WBBSE Solutions For Class 9 Physical Science Chapter 4 Matter Water

Chapter 4 Matter Water Topic A Role Of Water In Development Of Life And Drinking Water Synopsis

1. Water possesses high specific heat, high boiling point, capillary action and an ability to dissolve almost all substances. Due to these unique properties of water, it helps living organisms to survive and flourish.
2. Both ionic and covalent compounds existing in solid, liquid or gaseous state can dissolve in water. Thus, water is known as the universal solvent.
3. Only 1% of the total water content of the earth constitutes of fresh water which can be used for different purposes. Rivers, streams, lakes, ponds, swamps, glaciers and groundwater are the different sources of fresh water on the earth.
4. The pH range of drinking water should be between 6.5 to 8.5 and the amount of dissolved oxygen must be 4-6 mg • L^-1 as recommended by WHO.
   Excessive presence of chlorides, fluorides and arsenic compounds in drinking water makes it unsafe for consumption.
5. The number of colonies of coliform bacteria such as E. coli present in 100 mL of a water sample is known as the coliform count of that water sample. The coliform count of drinking water must be zero.
6. Some common methods of purification of water are boiling, chlorination and use of ultraviolet rays.
7. Proportionate amount of bleaching powder is added to water in a closed vessel to make it germ-free. Then this water is left open for some time when excess chlorine evaporates from the water. The water thus obtained is safe for drinking. Sometimes, chlorine tablets are ‘ also used for the purification of water.
8. Organic substances present in water react with chlorine to form trihalomethanes (THMs) and trihaloacetic acids. (TAAs). These compounds are highly carcinogenic in nature {i.e., these cause cancer).
9. Ultraviolet rays are passed through water in aqua filters to make it germ-free. This method is better than any other water purification methods as it does not require any chemicals. Also, this method is more effective than chlorination in killing viruses present in water.

Read and Learn More WBBSE Solutions for Class 9 Physical Science and Environment

Chapter 4 Matter Water Topic A Role Of Water In Development Of Life And Drinking Water Short And Long Answer Type Questions

Question 1. What property of water makes it excellent for fomentation?

Answer:

Property Of Water Makes It Excellent For Fomentation:-

Water has the highest value of specific heat (1 cal • g^-1 • C^-1). Hence, it can absorb large amount of heat with small increase in temperature and can similarly release large amount of heat with small decrease in temperature.

So, water cools down less readily than other liquids. This is the reason for which water can be used for fomentation (i.e., to provide warmth).

Question 2. Mention one practical application of high specific heat of water.

Answer:

One Practical Application Of High Specific Heat Of Water:-

Water has a very high specific heat 4200 J • kg^-1 • K^-1 as compared to other substances (solids or liquids). Hence, the amount of heat required by a fixed quantity of water to raise its temperature by 1°C or IK is relatively higher than that required by the same quantity of some other solids or liquids.

Thus, water is used as a coolant in different industries (it helps to cool the machinery) and in radiators of automobiles.

Question 3. Land breeze and sea breeze are formed due to high specific heat of water-explain.

Answer:

Land Breeze And Sea Breeze Are Formed Due To High Specific Heat Of Water:-

Due to high specific heat of water, during daytime the landmass heats up more as compared to sea water. Consequently, air adjacent to the landmass gets heated up, becomes lighter and finally rises up to create a void space. Cold air adjacent to the sea water rushes towards the landmass to fill up the void. This is how sea breeze is resulted.

After sunset, the landmass cools down more rapidly than sea water. Air adjacent to the warm sea water heats up, becomes lighter and then rises up. Cold air adjacent to the landmass rushes towards the sea to fill up the formed void. This is how land breeze is resulted.

Question 4. What is capillary action?

Answer:

Capillary Action:-

Due to cohesive force acting between the molecules of a liquid and adhesive force operating between the liquid molecules and the surface of the vessel, a liquid elevates along a very narrow tube against the force of gravity. This phenomenon is known as capillary action.

Question 5. Discuss the significance of capillary action.

Answer:

Significance Of Capillary Action:-

1. Water and minerals absorbed by roots of plant reach the leaves by capillary action.
2. When sufficient water is not present in the upper layers of the earth’s crust, water from the lower layers come up to the upper layers by capillary action and supply water to the plants.
3. Water comes out through numerous pores on earthen pots due to capillary action. This water evaporates and consequently, cools the water within the pot.

Question 6. How do aquatic plants and animals survive in cold countries?

Answer:

Aquatic Plants And Animals Survive In Cold Countries:-

The latent heat of freezing of water is very high. In cold countries, when water at the upper layers of ponds and lakes freezes, large amount of heat is released.

The lower layers of water absorb this heat and consequently the temperature of this part of the water body increases. Thus, water at the lower levels of the water body remain at higher temperature even though the surface of the water freezes. This helps aquatic plants and animals to survive throughout the winter season in cold countries.

Question 7. Discuss the significance of dissolved oxygen for aquatic plants and animals.

Answer:

Significance Of Dissolved Oxygen For Aquatic Plants And Animals:-

Aquatic plants and animals are dependent on dissolved oxygen for carrying out their respiratory activities. A certain amount of dissolved oxygen is necessary for the aquatic organisms to survive.

Dissolved oxygen is very important for fish. If dissolved oxygen in a water body decreases, then the aquatic plants and animals will die due to lack of oxygen.

Question 8. Mention two physical properties of water which are important for evolution of life.

Answer:

Physical Properties Of Water Which Are Important For Evolution Of Life:-

Two physical properties that are very important for evolution of life are:

1. Higher specific heat of water (4200 J • Kg^-1 • K^-1)
2. Polar nature of water molecule.

Question 9. Why is water called a universal solvent?

Answer:

Water Called A Universal Solvent On Following Reasons:-

1. Water can dissolve most of the solids, liquids and gases.
2. It has very high value of dielectric constant (80.4) and so, almost all ionic compounds are soluble in water.
3. Water is a polar compound. Hence, polar covalent compounds are highly soluble in it.
4. Water exists in the liquid state over a wide range of temperature from 0°C to 100°C.

Question 10. Why is water called a polar solvent?

Answer:

Water Called A Polar Solvent Because:-

Though water molecule is formed by covalent bonds, the oxygen atom being more electronegative than hydrogen atom, becomes partially negatively charged while the hydrogen atoms become partially positively charged.

As a result, the oxygen atom of water molecule can attract the positive part of a solute molecule while hydrogen atoms of water can attract its negative part by electrostatic force of attraction. So water is called a polar solvent.

Question 11. How do electrovalent or ionic compounds easily dissolve in water?

Answer:

Ionic Compounds Easily Dissolve In Water As Follows:-

Water has a very high value of dielectric constant (80.4). Due to this, water as a solvent can separate the positively charged and negatively charged ions in an ionic compound by opposing the electrostatic force of attraction between them. Thus, molecules of these compounds easily dissociate in water yielding the constituent ions. Hence, electrovalent or ionic compounds easily dissolve in water.

Question 12. What are the drinking water?

Answer:

The Drinking Water Is:-

1. It must be colourless, odourless, tasteless and clear.
2. It must be free from floating impurities.
3. It must be free from germs and suspended particulate matter.
4. It should not contain excess minerals than permissible limit.
5. It must be free from harmful compounds such as urea, cyanide salts, nitrate salts etc.

Question 13. How do you identify a colourless liquid as water.

Answer:

We Can Identify A Colourless Liquid As Water As Follows :-

If colourless, anhydrous copper sulphate turns blue by coming in contact of a colourless liquid, then it can be told that the colourless liquid must be water.

Question 14. What will be the harmful effects if excess chloride salts are present in drinking water?

Answer:

The nature and extent of pollution caused by excess chloride salts in water largely depends on the cations of the salts. Prolonged intake of water containing excess sodium chloride may cause high blood pressure.

