that yield OH ions as the only anion in their aqueous solutions are called bases.
  2. Acids like H2SO4, HCI, HNO3 and bases like NaOH, KOH find important applications in different industries.
  3. Metals do not produce hydrogen on reacting with cold and very dilute HNO3. Only Mg and Mn can displace hydrogen from cold and very dilute nitric acid.
  4. Hydrochloric acid is identified by using aqueous solution of silver nitrate. Aqueous solution of barium chloride is used to identify sulphuric acid. Nitric acid is identified by the ring test.
  5. Strong acids and strong bases are highly corrosive in nature. So, proper precautionary measures are adopted while using them.
  6. When concentrated nitric acid is refluxed With small amount of starch, a yellow-coloured solution of nitric acid containing different oxides of nitrogen is obtained. It is called fuming nitric acid.

Chapter 4 Matter Acids Bases And Salts Topic A Concept Of Acid And Bases Short And Long Answer Type Questions

Question 1. Define acids in the light of Arrhenius’s theory of electrolytic dissociation.

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Answer:

Arrhenius’s Theory Of Electrolytic Dissociation :-

According to Arrhenius theory of electrolytic dissociation, an acid is defined as a hydrogen-containing compound that dissociates in; water to produce H+ ions (or H3O+ ions) as the only cation.

For example, HCI ionises in water to produce H+ (or H3O+) ions as the only cation. Hence, HCI is an acid.

\(\mathrm{HCl} \rightarrow \mathrm{H}^{+}+\mathrm{Cl}^{-} ; \mathrm{H}^{+}+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{H}_3 \mathrm{O}^{+}\)


Question 2. Mention the general properties of acids.

Answer:

General Properties Of Acids Are

  1. Acids are ionised in aqueous solution forming H ion (H3O ion actually) and thus can conduct electricity.
  2. Acids are sour in taste.
  3. Acids turn blue litmus paper red.
  4. Acids generally produce hydrogen gas in reaction with metal.
  5. Acids generally produce carbon dioxide in reaction with carbonates and bicarbonates.
  6. Acids produce salt and water in reaction with alkali.

Question 3. Why do free H+ Ions not exist in water or aqueous solution?

Answer:

H+ ions combine with electronegative oxygen atoms in water to produce hydroxonium or hydronium ions (H3O+). So, free H+ ions do not exist in water or aqueous solution.

Question 4. What are inorganic or mineral acids and give some examples.

Answer:

Inorganic Acids :

Acids which are obtained from minerals or produced from inorganic substances are known as mineral acids. Hydrochloric acid (HCI), sulphuric acid (H2SO4), nitric acid (HNO3) are some examples of mineral acids.

Question 5. What are organic acids and give some examples.

Answer:

Organic Acids :

Acids (containing carbon atoms) which are obtained from plants or animals are called organic acids. For example, formic acid is found in ant venom, lemon contains citric acid, lactic acid is present in curd etc.

Question 6. What is meant by ionisation of an acid in aqueous solution and give example.

Answer:

Ionisation Of An Acid In Aqueous Solution

In aqueous solution, an acid dissociates to form H+ ions which are unstable in nature. So these ions combine with water molecules to form hydronium ions (H3O+). This decomposition of an acid in its aqueous solution is known as the ionisation of an acid.

\(\mathrm{HCl}(a q)+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{H}_3 \mathrm{O}^{+}(a q)+\mathrm{Cl}^{-}(a q)\)


Question 7. What are strong acids and give examples.

Answer:

Strong Acids :

Acids which almost completely dissociate in aqueous solution to produce large amount of H3O+ ions are called strong acids. Some examples are hydrochloric acid (HCI), sulphuric acid (H2SO4), nitric acid (HNO3), perchloric acid (HCIO4) etc.

Question 8. What are weak acids and give examples.

Answer:

Weak Acids :

Acids which partially dissociate in aqueous solution to produce small amount of H3O+ ions and most of the molecules remain undissociated in the solution are called weak acids. Some examples are acetic acid (CH3COOH), carbonic acid (H2CO3), citric acid etc.

Question 9. Give definition of a base according to Arrhenius’s theory.

Answer:

Arrhenius’s Theory :

According to Arrhenius theory, a base can be defined as a compound (mainly the metal oxides and metal hydroxides) which on dissociating in water produces hydroxyl ions (OH) as the only anion.

Na2O, NaOH, CaO are some examples of bases.

Question 10. Mention the general properties of bases.

Answer:

General Properties Of Bases Are :

  1. Bases form OHe ion as anion when they are dissolved in water.
  2. Bases taste bitter and are generally soapy in nature.
  3. Bases turn red litmus paper blue.
  4. Bases form salt and water in reaction with acids.

Question 11. NaOH is a strong base but NH4OH is a weak base. Explain.

Answer:

Difference Between Strong And Weak Base :

NaOH dissociates completely into Na and OHΘ ions in aqueous solution.

⇒ \(\mathrm{NaOH} \rightleftharpoons \mathrm{Na}^{\oplus}+\mathrm{OH}^{\ominus}\)

But NH4OH dissociates partially into NH and OHΘ ion in aqueous solution.

⇒ \(\mathrm{NH}_4 \mathrm{OH} \rightleftharpoons \mathrm{NH}_4^{\oplus}+\mathrm{OH}^{\ominus}\)

Depending of the nature of ionic dissociation in their respective aqueous solutions, NaOH acts as a strong base and NH4OH acts as a weak base.

Question 12. Mention the limitations of Arrhenius acid-base concept.

Answer:

Limitations Of Arrhenius Acid-Base Concept :

The limitations of Arrhenius acid-base concept are as follows

1. According to this concept, an acid or a base is defined on the basis of their dissociation in aqueous solutions. Thus, the concept is limited to aqueous medium only. It cannot explain the acidic or basic property of compounds in solvents other than water (non-aqueous solvents) like liquid ammonia, benzene etc.

2. According to this concept, a base must yield OH ions in aqueous medium. Thus, the theory fails to explain the basic nature of compounds like ammonia (NH3), methyl amine (CH3NH2), aniline (C6H5NH2) etc. Similarly acidic nature of compounds like BF3 or AICI3 cannot be explained by this theory as these compounds do not produce H+ ions in aqueous medium.

Question 13. All acids are hydrogen-containing compounds, but all hydrogen-containing compounds are not acids—justify the statement with example.

Answer:

All Acids Are Hydrogen-Containing Compounds, But All Hydrogen-Containing Compounds Are Not Acids :

According to Arrhenius theory, an acid must contain H-atom. However, a compound containing hydrogen will be called an acid only if it has the following properties

  1. It will dissociate in aqueous solution to produce H3O+ (hydroxonium) ions.
  2. It will produce hydrogen gas on reacting with metals.
  3. It will react with a base or an alkali to produce salt and water.
  4. Its aqueous solution will turn blue litmus red. However there are compounds containing hydrogen, which do not exhibit these properties.

For Example

  1. Compounds like PH3, NH3, CH4, sugar (C12H22O11) do not H3O+ ions in aqueous solution. Neither do they react with metals to produce hydrogen gas nor do they react with bases to form salt and water.
  2. Sodium reacts with H2O to produce hydrogen gas but the reaction produces NaOH instead of a salt.
  3. Al, Zn etc. react with compounds like sodium hydroxide, potassium hydroxide etc. to produce hydrogen gas but these compounds do not yield H3O+ ions in their aqueous solution. So, these compounds are not acids.

Question 14. Why are CaH2 and CH4 not acids?

Answer:

CaH2 and CH4 Are Cannot Be Termed As An Acids Because :

CaH2 produces H ion or hydride ion. That is why it cannot be termed as an acid.

\(\mathrm{CaH}_2 \rightarrow \mathrm{Ca}^{2+}+2 \mathrm{H}^{\ominus}\)

CH4 is a covalent compound and cannot form H ion in aqueous solution. Hence CH4 cannot be termed as acid.

Question 15. All alkalis are bases, but all bases are not alkalis—explain.

Answer:

All Alkalis Are Bases, But All Bases Are Not Alkalis :

A base dissolves in water to form an alkali.

However, all bases are not soluble in water and these bases do not form alkalis. Thus, all alkalis are bases, but bases insoluble in water are not alkalis.

For example, Na2O is a base. It dissolves in water to form NaOH. Sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide [Ca(OH)2] dissolve in water to give OH ions. So these are alkalis.

⇒ \(\mathrm{NaOH} \rightarrow \mathrm{Na}^{+}+\mathrm{OH}^{-} ; \mathrm{KOH} \rightarrow \mathrm{K}^{+}+\mathrm{OH}^{-}\)

⇒ \(\mathrm{Ca}(\mathrm{OH})_2 \rightarrow \mathrm{Ca}^{2+}+2 \mathrm{OH}^{-}\)

On the other hand, aluminium hydroxide [AI(OH)3], zinc hydroxide [Zn(OH)2], ferric hydroxide [Fe(OH)3] etc. react with acids to form salt and water. So they are bases. However, as they are insoluble in water, they cannot be called alkalis.

Question 16. Sodium hydroxide (NaOH) is a base, but  CIOH is an acid. Why?

Answer:

Sodium Hydroxide (NaOH) Is A Base, But  CIOH Is An Acid Because :

NaOH dissociates in water to produce Na+ and OH ions. As it yields OH ions in water, it is called a base. On the other hand, CIOH dissociates in water to give CIO and H+ ions.

H+ ions further combine with water molecules to form H3O+ ions. As it produces H3O+ ions in aqueous solution, it is an acid.

Question 17. State whether AI(OH)3 is a base or an alkali. Justify your choice.

Answer:

Aluminium Hydroxide AI(OH)3 Is Not An Alkali.

Water soluble metal hydroxides are known as alkalis. Aluminium hydroxide [AI(OH)3] is a base as it reacts with acid to produce salt and water but it is insoluble in water. So, aluminium hydroxide is not an alkali.

Question 18. Give an example of a reaction where two gases react to form a solid.

Answer:

Example Of A Reaction Where Two Gases React To Form A Solid :

Ammonia gas reacts with hydrogen chloride gas to form fine particles of solid ammonium chloride which floats in air forming white fumes.

Equation: \(\mathrm{NH}_3+\mathrm{HCl} \rightarrow \mathrm{NH}_4 \mathrm{Cl}\)

Question 19. Write down equations for the reaction of HCI with NaOH, Mg(OH)2 and AI(OH)3 respectively.

Answer:

Equations For The Reaction Of HCI With NaOH, Mg(OH)2 And AI(OH)3 Respectively : 

HCI forms corresponding salts and water in reaction with the mentioned bases:

⇒ \(\mathrm{NaOH}+\mathrm{HCl} \rightarrow \mathrm{NaCl}+\mathrm{H}_2 \mathrm{O}\)

⇒ \(\mathrm{Mg}(\mathrm{OH})_2+2 \mathrm{HCl} \rightarrow \mathrm{MgCl}_2+2 \mathrm{H}_2 \mathrm{O}\)

∴ \(\mathrm{Al}(\mathrm{OH})_3+3 \mathrm{HCl} \rightarrow \mathrm{AlCl}_3+3 \mathrm{H}_2 \mathrm{O}\)

Question 20. Give examples of chemical reactions of hydrochloric acid with carbonates and bicarbonate compounds.

Answer:

Chemical Reactions Of Hydrochloric Acid With Carbonates And Bicarbonate Compounds :-

Hydrochloric acid reacts with carbonate and bicarbonate compounds to liberate carbon dioxide and produce corresponding chloride salts.

⇒ \(\mathrm{Na}_2 \mathrm{CO}_3+2 \mathrm{HCl} \rightarrow 2 \mathrm{NaCl}+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2 \uparrow\)

⇒ \(\mathrm{NaHCO}_3+\mathrm{HCl} \rightarrow \mathrm{NaCl}+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2 \uparrow\)

Question 21. Under what condition does Cu react with HCI? Give equation.

Answer:

Condition For The Reaction Of Cu With HCI

Copper slowly reacts with hot and concentrated HCI in the presence of air or oxygen O2(g) to produce cupric chloride (CuCI2) and water.

WBBSE Solutions For Class 9 Physical Science Chapter 4 Topic A Concept Of Acid And Bases

Question 22. Give an example of the reducing property of hydrochloric acid (HCI).

Answer:

Reducing Property Of Hydrochloric Acid (HCI) :

Hydrochloric acid reduces manganese dioxide (MnO2) to manganous chloride (MnCI2) and itself gets oxidised to evolve greenish-yellow chlorine gas.

⇒ \(\mathrm{MnO}_2+4 \mathrm{HCl} \rightarrow \mathrm{MnCl}_2+\mathrm{Cl}_2 \uparrow+2 \mathrm{H}_2 \mathrm{O}\)

Question 23. How will you identify hydrochloric acid? Give corresponding equation.

Answer:

Identification Of Hydrochloric Acid:

When silver nitrate (AgNO3) solution is added to an aqueous solution of hydrochloric acid (HCI), a curdy white precipitate of silver chloride (AgCI) is obtained. The precipitate is insoluble in nitric acid but dissolves readily in excess ammonium hydroxide (NH4OH) solution.

⇒ \(\mathrm{AgNO}_3+\mathrm{HCl} \rightarrow \mathrm{AgCl} \downarrow+\mathrm{HNO}_3
(white ppt.)\)

WBBSE Solutions For Class 9 Physical Science Chapter 4 Topic A Concept Of Acid And Bases Hydrochloric Acid

Question 24. Mention some uses of hydrochloric acid in industries.

Answer:

Uses Of Hydrochloric Acid In Industries.

Some important uses of hydrochloric acid are as follows

  1. In the preparation of chlorine and different metal chlorides.
  2. Preparation of aqua regia and glucose (from starch) and in removing scales from boilers
  3. In dye industries, tanneries, pharmaceutical industries and during galvanisation and tinplating of iron.

Question 25. What happens when carbonate and bicarbonate compounds react with nitric acid (HNO3)? Give equations.

Answer:

Nitric acid reacts with carbonate and bicarbonate compounds to liberate carbon dioxide and produce corresponding nitrate salts.

\(\mathrm{Na}_2 \mathrm{CO}_3+2 \mathrm{HNO}_3 \rightarrow 2 \mathrm{NaNO}_3+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2 \uparrow\) \(\mathrm{NaHCO}_3+\mathrm{HNO}_3\rightarrow \mathrm{NaNO}_3+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2 \uparrow\)

Question 26. Write with equation what happens when copper turnings are heated with hot and concentrated nitric acid.

Answer:

When copper turnings are heated with hot and concentrated nitric acid, brown fumes of nitrogen dioxide (NO2) gas is evolved. Copper is oxidised by nitric acid to copper nitrate [Cu(NO3)2] which makes the solution bluish-green in colour.

\(\mathrm{Cu}(s)+4 \mathrm{HNO}_3(a q) \longrightarrow \mathrm{Cu}\left(\mathrm{NO}_3\right)_2(a q)+2 \mathrm{NO}_2(g) \uparrow+2 \mathrm{H}_2 \mathrm{O}(l)\)

Question 27. Give An example of the oxidising property of nitric acid.

