WATER - CLASS 7

CHAPTER - WATER

1.   Water plays a vital role in functioning of all processes in living organisms.

2.   Water is not an element but a Compound.

3.   Water is a compound of elements Hydrogen and Oxygen.

4.   The purest form of water is Rain water.

5.   River and lake water contain soluble salts and impurities.

6.   The most impure form of water is Sea water.

7.   Alum and lime are added to water which coagulate the suspended impurities.

8.   The process in which liquid Chlorine is added to impure water to kill the germs present in the water is Chlorination.

9.   A homogeneous mixture of a solute in a solvent is called a Solution.

10.        Sea water containing over 3% soluble salts including sodium chloride.

11.        Water is a poor conductor of electricity and heat.

12.        Hard water does not lather readily.

13.        The solute must be in a small amount compared to the solvent.

14.        The solute must be in a small amount compared to the solvent.

15.        The mixture of Alcohol and water is an example of miscible mixture.

Ø   Importance of water:

ü  Water plays an important role in all human life processes such as digestion, transportation and excretion.

ü  Plants use water during photosynthesis.

ü  Seeds cannot germinate in the absence of water.

ü  Water also provides an atmosphere for organisms to survive. Aquatic animals and plants and animals use the Oxygen dissolved in water to breath.

ü  Water is essential for coking, bathing, washing, cleaning and in agriculture.

ü  Being a good solvent, Water finds varied application in various industries such as mining, manufacturing beverages, etc.

ü  Rivers and seas serve as mode of transport.

ü  Water is used in the generation of electricity.

Ø   Deep groundwater is normally safe for drinking.

Ø   Ground water will not have any suspended impurities as it gets filtered while passing through different layers of rocks and soils.

Ø   Water is the only substance that exists naturally in all three states.

Ø Heat energy is absorbed when ice changes to water.

Ø Heat energy is evolved when steam changes to water.

Ø   In air water exists as vapour. This vapour in air is referred

d) Answer the followings.

1. State the methods used for the removal of hardness in the water.

Ans:

·         Temporary hardness in water is removed by boiling the water and then filtering it.

·         Permanent hardness in water is removed by adding washing soda (Sodium carbonate) to the water and then filtering it.

2. Give an example of each of the followings

a) Soft water-Rain water      b) Hard water-river, sea and lake water.

3. State the methods used for the obtaining a solute from a solution.

Ans: Evaporation and distillation.

4. Define the followings :

a)   Solubility of a solute :The maximum amount of solute in grams that will dissolve completely in water forming a saturated solution of 100gr

b)   Saturated solution: The solution which cannot dissolve more of the solute in it at a given temperature.

5. Differentiate between Soft water and Hard water.

Hard Water	Soft Water
i.     Hard water does not lather readily with ordinary soaps. ii.    Hard water contains dissolved salts of Calcium and Magnesium. iii.   e.g. Sea water and river water etc.	1.    Soft water lathers readily with ordinary soaps. 2.    Soft water does not contain dissolved salts of Calcium and Magnesium. 3.    e.g. Rain water and distilled water.

6. State the methods of protection of sources of water.

Ans:

·         Pollution of river water must be checked by cleaning rivers on a nationwide basis.

·         Wells should be covered and washing and cleaning should be prevented near the wells.

7. State the effects of water pollution?

Ans: Pollution reduces dissolved Oxygen content in water which affects marine, plant and animal life.

8.    Polluted water acts as a carrier for germs which causes various diseases.

9.    What is potable water? How is water made potable?

Ans: Potable water is the water used for drinking purposes.

The water must be purified in purification plants to make it potable.

10. State the conditions that affect the formation of a solution.

Ans:

·         The solute must be soluble in the solvent.

·         The solute should be in small amount compared to the solvent.

·         The solute must be finely powdered and must not be present as large particles for quicker and complete dissolution of the solute.

·         As the temperature of the solvent increases the solubility of the solute increases.

·         A glass rod should be used for stirring completely the solute and solvent particles.