It must be noted that, this adverse effect is related to the presence of sodium ion in water and has no relation with the chloride ion concentration of water.

Question 15. Mention the permissible limits of the given substances in drinking water as recommended by WHO—dissolved solids, chlorides, nitrates and nitrites, fluorides, arsenic and lead.

Answer:

The permissible limits as recommended by WHO are mentioned below

1. Dissolved solids: 500 mg • L^-1
2. Chlorides: 250 mg – L^-1
3. Nitrates and nitrites: 45 mg • L^-1
4. Fluorides: 1 mg • L^-1
5. Arsenic: 0.01-0.05 mg – L^-1
6. Lead: 0.01 mg • L^-1

Question 16. How does the pH value of water affect our health?

Answer:

The pH of drinking water should be ranging from 6.5 to 9.2 as recommended by WHO. If the pH of water exceeds the upper limit, then it may cause burning sensation in eyes, skin and mucous membrane.

Water having a pH value more than 11 is very harmful to eyes and skin. If pH of water is in the range of 10-12.5, then it may cause inflation of hair fibres and reduce our digestive capacity.

When pH of water is less than 4, it causes redness and burning sensation in eyes. If pH of water is less than 2.5, it causes extensive and irreparable damage to our skin. The immunity of animals is also largely dependent on the pH level of water.

Question 17. What is meant by coliform count of water?

Answer:

Coliform Count Of Water Means:-

The number of colonies of coliform bacteria such as E. coli present in 100 mL of a sample of water is known as coliform count of that sample of water.

The coliform count of drinking water should always be zero (0). Water used for bathing or water used in swimming pools should have a coliform count less than 200. Maximum coliform count of water used for navigation or fishing should not be greater than 1000.

Question 18. How water is purified or disinfected before distribution in township?

Answer:

Before distribution in towns, water is disinfected. This disinfection or purification is done by adding chlorine tablets or bleaching powder. This process is called chlorination. Chlorine, by oxidation, destroys the harmful microbes present in water and thus disinfected drinking water.

Question 19. Mention the limitations of purification of water by boiling.

Answer:

The limitations of purification of water by boiling are as follows

1. Though most of the germs are killed at a temperature near the boiling point of water, some germs still remain active at that temperature.
2. Harmful metals and some toxic chemical compounds cannot be removed from water by boiling.
3. Most of the essential minerals present in water are removed by boiling.

Question 20. Write down two advantages of chlorination process.

Answer:

Two advantages of chlorination process are:

1. Application of this process is easier and advantageous.
2. Since chlorine remains in water even after a long time from the time of application, the disinfection property also remains active.

Question 21. Mention two limitations of purification of water by chlorination.

Answer:

Two limitations of purification of water by chlorination are as follows

1. Chlorine reacts with organic substances dissolved in water to form trihalomethanes (THMs) and trihaloacetic acids (TAAs). Among the trihalomethanes, bromoform adversely affects the brain and decreases its efficiency thereby causing drowsiness. Prolonged exposure to bromoform & dibromochloro- methane may cause cancer in liver & kidneys.
2. Chlorine being volatile in nature quickly evaporates from water and mixes with the surrounding air thereby causing air pollution.

Question 22. What are the limitations of purification of water by UV-rays?

Answer:

Two major limitations of purification of water by UV-rays are as follows

1. Water which is to be purified by UV-rays should always be clear and transparent. UV- rays are ineffective in turbid water. If some suspended impurities are present in water, it decreases the penetrating power and thus the efficiency of UV-rays.
2. The effect of UV-rays is temporary. In presence of light, the pathogens again become active in UV-purified water. In chlorinated water, chlorine persists in water long after chlorination is done. So, water .retains its germ-killing capacity.

Question 23. Mention the advantages of purification of water by UV-rays.

Answer:

1. The purification of water by UV-rays is fast and effective. It does not affect the taste or smell of water. So, it is very effective in
   purification of drinking water and water used in food processing industries.
2. Purification of water by this method is safe. As no harmful chemicals are used in this method, there is no chance of pollution.
3. UV-rays are more effective than chlorine in removing viruses from water.

Chapter 4 Matter Water Topic A Role Of Water In Development Of Life And Drinking Water Very Short Answer Type Questions Choose The Correct Answer

Question 1. In SI unit, the specific heat of water is

1. 4200 J • kg^-1 • K^-1
2. 2100 J • kg^-1 • K^-1
3. 6300 J • kg^-1 • K^-1
4. 4500 J • kg^-1 • K^-1

Answer: 1. 4200 J • kg^-1 • K^-1

Question 2. Water is a

1. Non-polar solvent
2. Polar solvent
3. Organic solvent
4. None of these

Answer: 2. Polar solvent

Question 3. An organic compound that dissolves in water is

1. Benzene
2. Alcohol
3. Wax
4. Carbon tetrachloride

Answer: 2. Alcohol

Question 4. An inorganic compound that does not dissolve in water is

1. Sodium chloride
2. Potassium nitrate
3. Calcium carbonate
4. Zinc sulphate

Answer: 3. Calcium carbonate

Question 5. The tendency of a liquid to flow against gravity in a narrow tube is called

1. Surface tension
2. Viscosity
3. Capillary action
4. None of these

Answer: 1. Surface tension

Question 6. The water content in a fully grown human being with respect to his total body weight is almost

1. 65%
2. 30%
3. 40%
4. 10%

Answer: 1. 65%

Question 7. The word ‘coliform’ is related to

1. Bacteria
2. Virus
3. Algae
4. Fungus

Answer: 1. Bacteria

Question 8. pH of a solution indicates the concentration of

1. OH^– ions
2. Cl^– ions
3. H⁺ ions
4. Na⁺ ions

Answer: 3. H⁺ ions

Question 9. pH of an acidic solution is

1. Less than 7
2. More than 7
3. Equal to 7
4. None of these

Answer: 1. Less than 7

Question 10. pH of an alkaline solution is

1. Less than 7
2. More than 7
3. Equal to 7
4. None of these

Answer: 2. More than 7

Question 11. The maximum permissible limit of dissolved oxygen in drinking water (in mg • L^-1) as recommended by WHO is

1. 1-2
2. 4-6
3. 8-10
4. 12-15

Answer: 2. 4-6

Question 12. The maximum permissible limit of dissolved chlorides in drinking water (in mg • L^-1) as recommended by WHO is

1. 100
2. 200
3. 300
4. 250

Answer: 4. 250

Question 13. The maximum permissible limit of dissolved fluorides in drinking water (in mg • L^-1) as recommended by WHO is

1. 1-1.5
2. 11-20
3. 21-30
4. 31-40

Answer: 1. 1-1.5

Question 14. The maximum permissible limit of dissolved arsenic in drinking water (in mg • L^-1) as recommended by WHO is

1. 0.05
2. 0.25
3. 0.5
4. 1

Answer: 1. 0.05

Question 15. Which of the following is used for the purification of water?

1. Infrared rays
2. X-rays
3. Ultraviolet rays
4. Gamma rays

Answer: 3. Ultraviolet rays

Question 16. Chlorination of water is done to

1. Destroy the microbes
2. Precipitate the suspended impurities
3. Improve the taste of water
4. Increase the clarity of water

Answer: 1. Destroy the microbes

Question 17. Which property of water helps to control the temperature of atmosphere?

1. Specific heat
2. Dielectric constant
3. Bad conductivity of heat
4. Polar nature

Answer: 1. Specific heat

Question 18. Specific heat of which of the following liquids is the highest?