Answer:

Example Of The Oxidising Property Of Nitric Acid :

Hot and concentrated nitric acid oxidises metallic zinc to zinc nitrate [Zn(NO3)2] and itself gets reduced to nitrogen dioxide.

\(\mathrm{Zn}+4 \mathrm{HNO}_3 \rightarrow \mathrm{Zn}\left(\mathrm{NO}_3\right)_2+2 \mathrm{NO}_2 \uparrow+2 \mathrm{H}_2 \mathrm{O}\)

Question 28. Which acid is termed as ‘aqua fortis’ or ‘strong water’? How can hydrogen be produced form that acid?

Answer:

  1. Nitric acid is termed as ‘aqua fortis’.
  2. In the reaction with Magnesium (Mg), very dilute (1%) nitric acid produces hydrogen.

⇒ \(\mathrm{Mg}+2 \mathrm{HNO}_3 \rightarrow \mathrm{Mg}\left(\mathrm{NO}_3\right)_2+\mathrm{H}_2 \uparrow\)

Question 29. What is fuming nitric acid?

Answer:

Fuming Nitric Acid :

When concentrated nitric acid (HNO3) is refluxed with starch, a brownish-yellow solution is obtained containing different oxides of nitrogen (mainly NO2) dissolved in it. This solution is called fuming nitric acid. It has been so named because the dissolved NO2 continuously comes out from the solution as brown fumes.

Question 30. Why does concentrated nitric acid turn yellow in presence of sunlight?

Answer:

In presence of sunlight, concentrated nitric acid decomposes to form brown-coloured NO2 gas. This gas dissolves in nitric acid and turns the solution yellow.

⇒ \(4 \mathrm{HNO}_3 \rightarrow 4 \mathrm{NO}_2 \uparrow+2 \mathrm{H}_2 \mathrm{O}+\mathrm{O}_2 \uparrow\)

Question 31. Prove that oxygen is present in nitric acid.

Answer:

Oxygen Is Present In Nitric Acid :

When concentrated HNO3 is added drop-wise on red-hot pumice stone, a brown gas mixture evolves. When this gas mixture in passed through a ‘Ll’ tube dipped in freezing mixture, a colourless gas is evolved through ‘U’ tube which ignites a flameless burning stick.

The colourless gas gets absorbed by the alkaline potassium pyrogallate solution and turns the colour of the solution brown. So the gas is oxygen which comes from nitric acid.

\(4 \mathrm{HNO}_3 \rightarrow 2 \mathrm{H}_2 \mathrm{O}+\mathrm{NO}_2+\mathrm{O}_2\)

This reaction proves the presence of oxygen in nitric acid.

Question 32. Concentrated nitric acid can not be kept in copper vessel but the same can be kept in aluminium vessel. Why?

Answer:

Nitric acid produces brown fumes of nitrogen dioxide and copper nitrate if it is kept in a copper vessel.

⇒ \(\mathrm{Cu}+4 \mathrm{HNO}_3 \rightarrow \mathrm{Cu}\left(\mathrm{NO}_3\right)_2+2 \mathrm{NO}_2+2 \mathrm{H}_2 \mathrm{O}\)

That is why concentrated HNO3 can not be kept in copper vessel.

If concentrated nitric acid is kept in an aluminium vessel, nitric acid reacts with aluminium to form aluminium oxide. This aluminium oxide forms a thin layer which is insoluble in HNO3.

So the concentrated HNO3 can not come in contact with aluminium furthermore. That is why concentrated HNO3 can be kept in aluminium vessel.

Question 33. Describe ring test performed for identification of nitric acid. Give relevant equations.

Answer:

Ring Test Performed For Identification Of Nitric Acid :

A sample of the given solution is taken in a test tube and freshly prepared ferrous sulphate (FeSO4) solution is added to it. Then the solution is cooled and concentrated H2SO4 is gradually poured into the solution along the side of the test tube.

Sulphuric add being denser moves down and a brown ring is formed at the junction of the two liquid layers (acid + solution consisting of FeSO4 and sample). This test confirms the presence of nitric acid or any other nitrate salt.

HNO3 reacts with FeSO4 in the presence of concentrated H2SO4 to produce nitric oxide (NO). The formed nitric acid then combines with FeSO4 to form a complex [Fe(H2O)5NO]SO4 [pentaaquanitrosyliron (II) sulphate] which is responsible for the formation of the brown ring.

⇒ \(2 \mathrm{HNO}_3+3 \mathrm{H}_2 \mathrm{SO}_4+6 \mathrm{FeSO}_4 \longrightarrow 3 \mathrm{Fe}_2\left(\mathrm{SO}_4\right)_3+2 \mathrm{NO}+4 \mathrm{H}_2 \mathrm{O}\)

⇒ \(\mathrm{FeSO}_4+6 \mathrm{H}_2 \mathrm{O} \rightarrow\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right] \mathrm{SO}_4\)

⇒ \({\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right] \mathrm{SO}_4+\mathrm{NO} \longrightarrow}{\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_5 \mathrm{NO}_3\right] \mathrm{SO}_4+\mathrm{H}_2 \mathrm{O}}\)

WBBSE Solutions For Class 9 Physical Science Chapter 4 Topic A Concept Of Acid And Bases Ring Test Formed For Identification Nitric Acid

Question 34. Why is freshly prepared ferrous sulphate solution used in the ring test for the identification of nitric acid?

Answer:

The Reason For Freshly Prepared Ferrous Sulphate Solution Used In The Ring Test For The Identification Of Nitric Acid Is : 

In the presence of atmospheric oxygen, ferrous sulphate solution is rapidly oxidised to ferric sulphate. Ferric sulphate cannot form any complex with NO.

Hence, ferrous sulphate solution stored in laboratory cannot form the brown ring under the given reaction conditions. Thus, freshly prepared ferrous sulphate is used in the ring test for identification of nitric acid.

Question 35. The brown ring formed in the ring test disappears when the test tube is shaken. Why?

Answer:

The Brown Ring Formed In The Ring Test Disappears When The Test Tube Is Shaken Because:

When the test tube is shaken, concentrated H2SO4 combines with water and evolves large amount of heat which decomposes the complex compound, [Fe(H2O)5NO]SO4 and liberates nitric oxide (NO) gas.

NO comes out as bubbles from the test tube. As the complex responsible for ring formation decomposes, the brown ring disappears.

Question 36. Mention some uses of nitric acid in industries.

Answer:

Uses Of Nitric Acid In Industries:

Some important uses of nitric acid in industries are as follows

  1. It is used in the manufacture of different explosives like nitroglycerine, picric acid, TNT (trinitrotoluene) etc.
  2. It is used in the production of celluloids, synthetic colours, synthetic silk etc.
  3. HNO3 is used in the production of electrical cells, nitrate salts, fertilisers, aqua regia etc. with a glass rod. As a result, the produced heat is evenly distributed, thereby reducing the chance of any accident.

Question 37. What happens when carbonate and bicarbonate compounds react with sulphuric acid (H2SO4)? Give equations.

Answer:

Carbonate and bicarbonate compounds react with sulphuric acid to liberate carbon dioxide and produce corresponding sulphate salts.

⇒ \(\mathrm{Na}_2 \mathrm{CO}_3+\mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{Na}_2 \mathrm{SO}_4+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2 \uparrow\)

⇒ \(\mathrm{NaHCO}_3+\mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{NaHSO}_4+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2 \uparrow\)

Question 38. Give an example of the oxidising property of sulphuric acid.

Answer:

Example Of The Oxidising Property Of Sulphuric Acid:

Hot and concentrated sulphuric acid oxidises metallic zinc to zinc sulphate (ZnSO4) and itself gets reduced to sulphur dioxide.

⇒ \(\mathrm{Zn}+2 \mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{ZnSO}_4+\mathrm{SO}_2 \uparrow+2 \mathrm{H}_2 \mathrm{O}\)

Question 39. Give suitable conditions and equations of the reaction between copper and sulphuric acid.

Answer:

Copper reacts with hot and concentrated sulphuric acid to produce blue-coloured copper sulphate and sulphur dioxide gas which has a smell of burnt sulphur.

⇒ \(\mathrm{Cu}(s)+2 \mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{CuSO}_4(a q)+\mathrm{SO}_2 \uparrow+2 \mathrm{H}_2 \mathrm{O}(l)\)

Question 40. Give an example of hygroscopic property of concentrated sulfuric acid.

Answer:

When cone. H2SO4 is added to blue vitriol crystals, white powder of anhydrous copper sulfate is formed. This is an example of the hygroscopic property of cone. H2SO4 .

⇒ \(\mathrm{CuSO}_4 \cdot 5 \mathrm{H}_2 \mathrm{O} \stackrel{\text { Conc. } \mathrm{H}_2 \mathrm{SO}_4}{-5 \mathrm{H}_2 \mathrm{O}} \mathrm{CuSO}_4\)

Question 41. What happens when a few drops of cone. H2SO4 are added to sugar?

Answer:

Sugar turns to black carbon when a few drops of cone. H2SO4 are added to it.

⇒ \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11} \frac{\text { Conc. } \mathrm{H}_2 \mathrm{SO}_4}{-11 \mathrm{H}_2 \mathrm{O}} 12 \mathrm{C} \text { (black) }\)

 

WBBSE Solutions For Class 9 Physical Science Chapter 4 Topic A Concept Of Acid And Bases Metal Activity Series

Question 42. Fe reacts with dilute H2SO4 to liberate hydrogen, but Cu does not—explain.

Answer:

Only metals present above hydrogen in the metal activity series can replace hydrogen from a dilute acid. Iron is placed above hydrogen while copper is placed below hydrogen in the metal activity series.

So iron reacts with dilute sulphuric acid to liberate hydrogen but copper is not able to do so. It must be noted that, copper does not react with dilute sulphuric acid but it is oxidised by hot and concentrated sulphuric acid.

Question 43. How will you identify sulphuric acid? Give equation.

Answer:

When barium chloride (BaCI2) solution is added to an aqueous solution of sulphuric acid (H2SO4), white barium sulphate (BaSO4) is precipitated which is insoluble in hydrochloric acid (HCI) or nitric acid (HNO3).

⇒ \(\mathrm{H}_2 \mathrm{SO}_4+\mathrm{BaCl}_2 \rightarrow \mathrm{BaSO}_4 \downarrow+2 \mathrm{HCl}\)

Question 44. Three bottles contain equal volumes of concentrated HCI, concentrated HNO3 and concentrated H2SO4 How will you identify the bottle containing H2SOwithout conducting any chemical test?

Answer:

The specific gravity of concentrated H2SO4 is much greater than that of concentrated HCI and concentrated HNO3. Hence, the bottle which is heaviest contains concentrated H2SO4.

Question 45. What is oleum?

Answer:

Oleum:

When an excess amount of SO3 gas is passed through 98% cone. H2SO4, the gas gets absorbed by the acid and an oily liquid substance of formula H2S2O3 is formed. This substance is termed as oleum.

⇒ \(\mathrm{H}_2 \mathrm{SO}_4+\mathrm{SO}_3 \rightarrow \mathrm{H}_2 \mathrm{~S}_2 \mathrm{O}_7\)

Question 46. Prove the presence of hydrogen in sulphuric acid.

Answer:

Presence Of Hydrogen In Sulphuric Acid :

At room temperature, dil. H2SO4 and granulated zinc react to produce a colourless, odourless gas in which an ignited splint is extinguished and the gas burns with blue flame in air forming a colourless liquid.

This colourless liquid turns the white anhydrous copper sulphate blue. So this colourless liquid is water which was formed by the combustion of the colourless, odourless gas.

Therefore, the said gas is hydrogen which was formed by the reaction of granulated zinc and dil. H2SO4. Hence the pressence of hydrogen in H2SO4 is proved.

⇒ \(\mathrm{Zn}+\mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{ZnSO}_4+\mathrm{H}_2\)

Question 47. Mention some uses of sulphuric acid in industries.

Answer:

Some important uses of sulphuric acid are as follows

  1. H2SO4is used in the preparation of inorganic acids like hydrochloric acid and nitric acid.
  2. H2SO4 is used in the preparation of fertilisers like super phosphate, ammonium sulphate.
  3. Sulphuric acid finds application in the production of alum, glucose, ethers, alcohols, dyes, explosives etc.
  4. It is used for processes such as, petroleum refining and galvanisation.
  5. H2SO4 is also used in lead storage batteries, extraction of metals and manufacture of films and synthetic silk.

Question 48. Acids are not stored in metal containers. Explain.

Answer:

Metals placed above hydrogen in the activity series react with acids to produce salts and hydrogen gas. So, acids cannot be kept in contact with active metals. For example, Fe reacts with dilute H2SO4 to produce FeSO4 salt and hydrogen gas.

Question 49. Nowadays, the contept of nascent hydrogen is considered to be obsolete— explain with an example.

Answer:

When hydrogen gas is passed through an aqueous solution of ferric chloride acidified with dilute H2SO4, no change is observed. Flowever when, zinc dust is added to the solution, ferric chloride (FeCl3) is reduced to ferrous chloride (FeCI2) and the solution turns colourless.

Earlier, it was considered that nascent hydrogen (which is more reactive in nature) produced due to the reaction between zinc dust and dilute sulphuric acid was responsible for the reduction of ferric chloride to ferrous chloride.

However, it has been proved that the reduction is due to the electrons released by the metals in the acid solution. Nascent hydrogen has no role in reducing the compounds, rather the metal acts as the reductant.

Zn atoms release electrons and get converted to Zn2+ ions. Fe3+ ions accept those electrons and are reduced to Fe2+ ions. Again H+ ions present in the solution are also reduced to hydrogen gas simultaneously by accepting the electrons released by zinc atoms.

⇒ \(\mathrm{Zn} \rightarrow \mathrm{Zn}^{2+}+2 e \text { (oxidation) }\)

⇒ \(2 \mathrm{Fe}^{3+}+2 e \rightarrow 2 \mathrm{Fe}^{2+} \text { (reduction) }\)

⇒ \(\mathrm{H}^{+}+e \rightarrow \mathrm{H} \text { (reduction); } \mathrm{H}+\mathrm{H} \rightarrow \mathrm{H}_2 \uparrow\)

It should also be noted that, nowadays the concept of nascent oxygen is also considered to be obsolete.

Question 50. Write with equation what happens when zinc dust is added to hot and concentrated caustic soda solution.

Answer:

Zinc dust reacts with hot and concentrated caustic soda solution (NaOH) to produce sodium zincate (Na2ZnO2) salt and hydrogen gas.

⇒ \(\mathrm{Zn}+2 \mathrm{NaOH} \rightarrow \mathrm{Na}_2 \mathrm{ZnO}_2+\mathrm{H}_2 \uparrow\)

Question 51. Concentrated sodium hydroxide (NaOH) solution should not be boiled in aluminium vessels. Why?

Answer:

Aluminium reacts with sodium hydroxide solution (NaOH) to form soluble sodium aluminate salt along with the evolution of hydrogen gas. As a result, the vessels get corroded.

⇒ \(2 \mathrm{Al}+2 \mathrm{NaOH}+2 \mathrm{H}_2 \mathrm{O} \rightarrow 2 \mathrm{NaAlO}_2+3 \mathrm{H}_2 \uparrow\)

So, concentrated NaOH solution should not be boiled in aluminium vessels.

