Living Science Chemistry Class 6 ICSE Solutions Chapter 7 Water

ICSE Living Science Chemistry for Class 6 Solutions Chapter 7 Water

Check Your Progress

Answer these questions.
Question 1.
Name the purest form of natural water.
Answer:
Rainwater

Question 2.
Why is sea water unfit for drinking and irrigation.
Answer:
Sea water contains a large amount of dissolved salts and therefore, cannot be used for drinking or irrigation directly.

Question 3.
In which form is water present in the atmosphere ?
Answer:
Gasesous form (water vapour)

Question 4.
What is the continuous circulation of water in nature called ?
Answer:
Water cycle

Check Your Progress

Answer these questions.
Question 1.
What is potable water ?
Answer:
Water that is fit for drinking is called potable water.

Question 2.
Name two chemicals added to water to destroy germs present in it.
Answer:
Bleaching powder or chlorine tablet and potassium permanganate.

Question 3.
Why is water called the universal solvent ?
Answer:
Water is called the universal solvent because it dissolves a large number of substances to form solutions.

Question 4.
How will you know whether a given solution is saturated or unsaturated ?
Answer:
It more solute can dissolve in the solution at a given temperature, it is unsaturated solution. If more solute cannot dissolve in the solution at a given temperature, it is saturated solutioa

A. Tick the most appropriate answer.

Question 1.
The purest form of natural water is –
a. rainwater
b. sea water
c. well water
d. river water
Answer:
a. rainwater

Question 2.
A method used to kill germs in water is –
a. filtration
b. sedimentation
c. loading
d. boiling
Answer:
d. boiling

Question 3.
To kill germs in water, some modem filters make use of –
a. infrared rays
b. X-rays
c. ultraviolet rays
d. none of these
Answer:
c. ultraviolet rays

Question 4.
Which of the following is not a waterborne disease ?
a. Diarrhoea
b. Dysentery
c. Typhoid
d. Bronchitis
Answer:
d. Bronchitis

Question 5.
A factor which can affect the formation of a solution is –
a. colour of the solute
b. size of solute particles
c. taste of the solute
d. all of these
Answer:
b. size of solute particles

Question 6.
The solubility of most solutes in water increases with –
a. force
b. time
c. temperature
d. none of these
Answer:
c. temperature

B. Fill in the blanks.

Question 1.
In the gaseous state, water is present as …………… in the atmosphere.
Answer:
In the gaseous state, water is present as water vapour in the atmosphere.

Question 2.
The water that is fit for drinking is called ………….. water.
Answer:
The water that is fit for drinking is called potable water.

Question 3.
………….. is a chemical added in the process of loading.
Answer:
Potash alum is a chemical added in the process of loading.

Question 4.
A ………….. is a homogeneous mixture of a solute in a solvent.
Answer:
A solution is a homogeneous mixture of a solute in a solvent.

Question 5.
A …………… solution dissolves no more solute at a particular temperature.
Answer:
A saturated solution dissolves no more solute at a particular temperature.

Question 6.
The process of collecting and storing rainwater for future use is called
Answer:
The process of collecting and storing rainwater for future use is called rainwater harvesting.

C. Match the following

Column A	Column B
1. Evaporation	a. process by which pure water is obtained
2. Diarrhoea	b. water cycle
3. Sca water	c. suspended impurities in water
4. Distillation	d. large amounts of dissolved salts
5. Charcoal	e. waterborne disease
	f. groundwater

Answer:

Column A	Column B
1. Evaporation	b. water cycle
2. Diarrhoea	e. waterborne disease
3. Sca water	d. large amounts of dissolved salts
4. Distillation	a. process by which pure water is obtained
5. Charcoal	c. suspended impurities in water

D. State if the following statements are true or false. Correct the statement if it is false.

Question 1.
Underground water can be used by digging wells and tube wells.
Answer:
True

Question 2.
Rainwater contains large amounts of dissolved salts.
Answer:
False. Sea water contains large amounts of dissolved salts.

Question 3.
For sterilizing water, charcoal is used.
Answer:
False. For sterilizing water, chlorine is used.

Question 4.
Reverse osmosis is used to remove suspended impurities.
Answer:
False. Reverse osmosis is used to remove dissolved impurities.

Question 5.
Stirring causes the solute to dissolve faster in a solution.
Answer:
True

Question 6.
Distilled water is good for drinking purposes.
Answer:
False. Distilled water is not good for drinking purposes.

Question 7.
Acid rain harms aquatic life.
Answer:
True

E. Define the following terms.
1. Water cycle
2. Transpiration
3. Potable water
4. Saturated solution
5. Solubility
Answer:
1. Water cycle – The continuous circulation of water from the earth to the atmosphere and back to the earth is called as the water cycle.
2. Transpiration – Transpiration is the process by which plants lose water in the form of water vapour to the atmosphere through leaves.
3. Potable water – Water that is fit for drinking is called potable water.
4. Saturated solution – A saturated solution is a solution in which no more solute can dissolve at a given temperature.
5. Solubility – The quantity of a solute that dissolves in a given quantity of a solvent at a specific temperature is called the solubility of the solute. It is expressed in terms of grams of solute per 100 g of solvent.

F. Answer the following in short.

Question 1.
What is surface water ?
Answer:
Surface water is any source of water that flows or is stored on the surface of the earth. It includes rainwater and the water in rivers, lakes, seas and oceans.

