WBBSE Solutions For Class 8 School Science Chapter 2 Element Compound And Chemical Reaction Nature Of Matter Long Answer Type Questions

Chapter 2 Element Compound And Chemical Reaction Nature Of Matter Long Answer Type Questions

Question 1. What do you mean by acidic oxide and basic oxide? Illustrate with a suitable example.
Answer:

Acidic oxide and Basic oxide:

Generally, the oxide compounds formed by the chemical reaction between a non-metal and oxygen are acidic oxides. The aqueous solution of them is acidic.

If a blue litmus paper is dipped in this solution, it turns red. For example, carbon is a non-metal, it forms carbon dioxide (CO2) when it reacts with oxygen. CO2 is an acidic oxide.

When C02 reacts with water, it forms carbonic acid, which is a weak acid.

⇒ \(\begin{gathered}
\mathrm{C}+\mathrm{O}_2 \rightarrow \mathrm{CO}_2 \\
\mathrm{CO}_2+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{H}_2 \mathrm{CO}_3
\end{gathered}\)

Generally, the oxide compounds formed by the chemical reaction between a metal and oxygen are basic oxides. The aqueous solution of them is basic.

If a red litmus paper is dipped in this solution, it turns blue. For example, calcium is a metal, it forms calcium oxide (CaO) when reacts with oxygen.

CaO is a basic oxide. When CaO reacts with water, it forms calcium hydroxide, which is basic.

⇒ \(\begin{gathered}
2 \mathrm{Ca}+\mathrm{O}_2 \rightarrow 2 \mathrm{CaO} \\
\mathrm{CaO}+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{Ca}(\mathrm{OH})_2
\end{gathered}\)

Question 2. Hydrated cupric nitrate, solid iodine and a magnesium filament are separately heated strongly: what will happen?
Answer:

Hydrated cupric nitrate, solid iodine and a magnesium filament are separately heated strongly:

When a magnesium filament is heated strongly, it burns to produce intense white light. After it is completely burnt, some residue is left. This is magnesium oxide.

⇒ \(2 \mathrm{Mg}+\mathrm{O}_2 \rightarrow 2 \mathrm{MgO}\)

When blue-coloured hydrated, cupric nitrate, taken in a test tube, is heated, initially some water vapour evolves which condenses at the upper part of the test tube.

Brown fumes of nitrogen dioxide evolve. After the heating is over, a black residue of cupric oxide (CuO) is left.

⇒ \(\begin{aligned}
2 \mathrm{Cu}\left(\mathrm{NO}_3\right)_2 \text { (blue) } & \rightarrow 2 \mathrm{CuO} \text { (black) } \\
+ & 4 \mathrm{NO}_2 \text { (brown fume) }+\mathrm{O}_2
\end{aligned}\)

When solid iodine is heated, no chemical reaction occurs, only solid iodine is converted to violet-coloured iodine vapour.

⇒ \(\mathrm{I}_2 \text { (solid) } \rightarrow \mathrm{I}_2 \text { (vapour) }\)

Read And Learn More WBBSE Solutions For Class 8 School Science Long Answer Type Questions

Question 3. Compare the properties of metals and non-metals.
Answer:

Comparing the properties of metals and non-metals

The characteristic properties of metals and non-metals have been compared in a tabular form as follows:

Properties of Metals Properties of Non-Metals
1 Lustrous (shining appearance) 1 Non-lustrous
2 Ductile (can be made into a thin wire) 2 Non-ductile
3 Malleable (can be hammered or pressed into different shapes easily without breaking or cracking) 3 Non-malleable
4 High melting point and boiling point (generally exists as solid at or near room temperature) 4 Low melting point and boiling point (generally exists as liquid or gas at or near room temperature)
5 High density 5 Low density
6 Good conductors of heat and electricity 6 Bad conductors of heat and electricity.

 

Question 4. Zinc powder, iron powder and some amount of ferrous sulphide are separately taken in three test tubes and to each of them some dilute sulphuric acid is added. What will happen?
Answer:

Zinc powder, iron powder and some amount of ferrous sulphide are separately taken in three test tubes and to each of them some dilute sulphuric acid is added.