Question 52. Mention some uses of sodium hydroxide in industries.

Answer:

Sodium hydroxide is a widely used chemical in different industries. Some of its uses are as follows

  1. Sodium hydroxide is used in the manufacture of soaps, paper and synthetic fibres.
  2. It is used in the production of organic dyes.
  3. It is used in the refining of petroleum-based products.
  4. Caustic soda (NaOH) is used as a reagent in the industrial preparation of different chemicals.

Question 53. Concentrated acids are diluted by adding the acid into water and not by adding water into the acid. Why?

Answer:

Large amount of heat is evolved when water is added to acid and this causes the acid to boil. As a result, the acid may spurt out from the beaker and cause serious accident.

Apart from this, the glass beaker may break due to evolution of excess amount of heat. So, the acid is gradually added to large amount of water with continuous stirring.

Question 54. Why should one be cautious while working with concentrated acids or Concentrated alkalis?

Answer:

Concentrated acids or concentrated alkalis are highly corrosive substances. They cause blister-like wounds on human skin. Burns caused due to acids and alkalis are known as acid burns and alkali burns respectively.

Concentrated acids are extremely harmful for eyes. Apart from these, acids may cause burning sensation, blackening of skin and also damage the living tissues.

Acid vapours if inhaled may cause breathing troubles. Concentrated alkalis also produce similar problems. Thus, one should, be careful while working with concentrated acids or concentrated alkalis.

Question 55. What do you mean by acid burns and alkali bums?

Answer:

When concentrated mineral acids like HCI, H2SO4, HNO3 etc., and concentrated alkalis like NaOH, KOH etc., come in contact with our skin, these cause blisters on our skin and even burn it.

The burns caused by the corrosive action of acids are known as acid burns while the burns caused by the corrosive action of strong alkalis ate known as alkali burns.

WBBSE Solutions For Class 9 Physical Science Chapter 4 Topic A Concept Of Acid And Bases Acid Burns And Alkali Burns

Question 56. What are the steps that should be immediately taken in case of an acid burn or an alkali burn?

Answer:

Concentrated acids or alkalis cause blisters on our skin. In such cases, the affected part should be immediately washed with plenty of water repeatedly.

In case of an acid burn, the affected part should be treated with 1% dilute sodium bicarbonate solution and in case of an alkali burn, the affected part should be washed with 1% acetic acid solution. After the preliminary treatment is done, one should consult a doctor.

Question 57. Human skin becomes yellowish when it mcomes in contact with dilute nitric acid. Why?

Answer:

Dilute nitric acid reacts with proteins present in the human skin to form yellow-coloured xanthoproteic acid. This makes the skin yellowish.

Question 58. Human skin blackens when it is exposed to concentrated sulphuric acid. Why?

Answer:

Concentrated sulphuric acid is strongly hygroscopic and corrosive in nature. When it comes in contact with human skin, it absorbs water from the skin causing the skin to blacken.

Question 59. What changes will be observed in the colour of a litmus paper when it comes in contact with dry HCI gas and an aqueous solution of hydrogen chloride gas?

Answer:

No change will be observed in the colour oflitmus paper when it comes in contact with dry HCI gas. However, the litmus paper turns red in aqueous solution of hydrogen chloride gas.

Question 60. HCI gas is not an acid, but aqueous solution of HCI is strongly acidic. Why?

Answer:

Hydrogen chloride is a covalent compound. It does not dissociate in gaseous state or in liquid state to produce H+ ion. Hence, hydrogen chloride gas is not an acid but is a neutral compound.

However, in aqueous solution, polar water molecules separate the partially positively charged H-atom from partially negatively charged Cl-atom in the polar H — Cl molecule.

Consequently, HCI molecules ionise to form H+ and Cl ions. H+ ions further combines with water molecules to form H3O+ ions and thus, aqueous solution of HCI shows acidic property.

WBBSE Solutions For Class 9 Physical Science Chapter 4 Topic A Concept Of Acid And Bases Sodium Biocarbonate And Tartaric Acid

For example, if a dry mixture of sodium bicarbonate and tartaric acid is taken in a glass and the mouth of the glass is covered with a deflated balloon, no change is observed.

However, if some water is added to the glass and the deflated balloon is placed at the mouth of the flask, it is seen that the balloon gets inflated due to the liberation of CO2 gas.

Question 61. A mixture of tartaric acid crystals and sodium bicarbonate undergo chemical reaction only in presence of water. Explain with reason.

Answer:

Tartaric acid and sodium bicarbonate do not react with each other in dry state because they do not behave as acids or bases in dry state. However, when water is added to the mixture, tartaric acid ionises to produce H+ ions which in turn react with bicarbonate ions (HCO3) produced due to dissociation of sodium bicarbonate to liberate CO2 gas.

⇒ \(\mathrm{H}^{+}+\mathrm{HCO}_3^{-} \rightarrow \mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2 \uparrow\)

Question 62. HCI is added to silver nitrate solution.

Answer:

When silver nitrate (AgNO3) solution is added to hydrochloric acid, insoluble silver chloride (AgCI) is produced which forms a curdy white precipitate.

⇒ \(\mathrm{AgNO}_3+\mathrm{HCl} \underset{\text { (curdy white) }}{\rightarrow \mathrm{AgCl} \downarrow}+\mathrm{HNO}_3\)

Question 63. Dilute hydrochloric acid is added to calcium carbonate.

Answer:

Calcium carbonate or marble reacts with dilute hydrochloric acid to produce calcium chloride (CaCI2) and carbon dioxide gas.

\(\mathrm{CaCO}_3+2 \mathrm{HCl} \rightarrow \mathrm{CaCl}_2+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2 \uparrow\)

Question 64. A mixture of concentrated HCI and Mno2 is heated.

Answer:

When a mixture of manganese dioxide (MnO2) and concentrated HCI is heated, HCI reduces MnO2 to manganous chloride (MnCl2) and itself gets oxidised to evolve greenish-yellow chlorine gas.

⇒ \(\mathrm{MnO}_2+4 \mathrm{HCl} \rightarrow \mathrm{MnCl}_2+\mathrm{Cl}_2 \uparrow+2 \mathrm{H}_2 \mathrm{O}\)

Question 65. Ammonia is allowed to react with hydrogen chloride gas.

Answer:

Ammonia gas reacts with hydrogen chloride (HCI) gas to produce dense white fumes of ammonium chloride (NH4CI).

⇒ \(\mathrm{NH}_3(g)+\mathrm{HCl}(g) \rightarrow \mathrm{NH}_4 \mathrm{Cl}(s)\)

Question 66. Dilute hydrochloric acid (HCI) is kept in an aluminium vessel.

Answer:

If dilute HCI is kept in an aluminium vessel, then aluminium reacts with the dilute acid to produce aluminium chloride (AlCI3) along with evolution of hydrogen gas. Thus, the vessel gets corroded.

⇒ \(2 \mathrm{Al}+6 \mathrm{HCl} \rightarrow 2 \mathrm{AlCl}_3+3 \mathrm{H}_2 \uparrow\)

Question 67. Aqueous sodium carbonate is treated with hydrogen chloride (HCI) gas.

Answer:

Aqueous sodium carbonate reacts with hydrogen chloride (HCI) gas to produce sodium chloride, carbon dioxide and water.

⇒ \(\mathrm{Na}_2 \mathrm{CO}_3+2 \mathrm{HCl} \rightarrow 2 \mathrm{NaCl}+\mathrm{CO}_2 \uparrow+\mathrm{H}_2 \mathrm{O}\)

Question 68. Metallic copper Is treated with concentrated HCI in presence of oxygen.

Answer:

Metallic copper slowly reacts with hot and concentrated HCI in presence of oxygen to produce cupric chloride (CuCI2) and water.

⇒ \(2 \mathrm{Cu}(s)+\mathrm{O}_2(g)+4 \mathrm{HCl}(a q) \rightarrow \stackrel{\Delta}{2 \mathrm{CuCl}_2(a q)+2 \mathrm{H}_2 \mathrm{O}(I)}\)

Question 69. Concentrated HNO3 is added dropwiseon hot charcoal.

Answer:

When concentrated nitric acid is added dropwise to hot charcoal (carbon), carbon gets oxidised to carbon dioxide (CO2) gas while nitric acid gets reduced to form reddish-brown nitrogen dioxide (NO2) gas.

⇒ \(\mathrm{C}+4 \mathrm{HNO}_3 \rightarrow \mathrm{CO}_2 \uparrow+4 \mathrm{NO}_2 \uparrow+2 \mathrm{H}_2 \mathrm{O}\)

Question 70. Copper is heated with concentrated nitric acid.

Answer:

When copper is heated with concentrated nitric acid, copper is oxidised by nitric acid to form cupric nitrate. [Cu(NO3)2]. Nitric acid itself gets reduced to nitrogen dioxide.

⇒ \(\mathrm{Cu}+4 \mathrm{HNO}_3 \rightarrow \mathrm{Cu}\left(\mathrm{NO}_3\right)_2+2 \mathrm{NO}_2 \uparrow+2 \mathrm{H}_2 \mathrm{O}\)

Question 71. Hot and concentrated nitric acid is kept in an iron vessel.

Answer:

Hot and concentrated nitric acid initially reacts with iron to produce ferric nitrate [Fe(NO3)3], NO2 and water.

⇒ \(\mathrm{Fe}+6 \mathrm{HNO}_3 \rightarrow \mathrm{Fe}\left(\mathrm{NO}_3\right)_3+3 \mathrm{NO}_2 \uparrow+3 \mathrm{H}_2 \mathrm{O}\)

Ferric nitrate then decomposes to form ferric oxide which forms a layer over the iron vessel and prevents further reaction of iron with the acid.

⇒ \(4 \mathrm{Fe}\left(\mathrm{NO}_3\right)_3 \rightarrow 2 \mathrm{Fe}_2 \mathrm{O}_3+12 \mathrm{NO}_2+3 \mathrm{O}_2 \uparrow\)

Question 72. Metallic magnesium is treated with very dilute nitric add.

Answer:

Metallic magnesium reacts with very dilute nitric acid to form magnesium nitrate [Mg(NO3)2] and hydrogen gas.

⇒ \(\mathrm{Mg}+2 \mathrm{HNO}_3 \rightarrow \mathrm{Mg}\left(\mathrm{NO}_3\right)_2+\mathrm{H}_2 \uparrow\)

Question 73. Cold and dilute nitric acid is added to copper.

Answer:

Copper reacts with cold and dilute nitric acid to form cupric nitrate [Cu(NO3)2], nitrous oxide (N2O) and water.

⇒ \(4 \mathrm{Cu}+10 \mathrm{HNO}_3 \rightarrow 4 \mathrm{Cu}\left(\mathrm{NO}_3\right)_2+\mathrm{N}_2 \mathrm{O} \uparrow+5 \mathrm{H}_2 \mathrm{O}\)

Question 74. Hot and concentrated nitric acid is added dropwise on red-hot pumice stone.

Answer:

When hot and concentrated nitric acid is added dropwise on red-hot pumice stone, the acid decomposes to form nitrogen dioxide (NO2) gas along with oxygen and water vapour.

⇒ \(4 \mathrm{HNO}_3 \rightarrow 4 \mathrm{NO}_2 \uparrow+2 \mathrm{H}_2 \mathrm{O} \uparrow+\mathrm{O}_2 \uparrow\)

Question 75. Nitric acid vapour is passed over metallic copper.

Answer:

Metallic copper reacts with nitric acid vapour to produce cupric oxide (CuO) and water along with evolution of nitrogen gas.

⇒ \(5 \mathrm{Cu}+2 \mathrm{HNO}_3 \rightarrow 5 \mathrm{CuO}+\mathrm{N}_2 \uparrow+\mathrm{H}_2 \mathrm{O}\)

Question 76. Copper is treated with 1:1 HNO3 at room temperature.

Answer:

Blue-coloured cupric nitrate, nitric oxide gas and water are formed by the reaction of cccper 1 : 1 HNO3 at room temperature.

⇒ \(3 \mathrm{CU}+8 \mathrm{HNO}_3 \rightarrow 3 \mathrm{Cu}\left(\mathrm{NO}_3\right)_2+4 \mathrm{H}_2 \mathrm{O}+2 \mathrm{NO} \uparrow\)

Question 77. A mixture of potassium nitrate and concentrated H2SO4 is heated around 200ºC.

Answer:

When a mixture of potassium nitrate and concentrated H2SO4 is heated around 200ºC, potassium hydrogen sulphate KHSO4 and nitric acid are produced.

⇒ \(\mathrm{KNO}_3+\mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{KHSO}_4+\mathrm{HNO}_3\)

Question 78. Dilute sulphuric acid is added to barium chloride solution.

Answer:

When dilute sulphuric acid is aaced to barium chloride (BaCI2) solution, white barium su pnate is precipitated which is insoluble in hytrochiorc acid (HCI) and nitric acid (HNO3).

⇒ \(\mathrm{H}_2 \mathrm{SO}_4+\mathrm{BaCl}_2 \underset{\text { (white) }} \rightarrow \mathrm{BaSO}_4 \downarrow+2 \mathrm{HCl}\)

Question 79. Concentrated H2SO4 is heated with copper turnings.

Answer:

When concentrated H2SO4 is heated with copper turnings, copper sulphate is produced and ‘ sulphur dioxide gas having a smell of burnt S sulphur is liberated.

⇒ \(\mathrm{Cu}(s)+2 \mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{CuSO}_4(a q)+\mathrm{SO}_2 \uparrow+2 \mathrm{H}_2 \mathrm{O}(I)\)

Question 80. Concentrated sulphuric acid H2SO4 is added to formic acid.

Answer:

When concentrated H2SO4 is added to formic acid, sulphuric acid absorbs water molecules from formic acid and produces carbon monoxide (CO).

⇒ \(\mathrm{HCOOH}+\mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{CO} \uparrow+\left[\mathrm{H}_2 \mathrm{O}+\mathrm{H}_2 \mathrm{SO}_4\right]\)

Chapter 4 Matter Acids Bases And Salts Topic A Concept Of Acid And Bases Very Short Answer Type Questions Choose The Answer

Question 1. A covalent compound whose aqueous solution is acidic is

  1. CH4
  2. CCI4
  3. HCI
  4. NH

Answer: 3. HCI

Question 2. A covalent compound whose aqueous solution is alkaline

  1. CH4
  2. CCI4
  3. HCI
  4. NH

Answer: 4. NH

Question 3. One of the limitations of Arrhenius acid-base theory is that

  1. It is applicable only for organic solvents
  2. It is applicable only for inorganic solvents
  3. Water is essentially required as the solvent
  4. No solvent is required

Answer: 3. Water is essentially required as the solvent

Question 4. In aqueous solution H+ ion is present as

  1. Hion
  2. H2+ ion
  3. H3O+ ion
  4. H3O ion

Answer: 3. H3O+ ion

Question 5. Which of the following is used to prepare soaps and detergents?