Question 2.
What is underground water ?
Answer:
Rainwater and the water from the water bodies that seep through the soil and collects over the non-porous rocks inside the earth is called underground water or ground water.

Question 3.
State two sources of a. surface water b. underground water.
Answer:
(a) Rainwater, river, lake, sea, ocean.
(b) Rainwater and water bodies like rivers, streams, etc.

Question 4.
Why is rainwater considered the purest form of natural water ?
Answer:
Rainwater is the purest form of natural water since it is formed by condensation of water vapour.

Question 5.
Why is bleaching powder added to water in the waterworks ?
Answer:
Bleaching powder releases chlorine which dissolves in water and kills germs. Hence, it is used to purify water by destroying germs present in it.

Question 6.
Name any two methods used at home to make water fit for drinking.
Answer:
Boiling, Filteration

Question 7.
List three major causes of water pollution.
Answer:

1. Domestic sewage like faeces, sewage, etc.
2. Industrial waste
3. Insecticides and pesticides
4. Oil spillage

Question 8.
What is the conservation of water ?
Answer:
Conservation of water refers to preventing the wastage of water without affecting day-to-day life.

G. Answer the following in detail.

Question 1.
State the three states of water. How is the inter-changeability of the three states of water achieved ?
Answer:
The three states of water are :

1. Solid – as ice, snow, frost, mist, etc.
2. Liquid – in oceans, seas, rivers, lakes, springs, rainwater etc.
3. Gas – as water vapour in the atmosphere

Water can be changed from one form to another, i.e., solid to liquid to gaseous state by changing the temperature. On heating, ice (solid state) melts and changes to water (liquid state). On cooling, water changes to ice. On heating, water (liquid state) boils and changes into steam (gaseous state). On cooling, steam condenses and changes back to water. Thus, the three states of water can be changed from one form to another by changing the temperature.

Question 2.
Explain the water cycle with the help of a diagram. Also write the importance of the water cycle.
Answer:

The water cycle involves evaporation (and transpiration), condensation, precipitation and collection.
1. Evaporation and transpiration – Sun heats up water in rivers, lakes, seas, etc. into water vapour. Plants also add water vapour to the atmosphere through their leaves by transpiration.
2. Condensation – Water vapours being lighter rise up and condense to form water droplets (by the cool air up in the atmosphere). These droplets collect together to form clouds.
3. Precipitation – It occurs when tiny droplets in the clouds combine to form large droplets, become heavy and fall down as rain, snow, hail or sleet on the earth.
4. Collection – On the earth, water flows across land and reaches river, lake, stream, sea and also seeps through soil to form groundwater. The water from water bodies evaporate again and water cycle continues in nature.

Importance of the water cycle :

1. The water cycle helps in controlling the climatic conditions.
2. It helps in restoring the water lost from the earth’s surface and maintaining the balance of water on the earth.
3. Cultivation of crops depends mostly on rainwater.

Question 3.
State the important uses of water in our daily life.
Answer:
Importance of water in daily life :

1. Water is needed for drinking, washing, cooking, bathing, cleaning, etc.
2. It is used to generate electricity in hydroelectric power stations.
3. It is used for irrigating fields and in the manufacture of various products like medicines.
4. Water serves as a means of transportation of goods and people.
5. It is used to extinguish fires.

Question 4.
Explain the methods used for removal of a. suspended impurities b. germs from water.
Answer:
(a) Methods used to remove suspended impurities are :

1. Sedimentation : Water from sources like river or lakes is first fed into a sedimentation tank. After some time, most of the suspended impurities settle down under the effect of gravity and water becomes clear.
2. Loading : It increases the rate of sedimentation by adding chemicals like potash alum. This makes the fine, suspended particles heavier and they settle down at the bottom of the loading tank.
3. Filtration : The water is passed through a filtration tank, which contains layers of fine sand, gravel and charcoal. These layers act as filters. After passing through these, water is absolutely free from suspended impurities.

(b) Removal of germs from water is done by chlorination. The filtered water is sterilized by adding bleaching powder or by passing chlorine gas. Bleaching powder releases chlorine which dissolves in water and kills germs.

Question 5.
Differentiate between saturated and unsaturated solutions.
Answer:
A saturated solution is a solution in which no more solute can dissolve at a given temperature. A saturated solution becomes unsaturated on heating. An unsaturated solution is a solution in which more of the solute can be dissolved at a given temperature. An unsaturated solution becomes saturated on cooling.

Question 6.
List five ways to reduce water pollution.
Answer:
Ways to reduce water pollution :
1. Effluent treatment – The chemical wastes released from industries should be treated in effluent treatment plants to remove harmful chemicals present in them before discharging into water bodies like river, lake, etc.
2. Sewage treatment – Sewage should be treated in sewage treatment plants before being released into rivers.
3. Recycling of industrial wastes – Waste products from factories should be recycled and used before being released.
4. Organic farming – Excessive use of insecticides and pesticides should be reduced and organic fanning should be encouraged.
5. Biodegradable detergents – The use of synthetic detergents should be reduced and more of biodegradable detergents should be used.

H. Give reasons for the following.

Question 1.
Boiling is the most recommended water purification technique at home.
Answer:
Boiling is the easiest and cheapest method of water purification at home. It kills germs and feasible at home.

Question 2.
Water is called the universal solvent.
Answer:
Water is called the universal solvent as it dissolves a large number of substances in it to form solutions.

Living Science Chemistry Class 6 ICSE Solutions