The addition of dilute acids to some substances may cause chemical changes in them, forming new substances which may (or may not) have characteristic colour or odour.

So some substances may be identified by reacting them with dilute acids such as sulphuric acid or hydrochloric acid.

For example, zinc powder, iron powder and solid ferrous sulphide are taken separately in three dry test tubes. Dilute sulphuric acid (H2SO4) is added to each of them.

When dilute sulphuric acid is added to zinc powder, a colourless and odourless gas bubbles out from the mixture.

This gas burns with a blue flame when ignited with a burning stick. This gas is hydrogen (H2).

⇒ \(2 \mathrm{Mg}+\mathrm{O}_2 \stackrel{\Delta}{\longrightarrow} 2 \mathrm{MgO}\)

When dilute sulphuric acid is added to the iron powder, here also a colourless and odourless gas bubbles out from the solution.

This gas is hydrogen. The solution turns light green due to the formation of water-soluble ferrous sulphate (FeSO4).

⇒ \(\mathrm{Fe}+\mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{FeSO}_4+\mathrm{H}_2 \uparrow\)

When the same acid is added to ferrous sulphide, a gas bubbles out with the smell of a rotten egg. This gas is hydrogen sulphide (H2S). The solution turns faint green due to the formation of ferrous sulphate.

⇒ \(\mathrm{FeS}+\mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{FeSO}_4 \text { (faint green) }+\mathrm{H}_2 \mathrm{~S} \uparrow\)

Question 5. Some amount of common salt and ammonium chloride (NH4CI) is separately mixed with sodium bicarbonate or quicklime or sodium hydroxide using a mortar and a pestle. What will happen?
Answer:

Some amount of common salt and ammonium chloride (NH4CI) is separately mixed with sodium bicarbonate or quicklime or sodium hydroxide using a mortar and a pestle.

As we have just shown some substances can be identified by their reaction with dilute acids, similarly, some substances can be identified by their reaction with alkaline substances.

For example, common salt and ammonium chloride (NH4CI) are separately mixed with sodium bicarbonate (NaHCO3) or quicklime or sodium hydroxide (NaOH) using a mortar and a pestle.

In the case of common salt, no observable change occurs. But in the case of ammonium chloride, a gas evolves (vapour).

When magnesium ribbon is strongly heated, it burns brightly producing light and white-coloured magnesium oxide is formed and has a strong, pungent odour. The gas is ammonia (NH3).

When NH4CI reacts with NaHCO3:

⇒ \(\mathrm{NH}_4 \mathrm{Cl}+\mathrm{NaHCO}_3\rightarrow\mathrm{NaCl}+\mathrm{NH}_3 \uparrow+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2\) reacts with NaOH:

⇒ \(\mathrm{NH}_4 \mathrm{Cl}+\mathrm{NaOH} \rightarrow \mathrm{NaCl}+\mathrm{NH}_3 \uparrow+\mathrm{H}_2 \mathrm{O}\)

When NH4CI reacts with Ca(OH)2:

⇒ \(2 \mathrm{NH}_4 \mathrm{Cl}+\mathrm{Ca}(\mathrm{OH})_2 \rightarrow\mathrm{CaCl}_2+2 \mathrm{NH}_3 \uparrow+\mathrm{H}_2 \mathrm{O}\)

So, it is clear now that physical and chemical properties can be utilized to identify a substance.

In fact, both the physical and chemical properties of a particular substance are studied to conclusively identify the substance.

Question 6. State with a suitable example, how the reactivity of metals can be described with the help of electrochemical series.
Answer:

The reactivity of metals with respect to hydrogen can be easily explained with the help of electrochemical series. The trend of reactivity of these metals can be summarized as follows:

1. Any metal situated on the left-hand side of hydrogen is able to react with dilute acid and produce hydrogen gas.

But any metal on the right-hand side of hydrogen cannot liberate hydrogen when reacts with dilute acid.

For example, zinc is situated on the left-hand side of hydrogen in the series. So zinc granules can react with dilute sulphuric acid to produce zinc sulphate and hydrogen gas.

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

2. Any metal on the left-hand side. hydrogen can displace another metal, situated on the right-hand side of hydrogen, from its salt.