  1. HNO3
  2. HCI
  3. H2SO4
  4. NaOH

Answer: 4. NaOH

Question 6. Which of the following is known as ‘aqua fortis’?

  1. NaOH
  2. HNO3
  3. HCI
  4. H2SO4  

Answer: 2. HNO3

Question 7. Which of the following is called the ‘king of chemicals’?

  1. NaOH
  2. HNO3
  3. HCI
  4. H2SO4  

Answer: 4. H2SO4  

Question 8. The acid used in the preparation of starch from glucose is

  1. HCI
  2. HNO3
  3. H2SO4  
  4. H3PO4  

Answer: 1. HCI

Question 9. Aqua regia is a

  1. 3:1 mixture of concentrated HCI and concentrated HNO3
  2. 1:3 mixture of concentrated HCI and concentrated H2SO4
  3. 2:3 mixture of HNO3 and H2SO4
  4. 1:1:1 mixture of HCI, HNO3 and H2SO4

Answer: 1. 3:1 mixture of concentrated HCI and concentrated HNO3

Question 10. Which of the following does not produce hydrogen on reacting with dilute acids?

  1. Fe
  2. Zn
  3. Cu
  4. Mg

Answer: 3. Cu

Question 11. Which of the following can produce hydrogen by reacting with cold and very dilute HNO3?

  1. Fe
  2. Zn
  3. Cu
  4. Mg

Answer: 4. Mg

Question 12. The compound used to identify H2SO4 is

  1. BaSO4
  2. BaCI2
  3. Ba(OH)2
  4. BaCO3

Answer: 2. BaCI2

Question 13. Which of the following is identified by using an aqueous solution of AgNO3?

  1. HCI
  2. HNO3
  3. H2SO4
  4. NaOH

Answer: 1. HCI

Question 14. NaOH reacts with HCI in

  1. Dry condition
  2. Aqueous solution
  3. Benzene solution
  4. CCL solution

Answer: 2. Aqueous solution

Question 15. Which of the following is not a mineral acid?

  1. Hydrochloric acid
  2. Citric acid
  3. Sulphuric acid
  4. Nitric acid

Answer: 2. Citric acid

Question 16. Which of the following is not a base?

  1. NaOH
  2. KOH
  3. NH4OH
  4. C2H5OH

Answer: 4.C2H5OH

Question 17. Which of the following is a strong hygroscopic substance?

  1. Cone. H2SO4
  2. Cone. HNO3
  3. Cone. HCI
  4. CH3COOH

Answer: 1. Cone. H2SO4

Question 18. Which of the following can be identified through ring test?

  1. HCI
  2. H2SO4
  3. NaOH
  4. HNO3

Answer: 4. HNO3

Question 19. \(\mathrm{Zn} \underset{\mathrm{HNO}_3}{\stackrel{\text { dil, cold }}{\longrightarrow}} \mathrm{Zn}\left(\mathrm{NO}_3\right)_2+X+\mathrm{H}_2 \mathrm{O}\); Here ‘X’ is

  1. N2O
  2. NO
  3. NO2
  4. NH4NO3

Answer: 4. NH4NO3

Question 20. The brown ring compound formed in the ring test is

  1. \(\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_5(\mathrm{NO})_2\right] \mathrm{SO}_4\)
  2. \(\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_5 \mathrm{NO}\right] \mathrm{SO}_4\)
  3. \(\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_5 \mathrm{NO}\right]\left(\mathrm{SO}_4\right)_2\)
  4. \(\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_5 \mathrm{NO}\right] \mathrm{SO}_4\)

Answer: 2. \(\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_5 \mathrm{NO}\right] \mathrm{SO}_4\)

Question 21. Brown fumes is seen to be coming out of the surface of which acid?

  1. HNO3
  2. H2CO3
  3. H2SO4
  4. HCI

Answer: 1. HNO3

Question 22. The gas formed by heating Cu-turnings with I cone. HN03 is

  1. CO2
  2. NO2
  3. NO
  4. N2O

Answer: 2. NO2

Question 23. According to Arrhenius Theory, an acid produces (in aqueous medium)

  1. H ion as only anion
  2. H ion as only cation
  3. OH ion as only anion
  4. OH ion as only cation

Answer: 2. H ion as only cation

Question 24. The metal which produces H2 in reaction with acid as well as with base is

  1. Copper
  2. Magnesium
  3. Zinc
  4. Iron

Answer: 3. Zinc

Question 25. If acid falls on any body part, which one of the following should be used to wash it off?

  1. Sodium bicarbonate solution
  2. Lemon juice
  3. Lime water
  4. Caustic soda solution

Answer: 1. Sodium bicarbonate solution

Question 26. Which one of the following is formed by the reaction of copper with cold and dil. HNO3?

  1. NO
  2. NO2
  3. N2O
  4. N2

Answer: 3. N2O

Question 27. Which one of the following is hydracid?

  1. H2SO4
  2. HNO3
  3. HCI
  4. HCOOH

Answer: 3. HCI

Question 28. The acid which is secreted inside the stomach is

  1. HNO3
  2. H2SO4
  3. HCI
  4. H2CO3

Answer: 3. HCI

Question 29. Cone. H2SO4 is a

  1. Deliquescent substance
  2. Efflorescent substance
  3. Crystalline substance
  4. Hygroscopic substance

Answer: 4. Hygroscopic substance

Question 30. The gas produced by the reaction of MnO2 with dil. hydrochloric acid is

  1. H2
  2. O2
  3. CI2
  4. N2

Answer: 3. CI2

Chapter 4 Matter Acids Bases And Salts Topic A Concept Of Acid And Bases Answer In Brief

Question 1. For which property of water, an acid ionises in water to produce H3O+ ions?

Answer: Due to the polar nature of water, an acid ionises in water to produce H3O+ ions.

Question 2. Give some examples of organic acid.

Answer: Acetic acid (CH3COOH), formic acid (HCOOH) etc., are some examples of organic acid.

Question 3. Name an inorganic acid which is synthesised in human body.

Answer: Hydrochloric acid (HCl).

Question 4. Show the reaction for dissociation of HNO3 and CH3COOH in aqueous medium.

Answer:

⇒ \(\mathrm{HNO}_3+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{H}_3 \mathrm{O}^{\oplus}+\mathrm{NO}_3^{\ominus}\)

⇒ \(\mathrm{CH}_3 \mathrm{COOH}+\mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{CH}_3 \mathrm{COOH}^{\ominus}+\mathrm{H}_3 \mathrm{O}^{\oplus}\)

Question 5. Give an example (name and formula) of a weak acid.

Answer: Acetic acid (CH3COOH).

Question 6. Name two acids used in daily life.

Answer: Examples of acids used in daily life are

  1. Acetic acid (vinegar is used in cooking),
  2. Hydrochloric acid (muriatic acid is used to clean bathrooms).

Question 7. Name a base which is not a metallic oxide or hydroxide.

Answer: Ammonia (NH3).

Question 8. Name two basic substances used in daily life.

Answer: Washing soda (Na2CO3) and baking soda (NaHCO3) are two basic substances used in daily life.

Question 9. Can BCI3 be considered as an acid according to Arrhenius theory?

Answer: BCI3 cannot be considered as an acid as it does notyield any H+ ion in aqueous solution.

Question 10. Name a metal which cannot produce hydrogen gas by reacting with dilute mineral acids.

Answer: Copper.

Question 11. Give example of a volatile mineral acid.

Answer: Hydrochloric Acid (HCI).

Question 12. Name a covalent gaseous compound which ionises in water and acts as a strong acid.

Answer: Hydrogen chloride (HCI) is a gaseous covalent compound which ionises in water and acts as a strong acid.

Question 13. What is muriatic acid?

Answer: Muriatic acid is hydrochloric acid (HCI).

Question 14. Which metals can displace hydrogen from cold and dilute nitric acid?

Answer: Metals such as magnesium (Mg) and manganese (Mn) can displace hydrogen from cold and dilute nitric acid.

Question 15. Which acid is used to remove impurities from gold?

Answer: Nitric acid (HNO3).

Question 16. State the major use of aqua regia.

Answer: Aqua regia is used to dissolve noble metals like gold, silver, platinum etc.

Question 17. Which acid is used in the preparation of TNT?

Answer: Nitric acid (HNO3).

Question 18. Which gas is excreted from jewellery shops?

Answer: Nitrogen dioxide (NO2).

Question 19. Which acid is used more in jewellery industry?

Answer: HNO3 (nitric acid).

Question 20. Which acid is used to prepare nitroglycerine?

Answer: Nitric acid is used to prepare nitroglycerine.

Question 21. Which acid is used in the ring test for identification of nitric acid?

Answer: Sulphuric acid.

Question 22. Write down the name and formula of the compound which forms the brown ring in the ring test for identification of nitric acid.

Answer: Pentaaquanitrosyliron (II) sulphate and its formula is [Fe(H2O)5(NO)]SO4.

Question 23. Which acid is used in the preparation of inorganic fertiliser, ammonium sulphate?

Answer: Sulphuric acid (H2SO4).

Question 24. Name the acid which is used in the preparation of HCI(g).

Answer: Sulphuric acid (H2SO4).

Question 25. Give example of a hygroscopic acid.

Answer: Cone. H2SO4

Question 26. Which salt is produced when aluminium reacts with hot and concentrated aqueous solution of NaOH?

Answer: Sodium aluminate (NaAIO2).

Question 27. What is oil of vitriol?

Answer: Sulfuric acid is termed as oil of vitriol.

Chapter 4 Matter Acids Bases And Salts Topic A Concept Of Acid And Bases Fill In The Blanks

Question 1. The formula of hydronium ion is ________

Answer: H3O+

Question 2. A base is a compound which dissociates in water to produce _______ ions.

Answer: OH  

Question 3. Ammonia is a base because it reacts with acids to produce _______

Answer: Salts

Question 4. Fuming nitric acid is a strong ______ agent.

Answer: Oxidising

Question 5. ______ is used in the preparation of picric acid.

Answer: HNO3

Question 6. ________ is used to absorb water vapour.

Answer: H2SO4

Question 7. The base used to prepare synthetic fibre or rayon is _______

Answer: NaOH

Question 8. Copper reacts with hydrochloric acid in presence of _______

Answer: O2

Question 9. The metal which is not used in the preparation of hydrogen is ________

Answer: Cu

Question 10. Freshly prepared solution of _________ is required for the ring test.

Answer: FeSO4

Question  11. The water pollutant which is produced when Cu reacts with hot and cone. HNO3 is ______

Answer: Cu(NO3)2

Question 12. The gas which is produced when Cu reacts with hot and cone. H2SO4 is _______

Answer: SO2

Question 13. A concentrated acid is diluted by gradually adding_______ into _______

Answer: Acid, water

Question 14. A mixture of tartaric acid and sodium bicarbonate undergoes chemical reaction when ________ is added to it.

Answer: Water

Question 15. Hydrochloric acid (HCI) ionises in ________ solution and exhibits its acidic property.

Answer: Aqueous

Question 16. Hydrochloric acid (HCI) is identified by using ______ solution.

Answer: Silver nitrate

Question 17. Hydrochloric acid (HCI) reacts with Zn to produce hydrogen and ________

Answer: ZnCI2

Question 18. The basicity of an acid is the number of replaceable __________ atoms present in one molecule of the acid.

Answer: Hydrogen

Question 19. An example of a tribasic acid is _________

Answer: H3PO4

Question 20. ________ solution is used to treat alkali burns.

Answer: 1% acetic acid

Question 21. Excess secretion of acid causes _________ in stomach.

Answer: Ulcer

Question 22. If oxygen atom is present in acid, the acid is termed as ________ acid.

Answer: Oxy

Question 23. Aluminium hydroxide reacts with NaOH to produce _______ and ________

Answer: Sodium aluminate, water

Chapter 4 Matter Acids Bases And Salts Topic A Concept Of Acid And Bases State Whether True Or False

Question 1. Water soluble metal hydroxides are called alkalis.

Answer: True

Question 2. The compound responsible for the formation of brown ring in the ring test is pentaaquanitrosyliron(ll) sulphate.

Answer: True

Question 3. Prolonged secretion of acid in the stomach causes ulcer.

Answer: True

Question 4. Hydrochloric acid exhibits reducing property while nitric acid exhibits oxidising property.

Answer: True

Question 5. The basicity of H2SO4 is 1.

Answer: False

Question 6. Nitric acid is extensively used in the manufacture of explosives.

Answer: True

Question 7. HCI is the organic acid produced in human body.

Answer: False

Question 8. BaCI2 solution is used to identify HNO3.

Answer: False

Chapter 4 Matter Acids Bases And Salts Topic B Qualitative Concept Of pH Synopsis

  1. The H+ ion concentration of a dilute solution is expressed in terms of pH.
  2. pH is the negative logarithm of H+ ion concentration of a solution. pH of a neutral solution is 7 at 25°C. Any acidic solution has pH less than 7 and alkaline solution has pH greater than 7.
  3. pH-paper is used as a universal indicator to get an idea about the pH value of a solution. The paper shows different colours in solutions of different pH values.
  4. The decay of tooth enamel occurs when the pH level of mouth cavity falls below 5.5.
  5. The pH level of soil or water bodies is increased by addition of quick lime.

Chapter 4 Matter Acids Bases And Salts Topic B Qualitative Concept Of pH Short And Long Answer Type Questions

Question 1. What is meant by pH of a solution?

Answer:

pH of a solution is defined as the negative logarithm (to the base 10) of the molar concentration of H3O+ ions in the solution. pH comes from the German word Potenz de Hydrogen where Potenz means power.

⇒ \(p H=-\log _{10}\left[\mathrm{H}_3 \mathrm{O}^{+}\right]=\log _{10} \frac{1}{\left[\mathrm{H}_3 \mathrm{O}^{+}\right]}\)

where [H3O+ ] = molar concentration of H3O+ ions in the solution.

Question 2. What idea is obtained about the nature of a solution from its pH value?

Answer:

At 25°C, if the pH of a solution is less than 7, then the solution is acidic in nature. If the pH is greater than 7, then the solution is alkaline in nature whereas if the pH is equal to 7, then the solution is a neutral solution.

Question 3. What Is a pH scale? Mention the range of a pH scale.

Answer:

The scale used to express the acidic or alkaline nature of a solution with respect to the pH of the solution is called a pH-scale.

In general, the H3O+ ion concentration or OH   ion concentration of a dilute solution does not exceed 1mol • L-1.

If the H3O+ ion concentration of a solution is 1 mol • L-1 then its pH will be = \(-\log _{10}\left[\mathrm{H}_3 \mathrm{O}^{+}\right] =-\log _{10^1} 1=0\)

On the other hand, if the OH ion concentration of a solution is 1 mol • L 1, then its H3O+ ion concentration will be 10-14mol • L-1 (at 25°C \(\left[\mathrm{H}_3 \mathrm{O}^{+}\right] \times\left[\mathrm{OH}^{-}\right]=10^{-14}\)).

Hence its pH will be = \(-\log _{10}\left[\mathrm{H}_3 \mathrm{O}^{+}\right]=-\log _{10} 10^{-14}=14\)

Thus, pH of a dilute aqueous solution at 25°C ranges from 0 to 14.