1. Water
2. Kerosene
3. Petrol
4. Mercury

Answer: 1. Water

Question 19. Example of a water soluble organic compound is

1. Toluene
2. Acetic acid
3. Xylene
4. Chloroform

Answer: 2. Acetic acid

Question 20. Example of universal solvent is

1. Water
2. Kerosene
3. Benzene
4. Alcohol

Answer: 1. Water

Question 21. Value of the dielectric constant of water is

1. 79.4
2. 80.4
3. 81.4
4. 82.4

Answer: 2. 80.4

Question 22. The temperature range where the anomalous expansion of water can be seen

1. 4°C-8°C
2. 0°C-10°C
3. 0°C-4°C
4. 0°C-2°C

Answer: 3. 0°C-4°C

Chapter 4 Matter Water Topic A Role Of Water In Development Of Life And Drinking Water Answer In Brief

Question 1. What is meant by the statement—’Specific heat of water is 1 cal • g^-1 • °C^-1?

Answer: The above statement means that leal of heat is required to raise the temperature of 1 g of pure water by 1°C.

Question 2. At what temperature, the density of water is maximum?

Answer: The density of water is maximum at 4°C (1 g – cm^-3).

Question 3. What is a capillary tube?

Answer: A capillary tube is a long and thin tube made of rigid materials like glass or plastic. The diameter of a capillary tube generally ranges from 0.5 mm to 3 mm.

Question 4. Which property of water makes it a coolant for different machinery used in the industries?

Answer: High specific heat of water makes it an excellent coolant for different machinery used in the industries.

Question 5. Give an example of a covalent compound which is soluble in water.

Answer: Hydrogen chloride (HCI) is a covalent compound which is soluble in water.

Question 6. Give an example of a covalent compound which is insoluble in water.

Answer: Benzene (C₆H₆) is a covalent compound which is insoluble in water.

Question 7. What must be the coliform count of drinking water?

Answer: The coliform count of drinking water must be zero (0).

Question 8. What is meant by the statement—’Coliform count of a sample of water is zero’?

Answer: The above statement means that the sample of water does not contain any colony of coliform bacteria (Escherichia coli).

Question 9. What is the value of dielectric constant of water?

Answer: The value of dielectric constant of water is 80.4.

Question 10. How can water be purified without using any chemicals?

Answer: Water can be purified by using ultraviolet rays (UV-rays) as no chemicals are required in this method.

Question 11. Which halogen is used for the purification of water?

Answer: The halogen used for the purification of water is chlorine.

Question 12. Name two absorbents of water.

Answer: Concentrated sulphuric acid (H₂SO₄) and anhydrous calcium chloride (CaCI₂) are two absorbents of water.

Question 13. How does chlorine destroy the microbes present in water?

Answer: Chlorine destroys the microbes present in water by the process of oxidation.

Question 14. How pH of water changes with increase in temperature?

Answer: pH of water generally decreases with increase in temperature.

Question 15. Give an example of coliform bacteria?

Answer: E.coli.

Question 16. Why chlorination of water is done?

Answer: To destroy the microbes present in water.

Question 17. What should be the permissible limit of oxygen in drinking water as per order of WHO?

Answer: 4-6 mg – L^-1

Question 18. Give the formula of heavy water?

Answer: The formula of heavy water is D₂O

Question 19. For which property, water can be used for cooking purposes?

Answer: Boiling point of water is comparatively higher, that is why it is used for cooking.

Question 20. What type of harm occur if pH of drinking water becomes more than 10.5?

Answer: It causes disturbances in digestion.

Question 21. What type of harm occur if the pH of drinking water becomes less than 4?

Answer: It causes damages of nervous system, lungs, and respiratory tracks and also disturbs the digestion system.

Question 22. How the surgical apparatus and instruments are disinfected?

Answer: The surgical instruments are boiled at a higher temperature more than 100°C, at a higher pressure in autoclave and thus disinfected.

Question 23. For which property of water, different types of salt dissolve in it?

Answer: For polar nature of water molecule.

Question 24. Due to which physical property of water, the water bodies like ponds and lakes do not freeze immediately on a cold day in winter- countries?

Answer: Latent heat of solidification of water has a higher value (336 J/g). This property of water helps in the mentioned process.

Chapter 4 Matter Water Topic A Role Of Water In Development Of Life And Drinking Water Fill In the Blanks

Question 1. Specific heat of water is ________ than ice.

Answer: Greater

Question 2. Water is a ________ solvent.

Answer: Polar

Question 3. Water absorbed by the roots of plants reach the leaves through stem due to __________

Answer: Capillary

Question 4. __________ is generally used to precipitate the impurities suspended in water.

Answer: Alum

Question 5. Only __________ % of total water content found on the earth’s surface is usable.

Answer: 1

Question 6. pH is the negative logarithm of ______ ion concentration of a solution.

Answer: Hydrogen

Question 7. pH of pure water is __________

Answer: 7

Question 8. UV-rays destroy the ________ present in water.

Answer: Microbes

Question 9. Taste of water depends on the amount of ________ dissolved in it.

Answer: Salts

Question 10. Purification of water by boiling also leads to the removal of essential _________ dissolved in water.

Answer: Minerals

Question 11. __________ % of total water content on the earth’s surface constitutes of sea water.

Answer: 97

Question 12. The latent heat required for solidification of water is ___________ J • g^-1

Answer: 336

Question 13. The permissible range of pH value of drinking water is ______

Answer: 6.5-8.5

Question 14. Purification of water by ______ radiation is not effective for turbid water.

Answer: Ultraviolet

Question 15. Chlorine reacts with organic materials present in water to produce _______ and _______

Answer: Trichloromethane, trihaloacetic acid

Question 16. The approved level of dissolved oxygen in drinking water, as per WHO recommendation, is ________ mg • L^-1.

Answer: 4-6

Question 17. The admissible level of fluoride in drinking water as per WHO norms is ________ mg • L^-1.

Answer: 1

Chapter 4 Matter Water Topic A Role Of Water In Development Of Life And Drinking Water State Whether True Or False

Question 1. The pH of drinking water should range between 4.5 to 6.5.

Answer: False

Question 2. The coliform count of drinking water must be zero.

Answer: True

Question 3. Chlorination is an effective method for removing permanent hardness of water.

Answer: False

Question 4. The density of water is minimum at 0°C.

Answer: False

Question 5. Consumption of deionised water is good for the human body.

Answer: False

Question 6. Fluoride salts can be eliminated from water by passing through activated alumina.

Answer: True

Question 7. Distilled water is less pure than deionised water.

Answer: False

Question 8. Water is used as a coolant because of its low value of specific heat.

Answer: False

Question 9. Magnesium reacts with water at ordinary temperature.

Answer: False

Question 10. Capillary action of water is responsible for the absorption of water by roots and its subsequent transportation to the leaves.

Answer: True

Question 11. Specific heat of water is the highest among known liquids.

Answer: True

Question 12. The colloidal substance floating in water gets precipitated on addition of alum.

Answer: True

Question 13. The density of water at 4°C is lower than that at 0°C.

Answer: False

Question 14. Drinking water can be disinfected by boiling.

Answer: True

Chapter 4 Matter Water Topic B Soft Water And Hard Water Synopsis

1. Water that does not produce lather with soap, or does so only if large amount of soap is used is called hard water. On the other hand, soft water easily produces lather or foam with soap.
2. Hardness of water which can be removed by simple processes like boiling is called temporary hardness. On the other hand, hardness of water which cannot be removed by boiling is called permanent hardness.
3. Presence of chloride or sulphate salts of calcium, magnesium and iron cause permanent hardness of water. Bicarbonates of these metals produce temporary hardness in water.
4. Presence of Zn-salts or Al-salts also causes hardness of water. However, salts of alkali metals like sodium or potassium are not responsible for hardness of water.
5. Temporary hardness of water can be removed by boiling, while ion-exchange resin method removes both temporary and permanent hardness of water.
6. A sample of water that does not contain any ions other than H⁺ and OH^– ions is called
   deionised water.