For example, in the electrochemical series iron (Fe) is situated on the left-hand side of hydrogen (H) and is expected to displace copper (Cu)from its salt(CuSO). Cu is situated at the right-hand side of hydrogen.

Experimentally also it is found that when an iron nail is dipped in an aqueous solution of copper sulphate, reddish-brown metallic copper is precipitated on the iron nails.

⇒ \(\mathrm{Fe}+\mathrm{CuSO}_4 \rightarrow \mathrm{Cu}+\mathrm{FeSO}_4\)

Properties of Metals Properties of Non-Metals
1 Lustrous (shining appearance) 1 Non-lustrous
2 Ductile (can be made into a thin wire) 2 Non-ductile
3 Malleable (can be hammered or pressed into different shapes easily without breaking or cracking) 3 Non-malleable
4 High melting point and boiling point (generally exists as solid at or near room temperature) 4 Low melting point and boiling point (generally exists as liquid or gas at or near room temperature)
5 High density 5 Low density
6 Good conductors of heat and electricity 6 Bad conductors of heat and electricity.

 

Question 7. Describe with an experiment that in general, non-metals are bad conductors of heat while metals are good conductors of heat.
Answer:

This can be easily shown by an experiment.

WBBSE Solutions For Class 8 Chapter-2 Element, compound and chemical reaction sec-1 Nature of matter charcoal powder

 

Apparatus/materials needed: two metallic containers, some iron (a metal) powder, some charcoal (a non-metal) powder, two small pieces of wax, a Bunsen burner, wire gauge.

Experiment: iron powder and charcoal powder are separately taken in two metallic containers. A piece of wax is placed on top of each container, as Then they are separately heated by a Bunsen burner. The change of state of wax is observed.

Observation: it is found that the piece of wax placed on iron powder melted quickly compared to the piece of wax placed on the top of charcoal powder.

Inference: When the metallic container is 9. heated by a Bunsen burner, the heat is conducted through the walls of the container into the iron powder.

Since the iron powder is a good conductor of heat, the heat entered into the container is quickly conducted to the piece of wax, and it melts. But, charcoal, being a non-metal is a bad conductor of heat.

So the process of conduction through it is hindered, and the wax placed on top of 11 charcoal powder is not easily melted.

Question 8. Describe in brief the importance of Ca2+ and K+ in the functioning of cardiac muscles.
Answer:

Functioning Of Heart:

Cardiac muscles require calcium to contract and squeeze blood out of the heart and into the arteries.

Calcium flows into the muscle cells and works as a switch that allows cardiac muscles to contract.

At the end of the contraction, calcium flows out of the muscle cells to allow the muscle to relax and expand again.

So the rate of heart contraction increases with increasing concentration of Ca2+ and decreases with decreasing concentration of this Ca ion.

K is also crucial to the functioning of the heart. A low level of K+ leads to irregular contraction of the heart and abnormal electrocardiogram results.

Actually, the electrocardiogram is a measure of heart function and is related to the force and rate of contraction of cardiac muscles. Too much K+ in the body may cause palpitation and disruption of heart rhythm.

Question 9. Describe in brief the importance of different ions in the contraction of muscles and conduction of nerve impulses.
Answer:

Contraction Of Muscle And Conduction Of Nerve Impulse:

Contraction and relaxation of muscles occur due to rapidly changing concentrations of Ca2+ inside the muscle cells.

This process is commonly referred to as the calcium cycle. Two proteins play a vital role in muscle contraction.

The contraction of smooth muscles is dependent on myosins and the contraction of the striated muscle depends on actin. Muscles contain myofilaments.

Contraction represents the shortening of myofilaments. Too much or too little Ca2+ causes muscular symptoms due to disruption of the calcium cycle.

Mg2+, Na+ and K+ also control the excitability of muscles. Ca2+ ion also plays a major role in the conduction of nerve impulses from one nerve cell to the other.

Question 10. Describe in brief the importance of K+ ions in maintaining the acid-base equilibrium in our body.
Answer:

The importance of K+ ions in maintaining the acid-base equilibrium in our body:

K+ ions play a significant role to maintain acid-base equilibrium in our body. Acidity (due to the high concentration of H+ ions inside the cellular fluid) causes a shift, in the concentration of K+ extracellularly.