WBBSE Solutions For Class 9 Physical Science Chapter 4 Topic B Qualitative Concept Of pH

Question 4. The H3O+ ion concentration in a solution at 25°C is 10-4  mol • L-1. Find the pOH of the solution.

Answer:

The H3O+ ion concentration in the solution, [H3O+] = 10-4 mol • L-1

∴ pH of the solution = \(-\log _{10}\left[\mathrm{H}_3 \mathrm{O}^{+}\right]\) = \(-\log \left(10^{-4}\right)=-(-4)=4\)

At 25°C, pH + pOH = 14

∴ pOH of the solution = 14 – pH = 14 – 4 = 10

Question 5. If the H3O+ ion concentration in a solution is 1 x 10-9 mol• L-1, then find the pH of the solution.

Answer:

The H3O+ ion concentration in the solution, [H3O+ ] = 1 x 10-9 mol • L-1

∴ pH of the solution = \(-\log _{10}\left[\mathrm{H}_3 \mathrm{O}^{+}\right]\) = \(-\log \left(1 \times 10^{-9}\right)=-(-9)=9\)

Question 6. The H3O+ ion concentration of four solutions M, N, O and P are 10-2, 10-3, 10-4 and 10-5 • mol • L-1 respectively. Find the pH of the solutions and arrange the solutions in order of their increasing acid strength.

Answer:

The H3O+ ion concentration of four solutions

M, N, O and P are 10-2, 10-3, 10-4 and 10-5 mol • L-1 respectively.

∴ \(pH of solution M =-\log _{10}\left[\mathrm{H}_3 \mathrm{O}^{+}\right]\)

= \(-\log _{10}\left(10^{-2}\right)=-(-2)=2\)

∴ \(pH of solution N =-\log _{10}\left[\mathrm{H}_3 \mathrm{O}^{+}\right]\)

= \(-\log _{10}\left(10^{-3}\right)=-(-3)=3\)

∴ \(\mathrm{pH} of solution O =-\log _{10}\left[\mathrm{H}_3 \mathrm{O}^{+}\right]\)

= \(-\log _{10}\left(10^{-4}\right)=-(-4)=4\)

∴ \(pH of solution P =-\log _{10}\left[\mathrm{H}_3 \mathrm{O}^{+}\right]\)

= \(-\log _{10}\left(10^{-5}\right)=-(-5)=5\)

We know that the acidity of a solution increases as the pH of the solution decreases. Thus, increasing order of acid strength of the solutions is P < O < N < M.

Question 7. The pH of a solution increases by 1 unit. What will be the change in H3O+ ion concentration of the solution?

Answer:

Let us consider that the pH of the given solution is 4. Therefore, the H3O+ ion concentration of the solution will be [H3O+] = 10-pH = 10-5 mol • L-1.

Now, the pH of the solution is increased by 1 unit. So, the pH of the solution now becomes 5.

Hence, the H3O+ ion concentration of the solution will be [H3O+] = 10-pH = 10-5 mol • L-1.

Thus, concentration of a dilute aqueous solution becomes l/10th of its initial concentration when pH is increased by 1 unit.

Similarly, the concentration of a dilute aqueous solution becomes 10 times of its initial concentration if the pH is decreased by 1 unit.

Question 8. State whether the pH of a solution can be less than zero or greater than 14. Justify your answer.

Answer:

At 25°C, the pH of a dilute aqueous solution generally ranges from 0 to 14 because the concentration of H3O+ or OH  ions in dilute aqueous solution usually does not exceed 1 mol • L-1.

However, if the concentration of H3O+ ions in a solution exceeds 1 g-ion L-1, then the pH of the solution becomes less than zero. Similarly, if the concentration of OH ions in a solution exceeds 1 g-ion L-1, then the pH of the solution becomes greater than 14.

Question 9. pH of the solutions P, Q and R are 13, 6 and 2 respectively.

  1. which one of these solutions will form NH3 from (NH4)2SO4?
  2. which one is strongly acidic?
  3. which solution will contain both molecules and ions?

Answer:

  1. Solution P will form NH3 from (NH4)2SO4 as it is strongly basic in nature.
  2. Solution R is strongly acidic as depicted by the given pH value.
  3. Solution Q of pH 6 will contain both molecules and ions.

Question 10. What is pH+-paper? How is it used to determine the pH of a solution?

Answer:

  1. A pH-paper is a paper coated with universal indicator which is used to get an idea about the pH of a solution.
  2. To determine the pH of a solution, the pH-paper is dipped into the solution. The paper attains a definite colour depending on the pH of the solution. The colour of the pH-paper is then compared with the standard pH colour strip and consequently, the pH of the solution is determined.

WBBSE Solutions For Class 9 Physical Science Chapter 4 Topic B Qualitative Concept Of pH pH Paper Is Determining pH Solution

Question 11. Mentionb with reason whether the pH of the aqueous solutions of vinger and soda will be grater or less than 7.

Answer:

We know, pH of acidic and basic solution are less and greater than 7 respectively.

Now the main component of vinegar is acetic acid (CH3COOH) which dissociates partially in the aqueous solution forming H3O and CH3COOΘ ion.

\(\mathrm{CH}_3 \mathrm{COOH} \rightleftharpoons \mathrm{H}^{\oplus}+\mathrm{CH}_3 \mathrm{COO}^{\ominus}\)

 

Hence the aqueous solution of vinegar will have pH less than 7.

On the other hand the aqueous solution of soda (Na2CO3) becomes alkaline due to hydrolysis.

\(\mathrm{Na}_2 \mathrm{CO}_3+2 \mathrm{H}_2 \mathrm{O} \rightarrow 2 \mathrm{NaOH}+\mathrm{H}_2 \mathrm{CO}_3\)

 

Hence the aqueous solution of soda will have pH greater than 7.

Question 12. Why does dental erosion take palce?

Answer:

The enamel of our tooth is made of calcium phosphate. During consumption of food, mainly sweets, the food particles get stuck between our teeth. These food particles are decomposed by bacteria present in our mouth to produce acids which decrease the pH level of the mouth cavity.

WBBSE Solutions For Class 9 Physical Science Chapter 4 Topic B Qualitative Concept Of pH DEntal Erosion Take Place

If the pH level falls below 5.5, then the acids react with calcium phosphate and cause erosion of the tooth enamel.

Question 13. Explain why brushing of teeth is essential after having meals?

Answer:

Food particles, especially the carbohydrate particles get stuck to the dental gap and form acids by the bacterial decomposition. As a consequence, pH inside the mouth decreases.

Dental enamel made of calcium phosphate, starts decaying at a pH less than or equal to 5.5. Most of the toothpastes have a pH around 9.0 which neutralise the formed acid at the dental gap and prevents enamel decay. That is why brushing of teeth after meal is essential.

Question 14. Sometimes lime is added to the water bodies during piscicultyure. Why?

Answer:

If the acidity of a water body increases, it affects the flora and fauna of the water body. The plants and fishes of the water body die due to excess acid. So, alkaline substances like quick lime or calcium oxide is added to water.

WBBSE Solutions For Class 9 Physical Science Chapter 4 Topic B Qualitative Concept Of pH Lime Is Added To The Water Bodies During Pisciculture

It neutralises the excess acids and maintains the acid-base balance of the water body. However, it should also be noted that excess use of lime may increase the alkali level of the water body which also adversely affects its ecosystem.

Question 15. Why is lime added to agricultural lands?

Answer:

Due to acid rain and excessive use of inorganic fertilisers like ammonium sulphate, the acidity of soil increases. As a result, the fertility of soil decreases and it becomes unfit for the growth of crops.

To revive the fertility of soil, alkaline substances like lime is added to the soil. Lime neutralises the excess acid present in the soil and makes the soil fertile.

Chapter 4 Matter Acids Bases And Salts Topic B Qualitative Concept Of pH Very Short Abswer Type Questions Choose The Correct Answers

Question 1. The hardest part of our body is

  1. Enamel of teeth
  2. Bones
  3. Skin
  4. Nails

Answer: 1. Enamel of teeth

Question 2. The pH of two solutions, A and B are 3 and 6 respectively. It means that

  1. Solution A is twice as acidic as solution B
  2. Solution B is twice as acidic as solution A
  3. Solution A is 1000 times more acidic than solution B
  4. Solution B is 1000 times more acidic than solution A

Answer: 3. Solution A is 1000 times more acidic than solution B

Question 3. The chemical nature of commonly used toothpastes is

  1. Acidic
  2. Neutral
  3. Alkaline
  4. Amphoteric

Answer: 3. Alkaline

Question 4. For which of the following solutions, pH will be maximum?

  1. 1 mol • L-1 HCI solution
  2. 0.1 mol • L-1 HCI solution
  3. 0.01 mol • L-1 HCI solution
  4. 0.001 mol • L-1 HCI solution

Answer: 4. 0.001 mol • L-1 HCI solution

Question 5. pH of lemon juice is

  1. > 7
  2. = 7
  3. < 7
  4. > 14

Answer: 3. < 7

Question 6. pH of blood is

  1. 4
  2. 5
  3. 7
  4. 7.35
  5. 7.45

Answer: 4. 7.45

Question 7. pH of milk is

  1. 5.5-5.6
  2. 3.4-3.7
  3. 6.5-6.7
  4. 8.5-9.5

Answer: 3. 6.5-6.7

Question 8. pH of a solution is expressed as

  1. -log[H3O+]
  2. -log[OH]
  3. -log[H ]
  4. log [OH]

Answer: 1. -log[H3O+]

Question 9. If the H+ ion concentration of a solution is 10-5 g-ion/litre, then the pH of the solution will be

  1. 10
  2. 5
  3. 3
  4. 7

Answer: 2. 5

Question 10. The pH at which the enamel of teeth begins to decay is

  1. 3.5
  2. 4.5
  3. 5.5
  4. 6.5

Answer: 3. 5.5

Question 11. Due to acid rain, the pH of agricultural lands

  1. Increases
  2. Decreases
  3. Remains unchanged
  4. Increases in some places and decreases in other places

Answer: 2. Decreases

Question 12. The range of the pH scale at 25°C is

  1. 0-10
  2. 0-14
  3. 0-12
  4. 1-14

Answer: 2. 0-14

Question 13. If acid is added to pure water, pH of the medium will

  1. Increase
  2. Decrease
  3. Remain same
  4. Be zero

Answer: 2. Decrease

Question 14. If a litmus paper is dipped in an alkaline solution, its colour will be

  1. Blue
  2. Red
  3. Yellow
  4. Green

Answer: 1. Blue

Question 15. Which of the solutions has the highest pH ?

  1. Caustic soda
  2. Milk of magnesia
  3. Vinegar
  4. Formic acid

Answer: 1. Caustic soda

Question 16. If a solution turns reddish-pink on addition of phenolphthalein, its pH may be

  1. 4
  2. 7
  3. 10
  4. 5

Answer: 3. 10

Question 17. Concept of pH scale was given by

  1. Arrhenius
  2. Sorensen
  3. Rutherford
  4. Lewis

Answer: 2. Sorensen

Question 18. pH of an alkaline solution may be

  1. 5.4
  2. 6.2
  3. 7
  4. 9.2

Answer: 4. 9.2

Question 19. Which is the correct order of pH?

  1. Tomato juice < water < toothpaste
  2. Water < toothpaste < tomato juice
  3. Water < tomato juice < toothpaste
  4. Toothpaste < tomato juice < water

Answer: 1. Tomato juice < water < toothpaste

Question 20. pH of pure water at 25°C is

  1. 5.7
  2. 6.2
  3. 7
  4. 7.5

Answer: 3. 7

Question 21. pH of an acidic solution may be

  1. 9.7
  2. 7
  3. 14
  4. 5.1

Answer: 4. 5.1

Question 22. pH will be lowest for

  1. NaHCO3 solution
  2. HCI solution
  3. KOH solution
  4. Na2CO3 solution

Answer: 2. HCI solution

Question 23. pH of pure water is 7. Which of the following is true for water?

  1. \(\mathrm{H}^{\oplus}+\mathrm{OH}^{\ominus} \rightleftharpoons \mathrm{H}_2 \mathrm{O}\)
  2. \(\mathrm{H}_2 \mathrm{O}+\mathrm{H}^{\oplus} \rightleftharpoons \mathrm{H}_3 \mathrm{O}^{\oplus}\)
  3. \(\mathrm{H}_2 \mathrm{O}+\mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{H}_3 \mathrm{O}^{\oplus}+\mathrm{OH}^{\ominus}\)
  4. \(2 \mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{H}_4 \mathrm{O}_2\)

Answer: 3. \(\mathrm{H}_2 \mathrm{O}+\mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{H}_3 \mathrm{O}^{\oplus}+\mathrm{OH}^{\ominus}\)

Question 24. Favourable pH of water for piscicullture should be

  1. 5.5-6.5
  2. > 8
  3. 7.5
  4. 7

Answer: 1. 5.5-6.5

Question 25. Which of the solution has the highest pH?

  1. 1 mol • L-1 HCI
  2. 0.1 mol • L-1 HCI
  3. 0.01 mol • L-1 HCI
  4. 0.001 mol • L-1 HCI

Answer: 4. 0.00lmol • L-1 HCI

Question 26. A solution turns yellow with addition of methyl orange. pH of the solution is

  1. 7
  2. 4
  3. > 7
  4. < 7

Answer: 3. > 7

Question 27. pH of vinegar is

  1. 4
  2. 5
  3. 7
  4. 7.35-7.45

Answer: 1. 4

Question 28. To reduce the acidity of soil which one of the following should be added?

  1. Bleaching powder
  2. Blue vitriol
  3. Lime
  4. Compost fertiliser

Answer: 3. Lime

Chapter 4 Matter Acids Bases And Salts Topic B Qualitative Concept Of pH Answer In Brief

Question 1. What is the concentration of H ion in pure water at 25°C?

Answer: 10 mo1. L

Question 2. In which solvent between water and benzene, an acid does not undergo ionisation?

Answer: An acid does not undergo ionisation in benzene because it is a non-polar solvent.

Question 3. What is the nature of an aqueous solution having pH = 4?

Answer: Acidic in nature.

Question 4. What is the nature of an aqueous solution having pH = 7?

Answer: Neutral in nature.

Question 5. What is the nature of an aqueous solution having pH = 9?

Answer: Alkaline in nature.

Question 6. What is the value of pH of pure water at 25°C?

Answer: The pH of pure water at 25°C is 7.

Question 7. What is the pH of rain water?

Answer: The pH of rain water is generally 5.6.

Question 8. Odd one out: litmus paper, pH paper, methyl orange, phenolphthalein.

Answer: pH paper.

Question 9. What is the major component of tooth enamel?

Answer: Calcium phosphate [Ca3(PO4)2].

Question 10. Why does acid form at the base of the tooth?

Answer: The residual food particles, especially the sugar particles get stuck to the space between the teeth and are dissociated by bacteria to form acid. Hence the statement.

Question 11. Which substance should be used to make alkaline agricultural land suitable for farming?

Answer: Compost fertilizer is generally used

Chapter 4 Matter Acids Bases And Salts Topic B Qualitative Concept Of pH Fill In The Blanks

Question 1. Scientist _______ introduced the pH scale.