Chapter 4 Matter Water Topic B Soft Water And Hard Water Short And Long Answer Type Questions

Question 1. What is meant by hard water and soft water? Give examples.

Answer:

Hard water: The type of water that barely produces lather with soap or does so after consuming a large amount of soap is called hard water. For example, river water, sea water, waterfalls etc., are natural sources of hard water.

Soft water: The type of water that easily forms lather with soap is called soft water. For example, distilled water, deionised water etc.

Question 2. What is the cause of hardness of water? What are the different types of hardness of water?

Answer:

Hardness of water is resulted due to the presence of bicarbonate, sulphate and chloride salts of calcium, magnesium and iron which remain dissolved in water.

On the basis of the nature of dissolved salts, hardness of water is of two types

1. Temporary hardness and
2. Permanent hardness.

Question 3. What do you mean by temporary hardness of water?

Answer:

Hardness produced due to the presence of dissolved bicarbonate salts of calcium and magnesium [Ca(HCO₃)₂ and Mg(HCO₃)₂] and to some extent iron which can be removed by simply boiling the water is known as temporary hardness.

Question 4. What do you mean by permanent hardness of water?

Answer:

Hardness produced due to the presence of dissolved sulphate and chloride salts of calcium, magnesium and iron [CaCl₂, CaSO₄, MgCI₂, MgSO₄, FeSO₄] which cannot be removed by simply boiling the water is called permanent hardness or non-carbonate hardness.

Question 5. Name two processes for the removal of hardness of water.

Answer:

Two processes for the removal of hardness of water are: boiling (Process for removal of temporary hardness) and ion-exchange process (Process for removal of both temporary and permanent hardness of water).

Question 6. Which one of these has the higher probability of being hard: spring water or rain water.

Answer:

Probability of being hard water is more in case of spring water. Water from different water bodies get evaporated and forms cloud in the higher part of sky which when condense, form rain where the minerals remain absent as those were not evaporated at all.

That is why rain water remains soft in nature. On the other hand, spring water flows above rocks and minerals. During this flow the metallic salts, responsible for hardness dissolve in it and make the spring water hard.

Question 7. Temporary hardness of water caused by magnesium bicarbonate cannot be removed completely by boiling. Explain with reason.

Answer:

On boiling hard water (containing magnesium bicarbonate), the soluble bicarbonate decomposes to form water insoluble carbonate salt.

⇒ \(\mathrm{Mg}\left(\mathrm{HCO}_3\right)_2 \rightarrow \mathrm{MgCO}_3 \downarrow+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2 \uparrow\)

As MgCO₃ is sparingly soluble in water, temporary hardness of water caused by magnesium bicarbonate cannot be removed completely by boiling.

Question 8. How is the degree of hardness of water expressed?

Answer:

Degree of hardness of water is defined as the number of parts by mass of calcium carbonate (CaCO₃) equivalent to various calcium and magnesium salts present in one million (10⁶) parts by mass of water. Degree of hardness of water is expressed in terms of ppm (parts per million).

Question 9. What do you mean by the statement— ‘Hardness of a sample of water is 300 ppm’?

Answer:

The above statement means that 300 parts by mass of calcium carbonate equivalent to various salts causing hardness of water is present in one million parts by mass of that water sample.

Question 10. Mention two disadvantages of using hard water.

Answer:

1. Hard water can not be used in cooking as the food particles are not boiled properly in hard water.
2. Hard water is not suitable for drinking as it affects the digestive system.

Question 11. Why does normal water behave as hard water if few drops of mineral acid are added to it?

Answer:

If few drops of mineral acids like HCI or H₂SO₄ are added to normal water, then it behaves as hard water because the acid react with soaps to precipitate insoluble fatty acids.

This is why soaps do not produce lather in this type of water.

Question 12. Describe the boiling processj of temporary hardness of water?

Answer:

When the temporary hard water is boiled, the soluble bicarbonates converted to insoluble carbonates and precipitated out. After filtration one can get the hardness freed water.

⇒ \(\mathrm{Ca}\left(\mathrm{HCO}_3\right)_2 \rightarrow \mathrm{CaCO}_3 \downarrow+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2 \uparrow\)

⇒ \(\mathrm{Mg}\left(\mathrm{HCO}_3\right)_2 \rightarrow \mathrm{MgCO}_3 \downarrow+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2 \uparrow\)

Question 13. Why do soaps not produce lather with hard water initially?

Answer:

Soaps are sodium or potassium salts of fatty acids having high molecular mass (e.g. stearic acid, palmitic acid, oleic acid etc.) which dissolve in water to form lather.

However, calcium and magnesium salts of these fatty acids are insoluble in water and do, not produce lather. Calcium and magnesium salts remain dissolved in hard water.

When these metal cations react with soap, initially a white precipitate is formed which is actually the insoluble calcium and magnesium salts of those fatty acids. Lather is produced only when all the Ca²⁺ and Mg²⁺ ions present in water are completely precipitated

Question 14. What are cation exchange resins?

Answer:

A cation exchange resin is an artificially synthesised organic polymer having a complex network structure in which an acidic group, — SO₃H (sulphonic acid) is attached to a large hydrocarbon chain. The general formula of a cation exchange resin is R —SO₃H.

Question 15. What are anion exchange resins?

Answer:

An anion exchange resin is an artificially synthesised organic polymer having a complex network structure in which an alkaline OH^– group is present as substituted ammonium hydroxide attached to a large hydrocarbon chain. The general formula of a anion exchange resin is R — \(\mathrm{NH}_3^{+} \mathrm{OH}^{-}\).

Question 16. Resins used in the ion exchange method become inactive after prolonged use. How are they regenerated?

Answer:

The inactive cation exchange resins are reactivated by passing dilute H₂SO₄ or dilute HCI through the resin layers.

[M = Ca, Mg; R = alkyl radicals]

Similarly, the inactive anion exchange resins are reactivated by passing dilute NaOH solution through the resin layers.

Question 17. Why is demineralised water or distilled water not suitable for drinking? How can one make this water suitable for drinking?

Answer:

Calcium, magnesium and iron salts are very essential for the growth and development of living organisms. As these salts are absent in demineralised water or distilled water, it is not suitable for drinking although being very pure in nature.

Demineralised or distilled water can be made suitable for drinking by adding essential minerals in proportionate amounts.

Question 18. What is deionised water? Between distilled water and deionised water, which one is purer and why?

Answer:

Water obtained by consecutively treating it with cation exchange resin and anion exchange resin is free from all ions except H⁺ ions and OH^– ions. This is known as deionised water.

Deionised water is free from all ions. Hence, it is soft water. However, this water may contain, (apart from H⁺ and OH^– ions) some organic impurities, dissolved gases and even germs.

On the other hand, water obtained by distillation is free from ions as well as organic impurities, dissolved gases and germs. Hence, distilled water is purer than deionised water.

Question 19. Explain why distilled water is not suitable for drinking.

Answer:

Calcium, magnesium and iron salts all are very essential elements for living bodies. Demineralised or distilled water do not contain any of such salts.

That is why demineralised or distilled water is not suitable for drinking. By mixing the essential minerals in definite proportions distilled water can be converted to drinking water.

Question 20. Explain why deionised water is not used for injections.

Answer:

Some organic impurities or some microbes may present in deionised water. That is why deionised water is not used for injections.

Question 21. Differentiate between deionised water and distilled water.

