ICSE Class 7 Chemistry Important Questions Chapter 6 Water

Chemistry ICSE Class 7 Important Questions Chapter 6 Water

Question 1.
What is the importance of water ?
Answer:
1. In life process – Water provides medium for all biochemical reaction inside the human body. It acts as carrier of nutrients in body. It regulates the body temperature by sweating and evaporation. Plants need water to prepare food by photosynthesis. Aquatic plants and animals use nutrients and oxygen dissolved in water for their survival.
2. In agriculture – Water is essential for growing crops, germination of seeds, and spraying insecticides and pesticides.
3. In industry – Water is used for generating electricity, in chemical and other industries to prepare medicines, steel, paper, etc.
4. In everyday life – Water is needed for drinking, cooking, washing, bathing, cleaning, etc.

Question 2.
What is the importance of water cycle ?
Answer:
The water cycle helps in controlling the climatic conditions.
It helps in restoring the water lost from the earth’s surface and also helps in maintaining the balance of underground water.

Question 3.
What are the natural sources of water ?
Answer:
Natural sources of water are broadly categorised into surface water and groundwater. Surface water is found in oceans, seas, rivers and lakes. Sources of groundwater include well water and spring water.

Question 4.
What is rainwater ?
Answer:
Water that reaches the earth as rain is called rainwater. It is the primary source of water. It becomes surface water if it reaches water bodies such as the seas, oceans, lakes streams and rivers. If it seeps into the ground and collects above the non-porous rocks, it is called groundwater. It is the purest form of natural water.

Question 5.
Name few impurities present in fresh-water.
Answer:

1. Dissolved impurities – mainly salts of calcium, magnesium, sodium, etc.
2. Suspended impurities – include clay, sand, leaves, straw, etc.
3. Microorganisms – like bacteria which cause waterborne diseases.
4. Dissolved gases – like carbon dioxide, sulphur dioxide and nitrogen dioxide are added by rainwater.

Question 6.
Name the steps followed for purification of natural water in cities before it is supplied to our homes.
Answer:
Removal of suspended impurities through sedimentation, loading and Alteration.
Destroying harmful microorganisms through chlorination
Storage

Question 7.
What is distillation ?
Answer:
The process of converting a liquid into its vapour by heating and then condensing the vapour back into the liquid is called distillation. This method is used to remove dissolved impurities, from water. It is the purest form of water and also called chemically pure water.

Question 8.
What is freezing mixture ?
Answer:
When common salt is added to ice, its melting point (freezing point of water) gets lowered. Such a mixture is called a freezing mixture. The melting point of the freezing mixture is about-15°C. ,

Question 9.
What are miscible and immiscible liquids ?
Answer:
1. Liquids like alcohol and vinegar that dissolve in water are called miscible liquids.
2. Liquids like petrol and vegetable oil that do not dissolve in water are called immiscible liquids.

Question 10.
Mention few physical properties of water.
Answer:

1. It is a colourless, odourless and tasteless liquid.
2. its boiling point is 100°C
3. Its freezing-point is 0°C
4. Pure water is a bad conductor of heat and electricity.
5. Its density is lg/cm³ at 4°C

Question 11.
What is hard water and soft water ?
Answer:
Water that easily forms rich lather (soap bubbles) with soap is called soft water. Examples : Rainwater and distilled water.
Water that does not form lather easily with soap is called hard water.

Question 12.
What causes hardness of water ?
Answer:
Hardness of water is caused by dissolved salts of calcium and magnesium such as bicarbonates, carbonates and chlorides.

Question 13.
Differentiate between temporary and permanent hardness of water.
Answer:
Temporary hardness :

1. It is due to the dissolved bicarbonates of calcium and magnesium.
2. It can be removed by boiling.

Permanent hardness :

1. It is due to the dissolved chlorides and sulphates of calcium and magnesium.
2. It cannot be removed by boiling but by adding washing soda.

Question 14.
Name few water pollutants.
Answer:
Domestic waste (sewage), industrial waste, chemicals like fertilizers, pesticides; oil, etc.

Question 15.
What are water – borne diseases ? Name few. How can they be avoided ?
Answer:
Diseases caused by consuming contaminated water are called water borne diseases. Some of waterborne diseases are cholera, typhoid, dysentery, hepatitis A (jaundice). Steps to avoid water borne diseases.

1. The main steps for reducing the spread of waterborne diseases is to use clean and treated water for drinking and preparing food.
2. Proper disinfection of water to kill and prevent the growth of disease-causing microorganisms is necessary.
3. People should maintain personal hygiene and cleanliness.
4. Proper waste disposal should be ensured.

Question 16.
Fill in the blanks.
1. The chemical frame of water is ………….
Answer:
The chemical name of water is dihydrogen monoxide.

2. The human body contains about ………… water.
Answer:
The human body contains about 70% water.

3. …………. is formed as a by product of respiration in humans and burning of fossil fuels.
Answer:
Water vapour is formed as a by product of respiration in humans and burning of fossil fuels.

4. …………. and …………. are the largest source of natural water.
Answer:
Oceans and seas are the largest source of natural water.

5. The sources of water in rivers and lakes are ………….. and ………….
Answer:
The sources of water in rivers and lakes are rainfall and glaciers. water is the purest form of water obtained.

6. ……….. is the primary source of water.
Answer:
Rainwater is the primary source of water.

7. ……….. ¡s the purest form of natural water while …………. is the purest form of water obtained.
Answer:
Rainwater is the purest form of natural water while distilled water is the purest form of water obtained.

8. The freezing point of water ………… with increase in pressure.
Answer:
The freezing point of water decreases with increase in pressure.

9. Water is ………….. to litmus.
Answer:
Water is neutral to litmus.

10. Water reacts with metals to form ………… gas and metal hydroxides.
Answer:
Water reacts with metals to form hydrogen gas and metal hydroxides.

11. Water reacts with non-metal oxides to form …………..
Answer:
Water reacts with non-metal oxides to form acids.

12. Minamata disease in Japan was caused by high levels of ………… in fish
Answer:
Minamata disease in Japan was caused by high levels of mercury in fish ,

13. About …………… of the earth’s surface is covered with water.
Answer:
About 71% of the earth’s surface is covered with water.

14. Water ………….. on cooling below 4°C.
Answer:
Water expands on cooling below 4°C.

Question 17.
Write the products formed when water reacts with :
active metals
metal oxides
non-metal oxides
Answer:
(i) Forms metal hydroxide and hydrogen gas. Example :
2K + 2H₂O → 2KOH + H₂
Forms metal hydroxide. Example :
Na₂O + H₂O → 2NaOH
Forms acids. Example :
CO₂ + H₂O →H₂CO₃

Concept Map :

Concept Map:

ICSE Class 7 Chemistry Important Questions