Distilled Water

Fig: Distillated Process

For ordinary lab use, water is distillated in a copper vessel or stainless steel vessel automatically heated by gas, flame or electricity. A pure sample is obtained by adding a little acidified potassium permanganate solution to ordinary distilled water and allowing the mixture to stand for a few hours. The water is then distilled; the distillate is mixed with a little barium hydroxide and redistilled using a tin condenser.

Advantages of Hard water

1.Hard water is advantageous for the strengthening the bones and teeth.

2.Due to the presence of soluble salts, water becomes tasty otherwise; it is a flap in taste.

3.Hard water is used in beer factory.

Disadvantages of Hard water

1.Large amount of soap is wasted while washing clothes in hard water because it does not produce lather readily.

2.White clothes become dull after regular washing in hard water.

3.When hard water is boiled scales are formed which reduces the life of the boiler.

           

Removal of Permanent Hardness

It is not easy to remove permanent hardness of water as temporary hardness. Permanent hardness can be removed by following methods.

a) Treatment with washing soda: 
       Soluble salts of calcium and magnesium turn into insoluble salts when washing soda (sodium carbonate) is mixed with it.

Fig: Washing soda

CaCl₂ + Na₂CO₃ = CaCO₃ + 2NaCl

MgSO₄ + Na₂CO₃ = MgCO₃ + Na₂SO₄

b) Permutit process: 
        Permutit is the trade name for an artificially prepared sodium zeolite or sodium aluminium orthosilicate obtained by fusing together sodium carbonate, silica and alumina. Its composition corresponds to Na₂Al₂Si₂O₈ or Na₂Z where Z stands for zeolite = Al₂Si₂O₈. It possesses remarkable property of reacting with calcium and magnesium ions forming insoluble calcium or magnesium zeolite. By passing hard water through a cylinder packed with permutit all the ions responsible for the hardness of water are drawn and replaced by sodium ions.

Ca-salt + Na-permutit = Ca-permutit + Na-salt

Mg-salt + Na-permutit  = Mg-permutit + Na-salt

In due course, however, the permutit is exhausted by having given up all its sodium ions. This can be regenerated by soaking in a 10% solution of common salt when the reverse change take place and calcium and magnesium ions pass into solution and sodium zeolite is formed again.

CaZ + 2NaCl = Na₂Z + CaCl₂

MgZ + 2Nacl = Mg₂Z + MgCl₂

Fig: Permutit process

The resulting calcium and magnesium chlorides are washed out and the regenerated permutit used over again.

Removal of Temporary Hardness of Water

As said earlier, temporary hardness of water can be removed easily. The following methods may be adopted for the removal of temporary hardness of water.

i) By boiling:  

Fig: Boiling water

A soluble bicarbonate salt of calcium and magnesium becomes insoluble salt on heating. The insoluble salt settles at the bottom of boiler.

Calcium hydrogen   =  calcium    +     carbon    + water.

            carbonate            carbonate       dioxide

Ca(HCO₃)₂ = CaCO₃ + CO₂ + H₂O

ii) Treatment with lime water : Temporary hardness of water can be removed by treating with lime water. This is known as Clark’s method.

fig: Clark's method of removing hardness of water

Carbonate + lime water = calcium carbonate + water

Ca (HCO₃)₂ + (Ca(OH)₂  = CaCO₃ + 2H₂O