Answer: Sorensen

Question 2. The term pH originates from the German word ________

Answer: Potenz de Hydrogen

Question 3. At 25°C, the maximum pH value of a dilute solution is _______

Answer: 14

Question 4. pH is the negative logarithm of _______ ion concentration in a solution.

Answer: H3O+

Question 5. Blood is slightly ______ in nature.

Answer: Alkaline

Chapter 4 Matter Acids Bases And Salts Topic B Qualitative Concept Of pH State Whether True Or False

Question 1. The pH of an aqueous solution is 3. The solution is alkaline in nature.

Answer: False

Question 2. If the H3O+ ion concentration of an aqueous solution is 1 x 10-5 mol • L-1, then the pH of the solution will be 5.

Answer: True

Question 3. Saliva is acidic in nature.

Answer: True

Question 4. pH of pure water is 7 at any temperature.

Answer: True

Chapter 4 Matter Acids Bases And Salts Topic C Acidic Basic Amphoteric Oxides And Acid Rain Synopsis

  1. Metallic oxides and hydroxides that react with acids to form salt and water are called bases. Water  soluble metallic hydroxides are called . alkalis. Ail metallic oxides and hydroxides are not water soluble. Hence, they are bases but are not termed as alkalis.  Thus, we can say that all alkalis are bases but all bases are not alkalis.
  2. The mixture consisting of 3 volumes of concentrated HCI and 1 volume of concentrated HNO3 is commonly known as aqua regia. It is exclusively used to dissolve noble metals like gold, silver, platinum etc.
  3. Oxides which react with bases to produce salt and water are known as acidic oxides. All non-metallic oxides are generally considered as acidic oxides.
  4. Oxides which react with acids to produce salt and water are known as basic oxides. In general, all metallic oxides are basic oxides.
  5. An amphoteric oxide reacts with both acids and bases to produce salt and water.
  6. When the acid level of rain water exceeds a certain value, it is called acid rain. Acid rain increases the acidity of soil and thus, decreases its fertility. It also adversely affects changing the aquatic plants and animals by increasing the acid level of water bodies.
  7. Due to acid rain, surfaces of buildings, sculptures and monuments made of marbles get covered with layers of CaSO4 making them appear lustreless. With time, the layers come off and produce scars and pits on the marble buildings. These scars are known as stone cancer.

Chapter 4 Matter Acids Bases And Salts Topic C Acidic Basic Amphoteric Oxides And Acid Rain Short And Long Answer Type Questions

Question 1. Chromium trioxide is an acidic oxide though it is a metallic oxide. Explain.

Answer:

Chromium trioxide (CrO3) dissolves in water to produce chromic acid (H2CrO4). Hence, it is an acidic oxide.

\(\mathrm{CrO}_3+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{H}_2 \mathrm{CrO}_4\)

Question 2. What are acidic oxides and give examples.

Answer:

The oxides which react with bases to form salt and water are known as acidic oxides. Generally oxides of non-metals are acidic oxides. Some examples of acidic oxides are carbon dioxide (CO2), sulphur dioxide (SO2), phosphorus pentoxide (P2O5) etc.

⇒ \(\mathrm{S}+\mathrm{O}_2 \rightarrow \mathrm{SO}_2 ; \mathrm{SO}_2+2 \mathrm{NaOH} \rightarrow \mathrm{Na}_2 \mathrm{SO}_3+\mathrm{H}_2 \mathrm{O}\)

Question 3. Define basic oxides with examples.

Answer:

The oxides which react with acids to form salt and water are known as basic oxides. Generally oxides of metals are basic oxides. Some examples re calcium oxide (CaO), ferrous oxide (FeO), magnesium oxide (MgO) etc.

\(2 \mathrm{Ca}+\mathrm{O}_2 \rightarrow 2 \mathrm{CaO} ; \mathrm{CaO}+2 \mathrm{HCl} \rightarrow \mathrm{CaCl}_2+\mathrm{H}_2 \mathrm{O}\)

Question 4. Define amphoteric oxides with examples.

Answer:

The oxides which react with both acids and bases to form salt and water are called amphoteric oxides. Some examples are, zinc oxide (ZnO), aluminium oxide (Al2O3) etc.

⇒ \(\mathrm{ZnO}+2 \mathrm{HCl} \rightarrow \mathrm{ZnCl}_2+\mathrm{H}_2 \mathrm{O}\)

⇒ \(\mathrm{ZnO}+2 \mathrm{NaOH} \rightarrow \mathrm{Na}_2 \mathrm{ZnO}_2+\mathrm{H}_2 \mathrm{O}\)

Question 5. why is aluminium oxide called an amphoteric oxide?

Answer:

Aluminium oxide reacts with both acids and bases separately to form salt and water.

WBBSE Solutions For Class 9 Physical Science Chapter 4 Topic C Aluminium Oxide Called And Amphoteric Oxide

So, aluminium oxide is known as an amphoteric oxide.

Question 6. Classify the following oxides: \(\mathrm{ZnO}, \mathrm{SO}_2 \text {, }\mathrm{P}_2 \mathrm{O}_5, \mathrm{~K}_2 \mathrm{O}, \mathrm{Al}_2 \mathrm{O}_3\).

Answer:

Acidic oxides: \(\mathrm{SO}_2, \mathrm{P}_2 \mathrm{O}_5\)

Basic oxides: \(\mathrm{Na}_2 \mathrm{O}, \mathrm{K}_2 \mathrm{O}\)

Amphoteric oxides: \(\mathrm{ZnO}, \mathrm{Al}_2 \mathrm{O}_3\)

Question 7. What are acid anhydrides?

Answer:

The oxide of a non-metal (acidic oxide) which dissolves in water to form its corresponding acid is called an acid anhydride. For example, phosphorus pentoxide (P2O5) dissolves in water to form phosphoric acid (H3PO4). Thus, phosphorus pentoxide is the anhydride of phosphoric acid.

⇒ \(\mathrm{P}_2 \mathrm{O}_5+3 \mathrm{H}_2 \mathrm{O} \rightarrow 2 \mathrm{H}_3 \mathrm{PO}_4\)

Question 8. Define mixed acid anhydride with example.

Answer:

If a non-metallic oxide dissolves in water to produce more than one acid, then the oxide is considered as the anhydride of both the acids and is called a mixed acid anhydride.

For example, NO2 dissolves in cold water to produce nitrous acid (HNO2) and nitric acid (HNO3). Hence, NO2 is a mixed acid anhydride.

⇒ \(2 \mathrm{NO}_2+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{HNO}_2+\mathrm{HNO}_3\)

Question 9. How is HNO3, formed by lightning?

Answer:

N2 and O2 of the atmosphere reacts with each other during lightning to form nitric oxide.

⇒ \(\mathrm{N}_2+\mathrm{O}_2 \stackrel{\text { lightning }}{\longrightarrow} 2 \mathrm{NO}\)

This nitric oxide then combines with oxygen to form nitrogen dioxide. Nitrogen dioxide then reacts with rain water to form nitric acid.

⇒ \(2 \mathrm{NO}+\mathrm{O}_2 \rightarrow 2 \mathrm{NO}_2\)

⇒ \(3 \mathrm{NO}_2+\mathrm{H}_2 \mathrm{O} \rightarrow 2 \mathrm{HNO}_3+\mathrm{NO}\)

Question 10. What is acid rain?

Answer:

Normal rainwater is slightly acidic. However, if rain water contains excess amount of acids like H2SO4 , HNO3 and HCI, then the pH of rain water ranges between 3.5-5.6. This is known as acid rain.

Question 11. What are the causes of acid rain?

Answer:

Different causes of acid rain can be classified into two categories—natural and man-made causes. Acidic oxides emitted due to natural causes and different human activities mix with the atmospheric water vapour to cause acid rain.

1. Natural Causes:

  1. SO2 gas is released into the atmosphere during volcanic eruptions
  2. Nitrogen and oxygen present in air combine to form different oxides of nitrogen NOx during lightning discharges.
  3. Bacterial decomposition of ammonium salts present in soil also produces oxides of nitrogen (NOx) that are released into the atmosphere.

2. Man-Made Causes:

  1. Different oxides of sulphur and nitrogen are released into the atmosphere due to combustion of fossil fuels like coal and petroleum used in automobiles, thermal power plants, oil refineries, metal extraction industries etc.
  2. Huge amounts of HCI gas is released from factories where hydrochloric acid is extensively used.
  3. These gases react with atmospheric oxygen, ozone and water vapour to produce different acids which float in air in the form of aerosols and come down on the earth’s surface along with rain water.

Question 12. What is stone cancer?

Answer:

Stone Cancer:

Scars and pits formed on the surface of buildings, sculptures, memorials and monuments made of marble due to acid rain are collectively called stone cancer. The scars are formed due to the reaction of the acid with marble (calcium carbonate, CaCO3).

Question 13. Discuss the harmful effects of acid rain.

Answer:

Harmful Effects Caused By Acid Rain

The harmful effects of acid rain are as follows

WBBSE Solutions For Class 9 Physical Science Chapter 4 Topic C Acidic Basic Amphoteric Oxides And Acid Rain Harmful Effects Of Acid Rain

1. Effect On Soil And Vegetation:

Acid rain increases acidity of soil. The increased acidity changes the solubilities of different metal salts in the soil. Consequently, fertility of the soil decreases which reduces the agricultural productivity. Photosynthetic activities of the plants get disrupted due to acid rain. Soil microorganisms and other living organisms of the soil are also adversely affected due to acid rain.

2. Effect On Aquatic Plants And Animals:

Acid rain decreases normal pH of different water bodies which in turn decreases reproductive capacity of fish leading to decresed production of spawns. Excessive increase in the acid level of water kills the flora and fauna of the water body and disturbs the marine ecosystem.

3. Effect On Human Beings:

Due to acid rain, some metals dissolve in rain water to form toxic salts which on entering the human body cause harmful effects. Acid rain damages our skin, hair and body cells. Acids like H2SO4 and HNO3 present in acid rain enter the human body and adversely affect our nervous system, respiratory system and digestion process.

4. Effect on sculptures and monuments: Acid rain causes extensive damage to buildings, memorials, monuments and sculptures made of marble. Marble (CaCO3) reacts with acids and forms insoluble calcium sulphate that deposits on the surfaces of the buildings. This causes scars, pits on the surface and erodes it.

⇒ \(\mathrm{CaCO}_3+\mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{CaSO}_4 \downarrow+\mathrm{CO}_2 \uparrow+\mathrm{H}_2 \mathrm{O}\)

Chapter 4 Matter Acids Bases And Salts Topic C Acidic Basic Amphoteric Oxides And Acid Rain Vert Short Answer Type Questions Choose The Correct Answer

Question 1. An example of an acidic oxide is

  1. CaO
  2. Na2O2
  3. CO2
  4. MgO

Answer: 3. CO2

Question 2. An example of a basic oxide is

  1. CO2
  2. No
  3. CaO
  4. SO

Answer: 3. CaO

Question 3. An example of an amphoteric oxide is

  1. ZnO
  2. CaO
  3. MgO
  4. FeO

Answer: 1. ZnO

Question 4. Acid rain has adversely affected

  1. Taj Mahal
  2. Victoria Memorial
  3. Sculptures made of marbles
  4. All of these

Answer: 4. All of these

Question 5. As a consequence of acid rain, pH of soil

  1. Increases
  2. Decreases
  3. Remains unaltered
  4. Sometime increases, sometime decreases

Answer: 2. Decreases

Question 6. Which of the following can form each of acidic, basic and amphoteric oxide?

  1. S
  2. Pb
  3. Ca
  4. Cr

Answer: 4. Cr

Question 7. The gas released from Mathura oil refinery which is the reason behind the weathering of the Taj Mahal is

  1. CO2
  2. CH4
  3. CO
  4. SO2

Answer: 4. SO2

Question 8. Number of amphoteric oxides among Cr2O3, ZnO, PbO, Al2O3 is

  1. 1
  2. 2
  3. 3
  4. 4

Answer: 4. 4

Question 9. The gas responsible for acid rain is

  1. CH4
  2. NO2
  3. N2O
  4. O3

Answer: 2. NO2

Question 10. Which of the following elements form acidic oxide?

  1. Na
  2. Mg
  3. P
  4. AI

Answer: 3. P

Question 11. N2O5 is

  1. Acidic oxide
  2. Basic oxide
  3. Amphoteric oxide
  4. Neutral oxide

Answer: 1. Acidic oxide

Question 12. Which one is not an acid anhydride?

  1. CO2
  2. CO
  3. N2O5
  4. SO3

Answer: 2. CO

Question 13. Which one of water, carbon dioxide, calcium oxide and nitrogen dioxide is a neutral oxide?

  1. Water
  2. Carbon dioxide
  3. Calcium oxide
  4. Nitrogen dioxide

Answer: 1. Water

Question 14. Depict the number of acidic oxides among \(\mathrm{SO}_2, \mathrm{~N}_2 \mathrm{O}_5, \mathrm{NO}_2, \mathrm{SO}_3, \mathrm{O}_3, \mathrm{CO}_2, \mathrm{H}_2 \mathrm{O},\mathrm{CO}, \mathrm{BaO}_2 and \mathrm{P}_2 \mathrm{O}_5\)?

  1. 6
  2. 8
  3. 4
  4. 7

Answer: 1. 6

Question 15. Which one of the following is a bicompound of oxygen, but not an oxide?

  1. OF2
  2. NO2
  3. SO2
  4. CO2

Answer: 1. OF2

Question 16. Which one of the following is an acidic oxide?

  1. MnO
  2. Mn2O3
  3. MnO2
  4. Mn2O7

Answer: 4. Mn2O7

Chapter 4 Matter Acids Bases And Salts Topic C Acidic Basic Amphoteric Oxides And Acid Rain Answer In Brief

Question 1. Name some metallic oxides which exhibit acidic property in water.

Answer: Manganese heptoxide (Mn2O7), chromium trioxide (CrO3) etc.

Question 2. Give some examples of acidic oxide.

Answer: Some examples of acidic oxide are carbon dioxide (CO2), sulphur trioxide (SO3) etc.

Question 3. Name two acidic metallic oxide.

Answer: Manganese heptoxide (Mn2O7) and chromium trioxide (CrO3).

Question 4. Which type of oxide is P2O5?

Answer: P2O5 is an acidic oxide.

Question 5. Which class of oxides does calcium oxide belong to?

Answer: Calcium oxide belongs to the class of basic oxide.

Question 6. Give some examples of amphoteric oxide.

Answer: Some examples of amphoteric oxide are zinc oxide (ZnO), aluminium oxide (Al2O3) etc.

Question 7. Which acid is formed when carbon dioxide (CO2) gas dissolves in water?

Answer: Carbonic acid (H2CO3).

Question 8. Which acid is formed when nitrogen dioxide (NO2) gas dissolves in water?

Answer: Nitric acid (HNO3) and nitrous acid (HNO2)

Question 9. Which acid is formed when sulphur dioxide (SO2) gas dissolves in water?

Answer: Sulphurous acid (H2SO3).

