Question

Describe hardness in water and its effect on water quality with you own words. (2 pages)

Answer 1

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Water can be divided into two broad categories based on the properties.

1. Soft water and 2. hard water

1. Soft water: The water which forms lather easily with soap is called soft water. Examples are distilled water and rain water.

2. Hard water: The water which does not form lather easily with soap but forms a white curdy precipitate is called hard water. Examples are sea water and well water. This water contains mainly soluble salts as bicarbonates, chlorides and sulfates of magnesium and calcium.

Action of soap: Soap is the sodium or potassium salts of higher fatty acids like staeric acid, palmitic acid or oleic acid. If soap is added to soft water, it is dissolved and lather is formed. If soap is added to hard water, a curdy white precipitate is formed due to the formation of calcium and magnesium salts as cacium stearate and magnesium stearate..

Hardness is further divided into two categories 1. Temporary hardness and 2. Permanent hardness.

1. Temporary hardness: This is due to the presence of bicarbonates of calcium and magnesium. It is called temporary hardness because this can be removed by just boiling the water.

2.Permanent hardness: This is due to the chlorides and sulfates of calcium and magnesium. This cannot be removed by normal boiling method. This requires chemical treatment such as 1. Permutit process or zeolite process 2. ion-exchange process.

Disadvantages of hard water (effect on water quality):

The dissolved salts cause undesirable effects when hard water is used for various purposes.

1. Domestic use:

(a) Washing & bathing: Hard water does not form lather easily with soap as a result, a large amount of soap is wasted.

(b) Cooking: The boiling point of water is increased due to the presence of salts, hence more fuel is consumed for cooking.

(c) drinking: Hard water causes bad effects on digestive sysytem, sometimes stone formation in either kidney or gall bladder.

2. Industrial use:

(a) textile industry; hard water causes wastage of soap, precipitates of calcium and magnesium adhere to the fabrics and cause problem.

(b) paper industry: calcium, magnesium and iron salts in water may effect the quality of paper.

(c) sugar industry; water containing salts of sulfates, carbonates, nitrates effect the crystallization of sugar

(d) dyeing industry: Salts of calcium and magnesium in hard water react with dyes and spoil the desired shade.

3. Boilers:

(a) scale formation: when hard water is boiled, the bicarbonates of calcium and magnesium are decomposed into insoluble carbonates and get deposited on the inner waals of boiler in the form of scales. These act as heat insulators and cause wastage of fuel

(b) Danger of explosion; When the scale cracks, water comes in contact with red hot iron plates. This causes formation of a large amount of stean suddenly. Sometimes, evolution of hydrogen gas also increases the pressure enormously. Thus, it leads to boiler explosion.

(c) corrosion: the presence of CaCl2 and MgCl2 will cause corrosion of iron because these salts on hydrolysis produce HCl. This leads to spoiling of the boiler metal.

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