H+ ions are then exchanged with K+ and Na+. Unless sufficient K+ and Na+ are not taken withstood, this causes alkalinity in extracellular fluid.

In the ‘same way, if the concentration of K+ and Na+ increases in extracellular fluid, then they go inside the cellular fluid and H+ ions come outside into the extracellular fluids, causing increased acidity.

Due to loss of acid-base balance, erosion of bone joints is initiated and bone density may be lowered.

Question 11. Identify the metals and non-metals present in the following compounds: NaCI, KOH, Pb(NO3)2, Ca(OH)2, MgCI2, Fe2O3, CuO, CdCl2, ZnCI2, Mn02, CoCl2, PbO; HgCl2, As2O3/ H3PO4, H2SO4.
Answer:

Compound Metal Non-metal
1 NaCI Na (sodium) Cl (chlorine)
2 KOH K (potassium) O (oxygen), H (hydrogen)
3 Pb(NO3)2 Pb (lead) N (nitrogen), O (oxygen)
4 Ca(OH)2 Ca (calcium) O (oxygen), H (hydrogen)
5 MgCI2 Mg (magnesium) Cl (chlorine)
6 Fe O Fe (iron) O (oxygen)
7 CuO Cu (copper) O (oxygen)
8 CdCI2 Cd (cadmium) Cl (chlorine)
9 ZnCI2 Zn (zinc) Cl (chlorine)
10 Mn02 Mn (manganese) O (oxygen)
11 CoCI2 Co (cobalt) Cl (chlorine)
12 PbO Pb (lead) O (oxygen)
13 HgCI2 Hg (mercury) Cl (chlorine)
14 AS2O3 NonefAs is metalloid) O (oxygen)
15 H3PO4 None H (hydrogen)
16 h2so4 None P (phosphorous), O (oxygen) H (hydrogen), S (sulphur),O (oxygen)

 

Question 12. Mention the solubility of the following substances in the four different solvents – water, kerosene, petrol, and carbon disulphide: sugar, salt, camphor, copper sulphate, and sulphur.
Answer:

Substance Solubility in
Water Kerosene Petrol Carbon disulphide
Sugar Soluble Insoluble Insoluble Insoluble
Salt Soluble Insoluble Insoluble Insoluble
Camphor Sparingly Soluble Soluble Soluble
soluble
Copper sulphate Soluble Insoluble Insoluble Insoluble
Sulphur Insoluble Insoluble Insoluble Soluble

 

Question 13. Compare different physical states of matter compared on the basis of different physical A substance can exist in three different states. properties/changes. They are solid, liquid and gas. Below, these three different physical states have been on the basis of various physical properties.
Answer:

State of matter Whether possess a definite volume Whether possess a definite shape Flow property Change of volume when pressure is increased at a constant temperature Physical Change(s) that occurs when the temperature is increased at a constant pressure If heat is extracted at constant pressure
Solid Yes Yes Nil Negligibly small change in volume In general, the volume increases, and at a certain temperature it starts melting (i.e., converted into liquid) It cools down
Liquid Yes No It has flow property (fluid) Negligibly small change in volume In general, the volume increases, and at a certain temperature, it starts boiling (i.e., converted into vapour) Gradually cools down and ultimately freezes to become solid
Gas No No It has flow property (fluid) A significant change in volume A significant change in volume occurs, but no physical change of state occurs Gradually cools down and ultimately condenses to become liquid

 

Question 14. A copper rod is placed in AgNO3 solution and FeSO4 solution. What changes do you observe? Which non-metal has been placed in the reactivity series of metals? Why is Titanium metal ideal for medical replacement structures?
Answer:

Copper is more reactive than silver. It displaces silver from silver nitrate (AgNO) solution forming copper nitrate and silver metal.

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

The solution becomes blue due to the formation of copper nitrate. A shining greyish-white deposit of silver metal is formed on the copper rod.

However copper does not react with ferrous sulphate (FeSO) solution as copper is less reactive than iron. Hydrogen (a non-metal) is placed in the reactivity series of metals.

Titanium is completely inert to human body fluids, making it ideal for medical replacement structures like hip and knee implants.

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