Question 10. Which gas dissolves in water to produce sulphuric acid?

Answer: Sulphur trioxide (SO3).

Question 11. Give an example of neutral oxide.

Answer: Water (H2O).

Question 12. Give example of a base which is neither metallic oxide nor metallic hydroxide.

Answer: Ammonia (NH3).

Question 13. What is the pH range of acid rain?

Answer: pH range of acid rain is 3.5 to 5.6;

Question 14. Write down the names of two gases responsible for acid rain.

Answer: SO2 and NO2 gas.

Chapter 4 Matter Acids Bases And Salts Topic C Acidic Basic Amphoteric Oxides And Acid Rain Fill In the Blanks

Question 1. The corrosion of marble buildings and monuments caused by acid rain is known as ______

Answer: Stone cancer

Question 2. An amphoteric oxide reacts with both ______ and _______ to produce salts and water.

Answer: Acids, bases

Question 3. ________ oxides are generally acidic in nature.

Answer: Non-metallic

Question 4. ________ oxides are generally basic in nature.

Answer: Metallic

Question 5. An acid present in acid rain is _______

Answer: H2SO4 or HNO3

Question 6. SO2 dissolves in water to produce ______ acid.

Answer: Sulphurous

Question 7. The product formed due to oxidation of SO2 dissolves in water to produce ________ acid.

Answer: Sulphuric

Question 8. ________ is an example of mixed acid is an anhydride.

Answer: NO

Question 9. Aluminium oxide is an example of ________ oxide.

Answer: Amphoteric

Question 10. Fe3O4 is an example of _______ oxide.

Answer: Mixed

Question 11. Example of neutral oxide is ________

Answer: H2O

Chapter 4 Matter Acids Bases And Salts Topic C Acidic Basic Amphoteric Oxides And Acid Rain State Whether True Or False

Question 1. Nitrogen dioxide dissolves in water to form nitric acid only.

Answer: False

Question 2. Acid rain mainly consists of the acids like HCI, H2SO4 and CH3COOH .

Answer: False

Question 3. CO is an acidic oxide.

Answer: False

Question 4. Example of an amphoteric oxide is Al2O3.

Answer: True

Question 5. PbO is an amphoteric oxide.

Answer: True

Question 6. CO is dissolved in acid rain.

Answer: False

Question 7. NO is an acidic oxide.

Answer: False

Chapter 4 Matter Acids Bases And Salts Topic D Neutralisation Indicator Antacids Salts And Their Classification Synopsis

  1. The substances which indicate the end point of an acid-base neutralisation reaction by changing their colour are known as acid-base indicators.
  2. Equivalent amount of an acid reacts quantitatively with equivalent amount of a base to neutralise each other and produce salt and water. This reaction is known as neutralisation reaction.
  3. Antacids are chemical compounds which are basic in nature and neutralise excess hydrochloric acid secreted in the stomach.
  4. The salt formed when all the replaceble hydrogen atoms of an acid are completely replaced by a metal or some other basic radical is known as a normal salt.
  5. The salt formed when the replaceable hydrogen atoms of a dibasic or polybasic acid are partially replaced by a metal or some other basic radical is known as an acid salt.
  6. The salt formed when the hydroxyl group (OH) of a base or an alkali is partially replaced by an acid radical is known as a basic salt.

Chapter 4 Matter Acids Bases And Salts Topic D Neutralisation Indicator Antacids Salts And Their Classification Short And Long Answer Type Questions

Question 1. What are add-base indicators? Name two acid-base indicators.

Answer:

The chemical substances which indicate the end point of an acid-base neutralisation reaction by changingtheir colour are called acid-base indicators.

Two widely used acid-base indicators are methyl orange and phenolphthalein.

Question 2. What changes will be observed in the colour of a litmus paper when it comes in contact with dry ammonia gas and aqueous solution of ammonia?

Answer:

No change will be observed in the colour of litmus paper when it comes in contact with dry ammonia gas. However, the litmus paper turns blue in aqueous solution of ammonia.

Question 3. What is acid-base neutralisation reaction?

Answer:

Equivalent amount of an acid reacts quantitatively with equivalent amount of a base to produce salt and water and as a result, both the acid and the base lose their individual properties.

This reaction is known as acid-base neutralisation reaction. For example, 1 gram-equivalent HCI reacts with 1 gram-equivalent NaOH to produce salt and water. Both HCI and NaOH lose their individual properties in course of this reaction.

⇒ \(\begin{gathered}
\mathrm{HCl}(a q) \rightarrow \mathrm{H}^{+}(a q)+\mathrm{Cl}^{-}(a q) \\
\mathrm{NaOH}\left((a q) \rightarrow \mathrm{Na}^{+}(a q)+\mathrm{OH}^{-}(a q)\right) \\
\hline \mathrm{HCl}(a q)+\mathrm{NaOH}(a q) \rightarrow \mathrm{NaCl}(a q)+\mathrm{H}_2 \mathrm{O}(l)
\end{gathered}\)

Question 4. What is neutralisation point? How is neutralisation point determined?

Answer:

In an acid-base reaction, the point at which the acid and the base quantitatively react with each other to produce salt and water and as a result, the solution becomes neutral is known as neutralisation point.

The neutralisation point of an acid-base reaction is identified by using an indicator. An indicator indicates the neutralisation point by changing its colour.

Question 5. How wilt you differentiate between Na2CO3 and NaHCO3 solution with one drop of an indicator?

Answer:

Both Na2CO3 and NaHCO3 hydrolyse in their aqueous solutions to form NaOH thereby making the resulting solution alkaline. However, the pH value of Na2CO3 solution is greater than that of NaHCO3.

Hence, on addition of one drop of phenolphthalein to Na2CO3 solution, the solution turns pink. On the other hand, if one drop of phenolphthalein is added to NaHCO3 solution, the solution remains colourless.

Hence one drop of phenolphthalein is sufficient to differentiate between Na2CO3 solution and NaHCO3 solution.

Question 6. Mention the characteristic features of indicators used in neutralisation reactions. Mention the criteria for choosing an indicator for neutralisation reaction with example.

Answer:

An acid-base indicator should be such that it can exhibit different colours in acidic, basic and neutral solutions. For example, methyl orange is yellow in alkaline solution, pinkish-red in acidic solution and orange in neutral solution.

An acid-base indicator is chosen for a particular neutralisation reaction on the basis of the change in pH-value of the solution at the equivalence point or end point.

The selected indicator must exhibit a sharp change in colour in the same pH range as required around the end point. For example, in the neutralisation of HCI and NaOH, a sharp change in pH of the solution from 3.34 to 9.7 is observed around the end point.

The pH range of methyl orange is 3.4-4.4. Hence, methyl orange can be used for the neutralisation reaction of HCI and NaOH.

Question 7. Tabulate the colours exhibited by the following indicators in acidic, basic and neutral medium—methyl orange, litmus, phenolphthalein and methyl red.

Answer:

The colours exhibited by the given indicators in acidic, basic and neutral medium are tabulated below

WBBSE Solutions For Class 9 Physical Science Chapter 4 Topic D Neutralisation Indicator Antacids Salts And Their Classificatio Indicator Colors

WBBSE Solutions For Class 9 Physical Science Chapter 4 Topic D Neutralisation Indicator Antacids Salts And Their Classification

Question 8. How is an indicator chosen for an acid- base neutralisation reaction?

Answer:

At the end point of an acid-base neutralisation reaction, there is a rapid and sharp change in the pH of the solution. The indicators which can change their colour in that pH-range are selected for those acid-base neutralisation reactions.

For example, in the neutralisation of a strong acid and a strong base, the range of pH change is maximum near the end point. The pH range of almost all the indicators lies in this range.

Hence, any indicator is suitable for titration of a strong acid and a strong base. On the other hand, in the neutralisation of a weak acid and a weak base, the range of pH change is minimum near the end point.

No suitable indicator having pH range in this region has been found. Hence, the titration of a weak acid and a weak base is not possible.

Question 9. Mention the colour of the solutions if phenolphthalein is added to them.

  1. NaCl
  2. Ca(OH)2
  3. HCI
  4. MgCI2.

Answer:

WBBSE Solutions For Class 9 Physical Science Chapter 4 Topic D Neutralisation Indicator Antacids Salts And Their Classification Phenolphthalein Is Added To Them

Question 10. What are antacids? Give some examples.

Answer:

The substances which are used to neutralise the excess hydrochloric acid secreted in the stomach and maintain the pH of the gastric juice at an optimum level, are known as antacids.

Gelusil, Digene, Diovol are some of the commonly used antacids.

Question 11. Write the compositions of common antacids, Gelusil and Diovol.

Answer:

Gelusil is composed of aluminium hydroxide, magnesium trisilicate and siloxane.

Diovol is composed of aluminium hydroxide, magnesium carbonate and magnesium hydroxide.

Question 12. What are systemic land non-systemic antacids? Give examples of each.

Answer:

Systemic antacids: The antacids which get readily dissolved and absorbed in blood and hence, disturb the acid-base balance of the body are called systemic antacids.

They follow a definite mechanism to reduce acidity. Common examples include sodium bicarbonate, sodium citrate etc.

Non-systemic antacids: Non-systemic antacids are insoluble and are very poorly absorbed in the blood. Hence, they do not disturb the acid-base balance of the body.

They do not follow any definite mechanism of functioning as antacids. Some common examples include aluminium hydroxide, different calcium salts etc.

WBBSE Solutions For Class 9 Physical Science Chapter 4 Topic D Sytemic ANd Non Systemic Antacids

Question 13. What is milk of magnesia? Write its uses and side effects.

Answer:

Milk of magnesia: Aqueous suspension of magnesium hydroxide is known as milk of magnesia. It contains 7-8% magnesium hydroxide.

Uses:

  1. Magnesium hydroxide is an effective antacid.  It rapidly reacts with HCI produced in stomach and neutralises the acid. Hence, it provides quick relief from acidity.
  2. It is often used along with AI(OH)3 as antacid. This provides quick relief from acidity and eliminates any possibility of constipation due to AI(OH)3.

Side Effects:

  1. HCI reacts with Mg(OH)2 to produce MgCl2 which may cause diarrhoea.
  2. Deposition of magnesium in the kidneys can cause toxic effect in the body.

Question 14. Discuss the uses and side effects of sodium bicarbonate as antacid.

Answer:

Uses: Sodium bicarbonate is highly soluble in water and hence, it works rapidly as an antacid. However, it acts for a relatively short duration.

Side Effects:

  1. Sodium bicarbonate produces CO2 in the stomach which may cause uneasiness and infection in the bile duct.
  2. It disturbs the acid-base balance of the body.
  3. It increases the Na+ ion concentration in blood which may cause high blood pressure.

Question 15. Discuss the uses and side effects of aluminium hydroxide as antacid.

Answer:

Uses: Aluminium hydroxide is used to decrease the hyperacidity of stomach. It works slowly and hence, takes time to relieve the pain. Large amount of acid is produced in the stomach due to peptic ulcer, dyspepsia etc.

These result in chest pain, uneasiness, acidity etc. Aluminium hydroxide readily reacts with the excess acid in the stomach and provides relief.

Side Effects:

  1. Excess use of AI(OH)3 may cause constipation.
  2. Prolonged and continuous use of AI(OH)3 may decrease the phosphate level of blood. As a result, the excretion of Cu through urine increases which results in renal rickets.

Question 16. State whether the aqueous solution of all normal salts are neutral in nature.

Answer:

A normal salt is produced due to complete neutralisation of an acid and a base. So, the aqueous solution of a normal salt should be neutral in nature.

However, there are a number of normal salts whose aqueous solutions are either acidic or alkaline in nature. The cations and anions produced from these salts in their aqueous solutions react with water molecules thereby increasing the concentration of H3O+ or OH  ions. As a result, the solution becomes acidic or alkaline accordingly.

Apart from a salt of strong acid and strong base, the solutions of all other normal salts are either acidic or alkaline.

For example, NH4CI is a normal salt of strong acid, HCI and weak alkali, NH4OH . The hydrolysis of this salt produces excess H3O+ ions in water and the aqueous solution becomes acidic.

On the other hand, Na2CO3 is a salt of weak acid, H2CO3 and strong base, NaOH. It hydrolyses to produce excess OH ions in the solution thus, making it alkaline in nature.

Question 17. Baking soda was used in earlier days as antacid. But nowadays Mg(OH)2, AI(OH)3 are used instead. State the reason behind it.

Answer:

Baking soda can disturb the acid-base equilibrium of the body is it can be absorbed by blood. Baking soda can also interfere with how the body absorbs some medications.

Now-a-days, Mg(OH)2 and AI(OH)3 are used instead. These antacids do not destroy the acid- base equilibrium inside the body as they do not get absorbed by blood. These antacids form corresponding salt and water to decrease the acidity by neutralising the excess amount of HCI present in stomach.

Question 18. What is meant by basicity of an acid?

Answer:

The number of replaceable hydrogen atoms present in 1 molecule of an acid or the number of H+ (or H3O+) ions furnished by 1 molecule of the acid in aqueous solution is called the basicity of the acid.

For example, 1 molecule of HCI dissociates in aqueous solution to produce one H+ ion while 1 molecule of H2SO4 dissociates to give two H+ ions. So, the basicity of HCI and H2SO4 are 1 and 2 respectively.

Question 19. What is meant by acidity of a base?

Answer:

The number of OH ions produced by 1 molecule of a base is called the acidity of the base. In other words, it may be defined as the. number of molecules of a monobasic acid required to neutralise 1 molecule of the base quantitatively.

For example, 1 molecule of NaOH furnishes one OH ion in aqueous solution and 1 molecule of monobasic acid, HCI is required for complete neutralisation of 1 molecule of NaOH. Hence, acidity of NaOH is 1.

Question 20. Define normal salt with examples.

Answer:

The salt produced when all the replaceable hydrogen atoms of an acid are completely replaced by a metal or basic radical is known as normal salt. Some examples are sodium chloride (NaCI), zinc sulphate (ZnSO4) etc.

\(\mathrm{Zn}+\mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{ZnSO}_4+\mathrm{H}_2\)

 

A molecule of H2SO4 has two replaceable hydrogen atoms. Zn reacts with sulphuric acid and replaces both the hydrogen atoms forming ZnSO4. Thus, ZnSO4 is a normal salt.

Question 21. Define acidic salts with examples.

Answer:

Acidic Salts :-

The salt produced when the replaceable hydrogen atoms of a polyprotic acid is partially replaced by a metal or basic radical is known as acidic salt. For example, sodium bisulphate (NaHS04), sodium bicarbonate (NaHCO3) etc.

⇒ \(\mathrm{H}_2 \mathrm{SO}_4+\mathrm{NaOH} \rightarrow \mathrm{NaHSO}_4+\mathrm{H}_2 \mathrm{O}\)

H2SO4 has two replaceable hydrogen atoms. NaHSO4 (sodium bisulphate) is produced when one hydrogen atom of sulphuric acid is replaced by Na-atom. Hence, NaHSO4 is an acidic salt.

Question 22. Define basic salts with examples.

