(a) Explain the process of preparation of soap in laboratory.
(b) Why is common salt (sodium chloride) added during the preparation of soap ?
(c) Why is soap not suitable for washing clothes when the water is hard ?
Lakhmir Singh Chemistry Class 10
Answers
a. Soap is made in the laboratory by the process of Saponification. The process involves reacting a vegetable oil, like palm oil, or olive oil with alkali, like Sodium Hydroxide. The reaction is exothermic in nature, liberating heat during the reaction. The final white suspension thatare the products of the reaction, contain soap and glycerol.
b. When we add salt which is sodium chloride, it gets ionised in water and the sodium ions causes the sodium ions of soap to combine with the fatty acid ions and separate as solid soap. This helps in complete removal of soap from the reaction mixture.
c.Hard water contains bicarbonates, chlorides, and sulphates of calcium and magnesium which react with soap molecules forming insoluble precipitates called 'scum'. Hence, strenght of soap molecules are lost in the chemical reaction and they are not available for cleansing action.