Answer:

The difference between deionised water and distilled water are:

Chapter 4 Matter Water Topic B Soft Water And Hard Water Vert Short Answer Type Questions Choose The Correct Answer

Question 1. If hardness of water increases, then it

1. Can easily produce lather
2. Cannot produce lather
3. Can produce lather only by consuming large amount of soap
4. None of these

Answer: 3. Can produce lather only by consuming large amount of soap

Question 2. The hardness of water can be of

1. 4 types
2. 3 types
3. 2 types
4. 5 types

Answer: 3. 2 types

Question 3. A salt responsible for permanent hardness of water is

1. CaCl₂
2. Ca(HCO₃)₂
3. NaCI
4. Na₂CO₃

Answer: 1. CaCl₂

Question 4. A salt responsible for temporary hardness of water is

1. CaCI₂
2. Ca(HCO₃)₂
3. NaCI
4. Na₂CO₃

Answer: 2. Ca(HCO₃)₂

Question 5. If acid (H⁺) is added to water, then water will behave as

1. Soft water
2. Hard water
3. Pure water
4. Deionised water

Answer: 2. Hard water

Question 6. Boiling can be used to

1. Remove permanent hardness of water
2. Deionise water
3. Remove temporary hardness of water
4. Decolourise water

Answer: 3. Remove temporary hardness of water

Question 7. The general formula of cation exchange resins is

1. R —OH
2. R — SO₃H
3. R —Cl
4. R —NH₂

Answer: 2. R — SO₃H

Question 8. The general formula of anion exchange resins is

1. R —Cl
2. R — COOH
3. R — NH₃⁺OH^–
4. R —H

Answer: 3. R — NH₃⁺OH^–

Question 9. Cation exchange resins are regenerated by using a dilute solution of

1. NaOH
2. HCI
3. NaCl
4. Na₂SO₄

Answer: 2. HCI

Question 10. Anion exchange resins are regenerated by using a dilute solution of

1. NaOH
2. HCI
3. NaCl
4. Na₂SO₄

Answer: 1. NaOH

Question 11. Degree of hardness of water is measured in

1. g • L^-1
2. mol • L^-1
3. ppm
4. kg • L^–

Answer: 3. ppm

Question 12. The type of water used in boilers of factories is

1. Soft water
2. Hard water
3. Deionised water
4. Germ-free water

Answer: 1. Soft water

Question 13. Which of the following happens when hardness of water increases?

1. Lather forms easily
2. Lather does not form at all
3. Lather forms after rubbing the soap for a long time
4. None of the above

Answer: 3. Lather forms after rubbing the soap for a long time

Question 14. Hardness of deionised water is

1. 0
2. 1
3. 3
4. 7

Answer: 1. 0

Question 15. pH of deionised water is

1. 0
2. 2
3. 4
4. 7

Answer: 4. 7

Question 16. Which of the following cations is present in deionised water?

1. H⁺
2. Na⁺
3. Mg²⁺
4. Ca²⁺

Answer: 1. H⁺

Question 17. Which of the following ions is not responsible for hardness of water?

1. Ca²⁺
2. Mg²⁺
3. Fe²⁺
4. Na⁺

Answer: 4. Na⁺

Question 18. Which of the following processes can remove temporary and permanent hardness of water simultaneously?

1. Boiling
2. Chlorination
3. U.V. ray
4. Ion-exchange process

Answer: 4. Ion-exchange process

Question 19. Which of the following ions is absent in hard water?

1. Carbonate
2. Bicarbonate
3. Chloride
4. Sulphate

Answer: 1. Carbonate

Question 20. In deionised water

1. No ion is present
2. Only H⁺ ion is present
3. Only OH⁺ ion is present
4. Both H⁺ ion and OH^– ion is present

Answer: 4. Both H⁺ ion and OH^– ion is present

Question 21. Which of the following is used for injection?

1. Soft water
2. Hard water
3. Deionised water
4. Distilled water

Answer: 4. Distilled water

Chapter 4 Matter Water Topic B Soft Water And Hard Water Answer In Brief

Question 1. What is the working principle of pressure cooker?

Answer:

In a pressure cooker, the steam, so produced increases the pressure above the surface of water. As a result, water boils at higher temperature than its normal boiling point due to elevation of boiling point. As a result, food gets boiled properly and rapidly.

Question 2. Hard water is suitable for washing clothes’— Is the statement right or wrong?

Answer: When hard water is used, large amount of soap is required to produce lather which results in wastage of soap. Hence, hard water is not suitable for washing clothes.

Question 3. Name two metals that react with water at room temperature.

Answer: Sodium (Na) and calcium (Ca) react with water at room temperature.

Question 4. Name a salt which causes temporary hardness in water.

Answer: Calcium bicarbonate [Ca(HCO₃)₂] causes temporary hardness in water.

Question 5. Name a sulphate salt responsible for permanent hardness in water.

Answer: Magnesium sulphate (MgSO₄) causes permanent hardness in water.

Question 6. What is meant by reversibility of resins?

Answer: Salts are formed due to exchange of H⁺ and OH^– ions of the resins with the cations and anions present in hard water. The activity of resins can be regenerated by treating these salts with dilute acid or alkali solutions. This is known as reversibility of resins.

Question 7. Name a fatty acid from which soap is prepared.

Answer: A fatty acid from which soap is prepared is stearic acid.

Question 8. Which type of hardness can be removed by boiling?

Answer: Temporary hardness of water caused by bicarbonate salts of calcium and magnesium can be removed by boiling the water.

Question 9. State if aquatic organisms can survive in distilled water or not.

Answer: No, aquatic organisms cannot survive in distilled water due to lack of dissolved oxygen in it.

Question 10. Which part of a salt is responsible for causing hardness of water?

Answer: The cation of a salt is responsible for causing hardness of water.

Question 11. Two samples of water contain dissolved Zn- salts and Na-salts respectively. Which one is hard water?

Answer: Zn-salts cause hardness of water. Hence, the sample having dissolved Zn-salt in it will be hard water.

Question 12. Which method is effective in removing all types of hardness of water?

Answer: Ion-exchange method is effective in removing all types of hardness of water.

Question 13. By which process permanent hardness of water can be removed?

Answer: Ion exchange process.

Question 14. Which ions are present in deionised water?

Answer: H⁺ and OH^– ions are present in deionised water.

Question 15. If or whenever the efficiency of the cation exchange resin reduces, what should be passed through them to regain the efficiency?

Answer: It Dilute H₂SO₄ or dilute HCI is passed though the resin layer.

Question 16. Which type of hardness is removed by ion exchange process?

Answer: Both temporary and permanent hardness are removed.

Question 17. Name a calcium salt, responsible for hardness of water.

Answer: Calcium sulphate (CaSO₄).

Question 18. Name a magnesium salt, responsible for temporary hardness.

Answer: Magnesium bicarbonate [Mg(HCO₃)₂].

Question 19. NaCI and K₂SO₄ are dissolved is a sample of water. Mention whether it is soft or hard water.

Answer: Soft water.

Question 20. Name a halogen whose water-soluble salts cause water pollution.

Answer: Fluorine causes water pollution as it remains in water as soluble fluoride salts.

Chapter 4 Matter Water Topic B Soft Water And Hard Water Fill In The Blanks

Question 1. Cation exchange resins are organic _______ acids having high molecular mass.

Answer: Sulphonic

Question 2. ________ is a useful method for the removal of permanent hardness of water.

Answer: Ion-exchange

Question 3. If the hardness of water increases, then the amount of soap required to form lather in that water also _________

Answer: Increases

Question 4. It is preferable to use _________ over soap in hard water.

Answer: Detergents

Question 5. Detergents can produce lather even in ______ water.

Answer: Hard

Question 6. Water after treating with cation exchange resin is ________ in nature.

Answer: Acidic

Question 7. Permanent hardness is also known as ________ hardness.

Answer: Non-carbonate

Question 8. Temporary hardness is also known as __________ hardness.

Answer: Carbonate

Question 9. Efficiency of anion exchange resin is regained by passing ________ solution.