Answer:

Basic Salts :-

The salt produced when the replaceable hydroxyl radicals of a base or an alkali are partially replaced by an acid radical is known as basic salt. Some examples of basic salts are basic lead nitrate [Pb(OH)NO3], basic lead chloride [Pb(OH)CI] etc.

Example 23. Explain ‘sodium bicarbonate is an acid salt’.

Answer:

Sodium Bicarbonate Is An Acid Salt :-

Sodium bicarbonate is the salt of strong alkali, NaOH and weak acid.H2CO3. Now H2CO3 is a dibasic acid (\(\mathrm{H}_2 \mathrm{CO}_3 \rightleftharpoons 2 \mathrm{H}^{\oplus}+\mathrm{CO}_3^{2-}\)) and of the two replaceable hydrogens of H2CO3, one H-atom is replaced by Na-atom to form NaHC03. That is why NaHCO3 is an acid salt.

Question 24. HCI and HNO3 always form normal salts but H2SO4 can form both normal and acid salts—Explain why.

Answer:

HCI and HNO3 are monobasic acids. By the replacement of the only replacable H-atom, corresponding normal salts can only be formed. On the other hand, H2SO4 is a dibasic acid. So there is a probability of formation of both acid salt and normal salt.

When one of the two replacable ‘H’ is replaced by metal ion, acid salt is formed and when both of the replaceable hydrogen atoms are replaced by metal atoms, normal salt is formed.

Question 25. Mention the name and formula of a normal salt and an acid salt which are used in everyday life.

Answer:

Normal Salt And An Acid Salt :-

A normal salt used in everyday life is sodium chloride (NaCI) or common salt.

An acid salt used in everyday life is baking powder or sodium bicarbonate (NaHCO3).

Question 26. Aqueous solution of sodium bicarbonate is alkaline although it Is an acid salt—Explain.

Answer:

Sodium bicarbonate dissociates into Na and HCO3Θ  of ion in aqueous solution.

⇒ \(\mathrm{NaHCO}_3 \rightleftharpoons \mathrm{Na}^{\oplus}+\mathrm{HCO}_3^{\ominus}\)

Now in aqueous solution the tendency of loosing a proton (H+) from HCO3Θ ion is less than the tendency to accept a proton. So HCO3 accepts a proton to form undissociated H2CO3.

⇒ \(\mathrm{HCO}_3^{\ominus}+\mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{H}_2 \mathrm{CO}_3+\mathrm{OH}^{\ominus}\)

So the concentration of OHΘ ion increases in the aqueous solution of NaHCO3. As a result the solution becomes alkaline.

Chapter 4 Matter Acids Bases And Salts Topic D Neutralisation Indicator Antacids Salts And Their Classification Very Short Answer Type Questions Choose The Correct Answer

Question 1. An example of an acid-base indicator is

  1. Methyl alcohol
  2. Methyl orange
  3. Methyl chloride
  4. Methylamine

Answer: 2. Methyl orange

Question 2. In neutral solution, the colour of litmus is

  1. Violet
  2. Red
  3. Orange
  4. Yellow

Answer: 1. Violet

Question 3. An indicator which shows pink colour in alkaline solution is

  1. Litmus
  2. Methyl orange
  3. Phenolphthalein
  4. Methyl red

Answer: 3. Phenolphthalein

Question 4. In neutral solution, the colour of methyl red indicator is

  1. Red
  2. Blue
  3. Yellow
  4. Orange

Answer: 4. Orange

Question 5. In acidic solution, the colour of litmus is

  1. Blue
  2. Red
  3. Yellow
  4. Violet

Answer: 2. Red

Question 6. An aqueous solution of sodium carbonate (Na2CO3) is alkaline because it is a salt consisting of

  1. Strong acid and strong base
  2. Weak acid and weak base
  3. Strong acid and weak base
  4. Weak acid and strong base

Answer: 4. Weak acid and strong base

Question 7. An acid salt is produced when sodium hydroxide (NaOH) reacts with

  1. HCI
  2. HNO3
  3. H2SO4
  4. CH3COOH

Answer: 3. H2SO4

Question 8. The indicator used in the titration of a strong acid and a weak base is

  1. Methyl orange
  2. Litmus
  3. Phenolphthalein
  4. Any indicator

Answer: 1. Methyl orange

Question 9. The indicator which is used in the titration of a weak acid and a strong base is

  1. Methyl orange
  2. Litmus
  3. Phenolphthalein
  4. Any indicator

Answer: 3. Phenolphthalein

Question 10. The indicator which is used to differentiate between aqueous solutions of Na2CO3 and NH4CI is

  1. Methyl orange
  2. Litmus
  3. Phenolphthalein
  4. Any indicator

Answer: 3. Phenolphthalein

Question 11. The indicator used in the titration of a strong acid and a strong base is

  1. Methyl orange
  2. Methyl red
  3. Phenolphthalein
  4. Any indicator

Answer: 4. Any indicator

Question 12. The indicator suitable for titration of a weak acid and a weak base is

  1. Methyl orange
  2. Phenolphthalein
  3. Any indicator
  4. No indicator is suitable

Answer: 4. No indicator is suitable

Question 13. Omeprazole is used as a/an

  1. Pain killer
  2. Antipyretic
  3. Drug to decrease acid secretion in the stomach
  4. Analgesic

Answer: 3. Drug to decrease acid secretion in the stomach

Question 14. An example of a systemic antacid is

  1. NaHCO3
  2. AI(OH)3
  3. NaOH
  4. Ca(OH)2

Answer: 1. NaHCO3

Question 15. An example of a non-systemic antacid is

  1. NaHCO3
  2. Al(OH)3
  3. NaOH
  4. Ca(OH)2

Answer: 2. Al(OH)3

Question 16. An example of a normal salt is

  1. Na2HPO4
  2. NaH2PO4
  3. NaH2PO3
  4. Na2SO4

Answer: 4. Na2SO4

Question 17. Which of the following is the major component of milk of magnesia?

  1. Fe(OH)3
  2. Mn(OH)2
  3. Mg(OH)2
  4. Ca(OH)2

Answer: 3. Mg(OH)2

Question 18. An example of an acidic salt is

  1. Na2SO4
  2. NaH2PO2
  3. NaCl
  4. Na2HPO4

Answer: 4. Na2HPO4

Question 19. An example of a basic salt is

  1. Pb(OH)CI
  2. PbCl2
  3. Pb(OH)2
  4. PbO

Answer: 1. Pb(OH)CI

Question 20. The aqueous solution of which of the following salts is acidic?

  1. NH4CI
  2. NaCl
  3. Na2SO4
  4. CH3COONa

Answer: 1. NH4CI

Question 21. The compound used as an antacid

  1. Ca(OH)2
  2. Mg(OH)2
  3. ZnO
  4. NaOH

Answer: 2. Mg(OH)2

Question 22. Which olne of the following is a tribasic acid?

  1. H3PO3
  2. H3PO4
  3. CH3COOH
  4. H3PO2

Answer: 2. H3PO4

Question 23. Baking powder is

  1. Acid
  2. Base
  3. Acid salt
  4. Salt

Answer: 3. Acid salt

Question 24. To neutralise the excess acid of stomach, which one is used

  1. Antibiotic
  2. Antacid
  3. Analgesic
  4. Antiseptic

Answer: 2. Antacid

Question 25. To form basic salt, minimum acidity of a base should be

  1. 1
  2. 2
  3. 3
  4. None of the above

Answer: 2. 2

Question 26. Number of neutral salts among NaH2PO2, Na2HPO3, Na2SO4, Ca(OH)CI is

  1. 1
  2. 2
  3. 3
  4. 4

Answer: 2. 2

Question 27. A component of digestive juices is

  1. H2SO4
  2. HNO3
  3. HCI
  4. HCOOH

Answer: 3. HCI

Question 28. The colour observed by adding a drop of phenolphthalein to an aqueous solution of washing soda is

  1. Red
  2. Blue
  3. Colourless
  4. Pink

Answer: 4. Pink

Question 29. Which of the following compounds is not used as antacid?

  1. Sodium bicarbonate
  2. Calcium carbonate
  3. Sodium hydroxide
  4. Aluminium silicate

Answer: 3. Sodium hydroxide

Question 30. Which of the following compound is present in baking powder?

  1. Na2CO3
  2. H2CO3
  3. NaHCO3
  4. CaCO3

Answer: 3. NaHCO3

Chapter 4 Matter Acids Bases And Salts Topic D Neutralisation Indicator Antacids Salts And Their Classification Answer In Brief

Question 1. Name two acid-base indicators.

Answer: Methyl orange and phenolphthalein are two widely used acid-base indicators.

Question 2. How do indicators indicate the end point of an acid-base neutralisation reaction?

Answer: An indicator indicates the end point of an acid-base neutralisation reaction by changing its colour.

Question 3. Name an indicator which exhibits orange colour in neutral solution.

Answer: Methyl orange.

Question 4. Name two indicators which exhibit yellow colour in alkaline solution.

Answer: Methyl orange and methyl red exhibit yellow colour in alkaline solution.

Question 5. Give an example of an acid which can produce two types of salts by reacting with a base.

Answer: Sulphuric acid (H2SO4) reacts with a base to produce two types of salts (acid salt and normal salt). It partially reacts with NaOH to produce an acid salt, sodium bisulphate (NaHSO4) and on complete neutralisation it produces a normal salt, sodium sulphate (Na2SO4).

Question 6. Name an indicator that can be used for the neutralisation reaction of CH3COOH and NaOH.

Answer: Phenolphthalein.

Question 7. Name an indicator that can be used for the neutralisation reaction of H2SO4 and NaOH.

Answer: Any indicator.

Question 8. Name an indicator that can be used for the neutralisation reaction of CH3COOH and NH4OH.

Answer: No indicator is suitable for the neutralisation reaction of weak acid, CH3COOH and weak base, NH4OH.

Question 9. what will be the colour of the Na2CO3 solution on addition of methyl orange?

Answer: Yellow.

Question 10. Neutralisation reaction is mainly the reaction of which ions?

Answer: H and OHΘ.

Question 11. State the number of molecules of caustic soda required to neutralise 1 molecule of sulfuric acid.

Answer: 2 molecules of caustic soda are required.

Question 12. What is the chemical name of widely used antacid, Zantac?

Answer: The chemical name of widely used antacid Zantac is ranitidine.

Question 13. How does the stomach get affected if acidity continues for a prolonged period of time?

Answer: If acidity continues for a prolonged period of time, it causes ulcer in the stomach.

Question 14. Name the acid salts produced when orthophosphoric acid reacts with NaOH.

Answer: Disodium hydrogen phosphate (Na2HPO4) and sodium < dihydrogen phosphate (NaH2PO4).

Question 15. Name an acid which always forms normal salt when it reacts with bases.

Answer: Hydrochloric acid (HCI).

Question 16. Give the name and formula of an acid salt which is formed due to partial neutralisation of a monobasic acid.

Answer: An acid salt which is formed due to partial neutralisation of a monobasic acid such as, hydrogen fluoride (HF) is potassium bifluoride (KHF2).

Question 17. What is the reason behind ‘alkalosis disease’?

Answer: Alkalosis disease Can be caused by taking excess NaHCO3 as antacid.

Question 18. Give an example of a salt without a metal atom.

Answer: Ammonium chloride (NH4CI).

Question 19. State about the nature of the aqueous solution of NaHSO4.

Answer: The aqueous solution of NaHSO4 is acidic.

Question 20. Write down the names of two main components of antacid.

Answer: Aluminium hydroxide [AI(OH)3] and magnesium hydroxide [Mg(OH)2].

Question 21. Write down the formula of the acid salt obtained from the reaction of phosphoric acid and magnesium hydroxide.

Answer: MgHPO4, (magnesium hydrogen phosphate).

Question 22. What is ‘milk of magnesia’?

Answer: Aqueous suspension of magnesium hydroxide.

Chapter 4 Matter Acids Bases And Salts Topic D Neutralisation Indicator Antacids Salts And Their Classification Fill In The blanks

Question 1. The indicator which turns colourless in acidic solution is ___________

Answer: Phenolphthalein

Question 2. The colours of methyl orange and methyl red change in _______ solution.

Answer: Acidic

Question 3. ________ indicator turns blue in alkaline medium.

Answer: Litmus

Question 4. Universal indicator is actually a _______ of some selective indicators.

Answer: Mixture

Question 5. _______ types of salts are produced when NaOH reacts with H2SO4.

Answer: Two

Question 6.  HNO3 reacts with NaOH to produce _______ type of salt.

Answer: One

Question 7. The name of the salt, CuSO• Cu(OH)2 is ________

Answer: Basic copper sulphate

Question 8. ______ and _______ are produced in an acid-base neutralisation reaction.

Answer: Salt, water

Question 9. The indicators used in acid-base titrations are generally very weak organic _______ or organic _______

Answer: Acid, bases

Question 10. _______ is an example of a systemic antacid.

Answer: Sodium bicarbonate

Question 11. _______ is an example of a non-systemic antacid.

Answer: Aluminium hydroxide

Question 12. _______ is a normal salt of an inorganic base and an organic acid.

Answer: CH3COONa

Question 13. [Cu(NH3)4]SO4 is a _______ salt.

Answer: Complex

Question 14. The colour of the KCI solution will be _________ phenolphthalein is added to it.

Answer: Colourless

Question 15. NaH2PO2 is a ________ salt.

Answer: Neutral

Question 16. The colour of methyl orange in acid solution is _________

Answer: Pink

Question 17. NaHSO4 is an example of _________ salt.

Answer: Acid

Question 18. Sodium bicarbonate is an example of _________ salt.

Answer: Acid

Question 19. Methyl orange turns _______ in neutral solution.

Answer: Orange

Question 20. Acidity of H3PO4 is ________

Answer: 3

Chapter 4 Matter Acids Bases And Salts Topic D Neutralisation Indicator Antacids Salts And Their Classification State Whether True Or False

Question 1. Methyl orange indicator turns colourless in basic solution.

Answer: False

Question 2. Phenolphthalein can be used as an indicator in the neutralisation reaction of CH3COOH and NH4OH.

Answer: False

Question 3. Sodium chloride and zinc sulphate belong to the category of normal salt.

Answer: True

Question 4. Excessive use of aluminium hydroxide as antacid for a long period of time may cause renal rickets.

Answer: True

Question 5. Excessive use of chemical fertilisers on agricultural lands for a long period of time makes the soil alkaline.

Answer: False

Question 6. Sodium carbonate is an alkali.

Answer: F

Question 7. Oxalic acid is a dibasic acid.

Answer: True

Question 8. Sodium surface is an acidic salt.

Answer: False

Chapter 4 Matter Acids Bases And Salts Topic D Neutralisation Indicator Antacids Salts And Their Classification Miscellaneous Type Questions

Match The column

1.

WBBSE Solutions For Class 9 Physical Science Chapter 4 Topic D Neutralisation Indicator Antacids Salts And Their Classification Match The Column 1

Answer: 1. C, 2. A, 3. D, 4. B

2.

WBBSE Solutions For Class 9 Physical Science Chapter 4 Topic D Neutralisation Indicator Antacids Salts And Their Classification Match The Column 2

Answer: 1. B, 2. D, 3. A, 4. C

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