SS1 Chemistry Lesson Note on Water: Uses; Characteristics; Water Pollutants and Types of Water

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TOPIC:          WATER

CONTENTS:

1. SOURCE OF WATER
2. TYPES OF WATER (SOFT AND HARD)
3. WATER POLLUTANTS
4. USES OF WATER AND LABORATORY PREPARATION OF WATER

WATER

“Water is Life”. It is the most important and the most abundant on earth. It is of great importance to all plants and animals. The human body is over 6o percent water and it is present in equally the same amount in plants. It should however be noted that water is not available everywhere and its availability at certain parts of the world has led to the influx of man to those areas to set up villages and towns.

PERIOD 1:   SOURCE OF WATER: Water can either be found as a natural source or as treated water. There are many sources of water found on the earth’s surface, they include rain water, spring water, well-water, river water, lake water and sea-water. Rain water is the purest form of natural water because it is formed as a result condensation of water in the atmosphere. Spring water contains a considerable amount of mineral salt; but very little suspended impurities such as dust and bacteria. Well-water contains a lot or clay and other mineral salts. Deep well-water tends to be less polluted than surface well-water. River water, Lake water and Sea-water contain a lot of dissolved air, mineral salts, bacteria and organic remains.

All these waters have to be purified before they can be used for drinking. And all the type of natural water are in constant circulation, forming a gigantic water cycle.

TREATED WATER

Treated water are usually prepared for special purposes. Examples are distilled water, pipe-borne water for townships and chlorinated water used in swimming pool.

DISTILLED WATER

Distilled water is chemically pure water prepared by condensing steam using Lie big condenser. If ion exchange resin is used in preparing the water, it is called ionized water.

EVALUATION

1. (a) List four sources of water. (b) Which of the listed source of water in (a) is the purest? Give reason.
2. Explain the how distilled water is obtained.

PERIOD 2: TYPES OF WATER (SOFT AND HARD)

Water is of two types namely: Soft water and Hard water.

1. Soft water: Water is said to be soft if it readily forms lather with soap. Examples are rain water, tap water.
2. Hard water: Hard water is water which will not form lather with soap. Examples are river water, lake water, stream water and sea water.

Types of hard water

There are two types of hard water namely:

1. Temporary hard water: This the hardness caused by the presence of dissolved Ca(HCO₃) and MgCO₃ in water and can be removed by boiling.
2. Permanent hardness: This is the hardness caused by the presence of CaSO₄, MgSO₄ and chlorides which cannot be removed by boiling but by addition of washing soda, caustic soda and ion exchange method.

Advantages of hard water

1. It has pleasant taste than soft water and tasteless water.
2. It does not dissolve lead pipes of pots unlike soft water which dissolves led pipes.
3. It is good for healthy teeth and bones because it contains calcium which is an important element in formation of teeth and bones of animals.
4. Animals like snail and crabs are able to make their shell with the help of hard water.

Disadvantages of hard water

1. It causes furring of kettle and boilers unlike soft water.
2. It infers with processes used to dye materials and tan hides.
3. It forms scum with soap thus, wasting soap unlike soft water.

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