Answer: NaOH

Question 10. _________ hardness cannot be removed by boiling.

Answer: Permanent

Question 11. _______ water should be used for cooking.

Answer: Soft

Chapter 4 Matter Water Topic B Soft Water And Hard Water State Whether True Or False

Question 1. The hardness which can be removed by simply boiling the water is known as permanent hardness.

Answer: False

Question 2. Both temporary and permanent hardness of water can be removed by using ion-exchange resin.

Answer: True

Question 3. The cationic part of a salt is responsible for imparting hardness to water.

Answer: True

Question 4. Spring water is the example of soft water.

Answer: True

Question 5. Water will be hard if Na or K-salt are present in it.

Answer: False

Question 6. Hardness of distilled water is zero.

Answer: True

Question 7. Deionised water is completely pollution free.

Answer: False

Question 8. Deionised water is used for injections.

Answer: False

Chapter 4 Matter Water Topic C Water Pollution Synopsis

1. Detergents, pesticides and chemical fertilisers dissolve in water and cause extensive water pollution.
2. The presence of excess phosphate salts in water causes eutrophication (rapid increase in aquatic plant population) in water bodies. On the other hand, The presence of excess nutrients in water causes rapid increase in population of algae and the entire surface of water gets covered by algae. This phenomenon is known as algal bloom.
3. Undesired changes in human beings, other living organisms and environment due to arsenic contamination of water is called arsenic pollution. It may cause several health related problems in man and other animals. The maximum permissible limit (as per WHO guidelines) of arsenic in drinking water is 0.05 mg -L^-1.
4. Excess arsenic enters into the human body through drinking water and may lead to black foot disease.
5. Undesired changes in human beings, other living organisms and the environment due to the contamination of water by fluoride salts is called fluoride pollution. The maximum permissible limit (as per WHO guidelines) of fluorides in drinking water is 1.10 mg • L^-1.
6. Fluoride pollution of water causes dental fluorosis.
7. Water is made arsenic-free by different methods such as adsorption, coprecipitation, ion-exchange method, reverse osmosis etc.
8. Fluoride salts are removed from water by passing the water through activated alumina columns.

Chapter 4 Matter Water Topic C Water Pollution Short And Long Answer Type Questions

Question 1. What is meant by water pollution?

Answer:

Water Pollution:-

Undesired changes in the physical, chemical or biological parameters of water that results in contamination of water bodies thus, making it unsafe for living organisms (both terrestrial and marine) is called water pollution.

Question 2. Mention three major causes water pollution.

Answer:

Major Causes Water Pollution:-

Three major causes of water pollution are as follows

1. Disposal of domestic wastes like detergents, plastics etc., in water bodies.
2. Industrial wastes like oil, grease, acid etc., released in water bodies.
3. Mixing of fertilisers, pesticides and insecticides used in agricultural lands with nearby water bodies.

Question 3. Name two pesticides which cause water pollution. Mention their harmful effects.

Answer:

Harmful Effects Caused By The Pesticides:- 

Two commonly used pesticides which cause water pollution are—DDT (p, p’-dichlorodi- phenyl trichloroethane) and gammaxene.

These pesticides affect the function of brain and may cause cancer (carcinogenic in nature).

Question 4. Discuss how pesticides cause water pollution

Answer:

Pesticides Cause Water Pollution As Follows:-

Pesticides are chemical compounds used to preserve crops from the attacks of insects, fungi etc. (collectively called pests). These pesticides are washed off by water into nearby rivers, ponds, lakes etc. causing water pollution.

Pesticides are mostly non-biodegradable compounds and do not decompose biochemically. These substances enter into the human bodies and other animals through food chain and cause biomagnification.

This leads to headache, nervous breakdown, slackening of muscles, convulsions etc. Prolonged exposure to these substances may even cause tumour or cancer.

Question 5. Discuss how fertilisers cause water pollution.

Answer:

Fertilisers Cause Water Pollution As Follows:-

Fertilisers are chemical compounds used to increase the fertility of soil thereby increasing the yield of crops such as, urea, ammonium sulphate, ammonium nitrate etc. When fertilisers are applied to agricultural fields, these are washed away by water into nearby rivers, ponds, lakes etc. causing water pollution.

Excessive nitrate salts in drinking water may cause methaemoglobinaemia in infants. Presence of excessive phosphate salts results in eutrophication in water bodies.

Question 6. How do nitrate fertilisers cause water pollution?

Answer:

Nitrate Fertilisers Cause Water Pollution As Follows:-

Nitrate fertilisers are widely used in agricultural lands. These salts being soluble in water dissolve in it and are washed away to nearby water bodies. Excess quantity of these salts act as pollutants rather than nutrients.

If excess quantity of nitrate salts enter the body through consumption of drinking water, it may cause methaemoglobinaemia in infants. It can also interfere with the ability of red blood corpuscles to transport oxygen to different parts of the body thereby disrupting physiological processes like circulation and respiration.

Question 7. What are detergents? What is the advantage of using detergents in hard water?

Answer:

Detergents And Advantage Of Using Detergents In Hard Water:-

Detergents are artificially synthesised mixtures of two or more substances which have cleansing properties. A detergent contains two major components

1. A surface active substance (like, alkyl benzene sulphonate) and
2. A builder or filler (like sodium tripolyphosphate).
3. Detergents can produce lather or foam even in hard water causing less wastage.

Question 8. Discuss how detergents cause water pollution.

Answer:

Detergents Cause Water Pollution As Follows:-

Detergents are the major water pollutants. They cause water pollution in the following ways

1. Lather produced by detergents accumulate on the surface of water thereby preventing air and sunlight from entering into the depths of water. Consequently, dissolved oxygen of water decreases.
2. Detergents contain surface-active compounds which form layers on the organic pollutants present in water and prevent their biochemical decomposition. This increases the pollution level of water.
3. Phosphate compounds are used as fillers in detergents. These phosphate compounds cause eutrophication.

Question 9. What is eutrophication?

Answer:

Eutrophication:-

The phenomenon of rapid growth in the population of aquatic plants (mainly algae) in water bodies due to enrichment of water with excess phosphate fertilisers, phosphate compounds of detergents etc. (which act as nutrients) is known as eutrophication.

Question 10. Discuss the harmful effects of eutrophication.

Answer:

Harmful Effects Of Eutrophication:-

1. Due to rapid population growth of aquatic plants, demand of oxygen for their respiration also increases.
2. Thus, amount of dissolved oxygen in water decreases rapidly thereby threatening the survival of aquatic life.
3. Rapid decrease in the amount Of dissolved oxygen in water leads to an abnormal increase in population of anaerobic bacteria. These bacteria acts on the different organic and inorganic waste materials present in water to produce gases such as, methane, ammonia, hydrogen sulphide etc. which leads to emission of foul smell in water.

Question 11. What is algal bloom? Mention its effects.

Answer:

Algal Bloom And Its Effects:-

1. The rapid increase in the population of algae due to presence of excess nutrients in stagnant water bodies is known as algal bloom.
2. Due to this increased population growth of algae, the surface of water gets entirely covered with algae. This prevents sunlight from reaching the depths of the water body.
3. The level of dissolved oxygen also decreases rapidly due to algal bloom. Due to insufficient oxygen, aquatic plants and animals die which disrupts the overall functioning of aquatic ecosystem. Apart from this, bacterial decom-position of dead plants and animals in the water body makes it more polluted.

Question 12. What is arsenic pollution? Is the element arsenic directly responsible for arsenic pollution?

Answer:

Arsenic Pollution:-

The undesired effects on living beings (mainly human beings) caused due to the presence of arsenic compounds in water, in an amount greater than the permissible limit, is known as arsenic pollution.

No, the element arsenic is not directly responsible for arsenic pollution. Presence of certain arsenic salts like arsenate and arsenite in water causes arsenic pollution in water.

Question 13. Mention one natural and one artificial reason for arsenic pollution.

Answer:

Natural And Artificial Reason For Arsenic Pollution:-

Natural Reason: Insoluble layer of arsenic compounds are present in contact with the groundwater layer. Excessive use of this groundwater helps air to come in contact with this insoluble salts. As a result soluble arsenite and arsenate salts are produced which is the main cause of arsenic pollution in water.

Artificial Reason: Different arsenic-containing compounds e.g., sodium arsenite, lead arsenate, calcium arsenate etc. are used as antifungal and pesticidal substance. They are when dissolved in water make the water polluted.

Question 14. Discuss the harmful effects of arsenic pollution on human beings.

Answer:

Harmful Effects Of Arsenic Pollution On Human Beings:-

1. Consumption of water containing arsenic disturbs the blood circulation in our body.
2. It makes the skin rough and black patches appear on the skin in the neck, shoulder and back region of the body. Long term exposure to arsenic salts may cause black-foot disease which causes appearance of black spots on palms and feet.
3. Consumption of water containing arsenic for a long time may lead to cirrhosis of liver and even cancer in lungs and intestine.

Question 15. Mention any two processes.

Answer:

Two Processes:-

Adsorption Method: Both the salts of arsenic that cause pollution i.e., arsenate and arsenite, are adsorbed by activated alumina (Al₂O₃).So tube wells are fitted with columns of alumina to remove arsenic from water.

Co-Precipitation Method: If alum and hydrated ferric oxide are added to water and left undisturbed for a long period of time, then the arsenic-containing compounds gradually settle down at the bottom and are separated from water by filtration.

Question 16. In which state chlorine, fluorine and arsenic are present in natural water?

Answer:

Chlorine: Chlorine is found in natural water in elemental state (Cl₂), as hypochlorous acid (HOCI), as hypochloride salts and chloride salts dissolved in water.

Fluorine: Fluorine remains dissolved in natural water as fluoride salts.

Arsenic: In natural water, arsenic is found as soluble inorganic salts, arsenite (AsO₃^3-) and arsenate (AsO₄^3-) and as soluble organoarsenic compound, cacodylic acid [(CH₃)₂AsO₂H].

Question 17. What is the maximum permissible limit of fluorides in drinking water? Discuss the harmful effects of excess fluorides in drinking water.

Answer:

As recommended by WHO, the maximum permissible limit of fluoride salts in drinking water is 1.5 mg • L^-1.

The presence of 1.0 mg • L^-1 of fluoride salts in drinking water is essential as it prevents the decay of tooth enamel. However, if the amount of fluoride salts slightly exceeds this permissible limit, then it may cause dental fluorosis and if the amount largely exceeds the permissible limit, then it may lead to osteoporosis.

Question 18. How is dissolved fluoride salts removed from water?

Answer:

Methods Of Removal of fluorides from water are:-

1. If water contains large quantities of fluoride salts, then it is passed over activated alumina to eliminate fluoride salts.
2. Water containing fluoride salts is treated with potash alum and lime and is kept undisturbed for some hours. The fluoride salts settle down and is then removed by filtration.

Chapter 4 Matter Water Topic C Water Pollutoin Very Short Answer Type Questions Choose The Correct Answer

Question 1. The type of salt responsible for algal bloom in water is

1. Chloride
2. Arsenic
3. Phosphate
4. Fluoride

Answer: 2. Arsenic

Question 2. DDT is used as a

1. Fertiliser
2. Detergent
3. Pesticide
4. Soap

Answer: 3. Pesticide

Question 3. Which of the following is not a water-borne disease?

1. Typhoid
2. Cholera
3. Malaria
4. Jaundice

Answer: 3. Malaria

Question 4. The quantity of oxygen (in mg) required for complete oxidation of the dissolved organic substances in 1 litre of water is known as

1. AOD
2. BOD
3. COD
4. DOD

Answer: 2. BOD

Question 5. The value of COD is generally

1. Equal to BOD
2. Less than BOD
3. Greater than BOD
4. None of these

Answer: 3. Greater than BOD

Question 6. Degree of hardness of deionised water is

1. 0
2. 2
3. 4
4. 7

Answer: 1. 0

Question 7. Which of the following is caused in human body due to arsenic pollution in water?

1. Decay of tooth enamel
2. Black patches on the skin of mainly feet and palms
3. Methaemoglobinaemia
4. Typhoid

Answer: 2. Black patches on the skin of mainly feet and palms

Question 8. What type of salt present in water causes dental erosion?

1. Chloride
2. Bromide
3. Iodide
4. Fluoride

Answer: 4. Fluoride

Question 9. Which class of compounds present in detergents is responsible for causing water pollution?

1. Sulphates
2. Chlorides
3. Phosphates
4. Carbonates

Answer: 3. Phosphates

Question 10. Soap is a

1. Calcium salt of fatty acids having high molecular mass
2. Sodium salt of fatty acids (organic acid) having high molecular mass
3. Aluminium salt of fatty acids having low molecular mass
4. Magnesium salt of fatty acids having high molecular mass

Answer: 2. Sodium salt of fatty acids (organic acid) having high molecular mass

Question 11. In which of the following districts of West Bengal, arsenic contamination of groundwater is maximum?

1. Purulia
2. Darjeeling
3. West Midnapore
4. Murshidabad

Answer: 4. Murshidabad

Question 12. Which of the following is not responsible for fluoride pollution of groundwater?

1. Cryolite
2. Fluorapatite
3. Fluorspar
4. Sodium fluoride

Answer: 4. Sodium fluoride

Question 13. Which of the following methods is used to control arsenic pollution?

1. Adsorption method
2. Co-precipitation method
3. Ion-exchange method
4. All of these

Answer: 4. All of these

Question 14. Cause of minamata disease is

1. Arsenic pollution
2. Fluoride pollution
3. Mercury pollution
4. Phosphate pollution

Answer: 3. Mercury pollution

Question 15. Which one is the purest form?

1. De-ionised water
2. Distilled water
3. Rain water
4. Tubewell water

Answer: 2. Distilled water

Question 16. Which of the following is formed when chlorine reacts with water?

1. HOCI
2. HCI
3. Nascent oxygen
4. All of the above

Answer: 4. All of the above

Question 17. Black-foot disease is caused by

1. \(\mathrm{NO}_3^{-}\)
2. \(\mathrm{AsO}_3^{3-}\)
3. \(\mathrm{PO}_4^{3-}\)
4. F^–

Answer: 2. \(\mathrm{AsO}_3^{3-}\)

Question 18. Which one of the following is the process for removal of fluoride pollution?

1. Passing through Al₂O₃ column
2. Addition of lime and alum
3. Co-precipitation process
4. All of the above

Answer: 4. All of the above

Question 19. The disease caused due to drinking of water containing nitrate ions is

1. Black-foot disease
2. Itai-itai
3. Methamoglobinemia
4. Fluorosis

Answer: 3. Methamoglobinemia

Question 20. Which of the following reduces in water as a result of eutrophication?

1. Dissolved hydrogen
2. Dissolved oxygen
3. Dissolved nitrate
4. Dissolved minerals

Answer: 2. Dissolved oxygen

Question 21. Which of the following is present in the toxic chemicals excreted from paper industry?

1. Cd
2. Hg
3. Pb
4. Nitrate

Answer: 2. Hg

Question 22. Itai-itai disease is caused by

1. Mercury pollution
2. Phosphate pollution
3. Cadmium pollution
4. Sulphate pollution

Answer: 3. Cadmium pollution

Question 23. Which of the following medium is polluted mostly by arsenic?

1. Air
2. Water
3. Soil
4. All of the above

Answer: 2. Water

 

Chapter 4 Matter Water Topic C Water Pollutoin Answer In Brief

Question 1. Name three metals pollutants present in industrial wastes.

Answer: Cadmium (Cd), mercury (Hg) and lead (Pb).

Question 2. Name a pesticide that causes water pollution.

Answer: DDT (p, p’-dichlorodiphenyltrichloroethane) is a pesticide that causes water pollution.

Question 3. Which type of fertiliser present in water may cause methaemoglobinaemia in children?

Answer: Presence of nitrate fertilisers in water may cause methaemoglobinaemia in children.

Question 4. Which type of fertiliser is responsible for causing algal bloom in water bodies?

Answer: Mainly phosphate fertilisers are responsible for causing algal bloom in water bodies.

Question 5. State whether eutrophication increases or decreases the amount of dissolved oxygen in water.

Answer: Eutrophication decreases the amount of dissolved oxygen in water.

Question 6. What is the full form of BOD?

Answer: BOD stands for Biochemical Oxygen Demand (or Biological Oxygen Demand).

Question 7. What is the permissible value of BOD for pure water?

Answer: The permissible value of BOD for pure water is 5 ppm.

Question 8. What does a high value of BOD of water indicate?

Answer: A high value of BOD of water indicates the presence of large amount of organic pollutants in water.

Question 9. Waste water released from a factory has a pH value less than 3.7—From this given statement, what can you conclude about the quality of the waste water?

Answer: The waste water released from the factory is highly acidic in nature and thus, will cause water pollution.

Question 10. What are the major causes of thermal pollution of water?

Answer: Hot water released from the thermal power plants, oil refineries and other industries mixes with the nearby water bodies to cause thermal pollution.

Question 11. Presence of which metal in drinking water causes Minamata disease?

Answer: The presence of mercury or mercury containing compounds in drinking water causes Minamata disease.

Question 12. Name a disease caused due to fluoride pollution of water.

Answer: Dental fluorosis is a disease caused due to fluoride pollution of water.

Question 13. Name a disease caused due to arsenic pollution of water.

Answer: Black foot disease is caused due to arsenic pollution of water.

Question 14. Name a pesticide that contains arsenic.

Answer: Lead hydrogen arsenate (PbHAsO₄) is an inorganic pesticide that contains arsenic.

Question 15. Name a metal ore found in the earth’s crust that contains arsenic.

Answer: Arsenopyrites (FeAsS) is an ore of iron that contains arsenic and is found in the earth’s crust.

Question 16. Which soluble salts are produced when water insoluble arsenic compounds present in the earth’s crust react with air?

Answer: When water insoluble arsenic compounds present in the earth’s crust react with air, soluble arsenate and arsenate salts are produced.

Question 17. Which substance is used as the semiper- meable membrane during removal of arsenic from water by reverse osmosis?

Answer: During removal of arsenic from water by reverse osmosis method, cellulose triacetate is used as the semipermeable membrane.

Question 18. What amount of arsenic in blood may cause arsenicosis?

Answer: If blood contains more than 60μg • L^-1 of arsenic, then it may cause arsenicosis.

Question 19. What is biological magnification?

Answer: Biological magnification or biomagnification is a phenomenon by which the toxic chemical substances (such as DDT, aldrin which are generally not decomposed by biochemical reactions) are continuously deposited in the fat-tissues of living organisms through intake of food (food chain).

Question 20. Which pollutant present in drinking water causes anemia?

Answer: Nitrate (\(\mathrm{NO}_3^{-}\)) causes anaemia.

Question 21. What is the reason behind knock-knee syndrome?

Answer: consumption of fluoride (F^–) contaminated water for a long period of time causes knock- knee syndrome.

Question 22. Which ores are responsible for fluoride pollution of drinking water?

Answer: Fluorapetite [3Ca₃(PO₄)₂ • CaF₂],fluospar (CaF₂) and cryolyte (Na₃AIF₆).

Question 23. Which disease is caused by Arsenic Pollution?

Answer: Arsenicosis.

Question 24. What is the pollution of water caused due to the algal decomposition called?

Answer: Algal bloom.

Question 25. Name two permanent organic pollutant?

Answer: Dichlorodiphenyltrichloroethane (DDT) and methyl murcury.

Question 26. Which metalloid-compound in responsible for water pollution?

Answer: Arsenic.

Question 27. What is fluorosis disease?

Answer: Fluorosis is a crippling disease resulted from deposition of fluorides in the hard and soft tissues of body caused by excess intake of fluoride through drinking water and affects teeth and bones.

Question 28. Due to the presence of which element itai- itai occurs?

Answer: Due to the presence of cadmium in drinking water itai-itai disease occurs.

Chapter 4 Matter Water Topic C Water Pollutoin Fill In The Blanks

Question 1. The metalloid whose compounds are responsible for water pollution is _________

Answer: Arsenic

Question 2. High _________ power of water makes it more vulnerable towards pollution.

Answer: Solvation

Question 3. Water soluble arsenic compounds like arsenite and arsenate salts are adsorbed by active ________

Answer: Alumina(AI₂O₃)

Question 4. The full form of COD is ________

Answer: Chemical Oxygen Deeman

Question 5. An example of a water-borne disease is _________

Answer: Typhoid

Question 6. Malathion and parathion are ________

Answer: Insecticides

Question 7. _______ is an example of organoarsenic compound.

Answer: Cacodylic acid

Question 8. Continuous lifting of groundwater increases the amount of _______ in water.

Answer: Arsenic

Question 9. ______are used as fillers in detergents.

Answer: Phosphates

Question 10. There are ______ layers of filters in a filtration tank.

Answer: Three

Question 11. The extent of water pollution _______ as the BOD value of water increases.

Answer: Increases

Question 12. The phenomenon of continuous accumulation of toxic chemicals in the fat tissues of living beings is known as ________

Answer: Biomagnification

Question 13. ________ which is a fluoride-containing mineral causes fluoride pollution in water.

Answer: Cryolite

Question 14. DDT, a widely used pesticide is not ________ in nature.

Answer: Biodegradable

Question 15. The amount of dissolved oxygen in water _______ due to eutrophication.

Answer: Decreases

Question 16. Presence of ________ of fluorides in drinking water is favourable for teeth.

Answer: 1 mg • L^-1

Question 17. As a result of eutrophication, the extent of dissolved oxygen in water rapidly ________

Answer: Decreases

Question 18. ________ is used for the removal of arsenic by adsorption method.

Answer: Activated alumina

Chapter 4 Matter Water Topic C Water Pollutoin State Whether True Or False

Question 1. Sulphate salts are responsible for algal bloom in water bodies.

Answer: False

Question 2. Blackfoot disease is caused due to arsenic pollution of water.

Answer: True

Question 3. High value of BOD of a water sample indicates decreased level of water pollution.

Answer: False

Question 4. The two major components of detergent are a surface-active agent and a builder or filler.

Answer: True

Question 5. The element arsenic is directly responsible for arsenic pollution of water.

Answer: False

Question 6. The toxic effects of DDT disrupts the food chain and ultimately causes an imbalance in the ecosystem.

Answer: True

Question 7. Eutrophication can lead to a decrease in the depth of a water body.

Answer: True

Question 8. As COD increases, extent of pollution also increases.

Answer: True

Question 9. Value of COD is generally lower than that of BOD for a sample of water.

Answer: False

Question 10. Malaria is a water-born disease.

Answer: False

Question 11. For prolonged intake of arsenic contaminated water arsenicosis occurs.

Answer: True

Chapter 4 Matter Water Topic C Water Pollutoin Miscellaneous Type Questions

Match the columns

1.

Answer: 1. B, 2. C, 3. D, 4. A

2.

Answer: 1. C, 2. A, 3. D,  4. B