Page 239 - Chemistry ICSE Class IX

Chemistry Practicals 227

VIVA VOCE

1. Name the salts which cause hardness in water.
Ans. Hardness in water is caused by the presence of the following salts in water:
™ Temporary hardness is caused by
y Calcium hydrogencarbonate
y Magnesium hydrogencarbonate
™ Permanent hardness is caused by
y Calcium chloride
y Magnesium chloride
y Calcium sulphate
y Magnesium sulphate
2. What are soaps?
Ans. Sodium or potassium salts of higher fatty acids are called soaps.
3. Name a higher fatty acid.
Ans. Oleic acid (C H COOH), Stearic acid (C H COOH).
17 33 17 35
4. Why do soaps not produce lather when used in hard water?
Ans. The calcium/magnesium salts present in hard water react with soap forming insoluble, curdy precipitate. That is why,
soaps do not give lather (foam) with hard water.
5. Name the reagent used to differentiate between temporary and permanent hard water.
Ans. Soap solution.
6. Which hardness of water can be removed by heating?
Ans. Temporary hardness of water is removed by heating/boiling.
7. Name the reagent that can remove both temporary and permanent hardness of water.
Ans. Washing soda, (Na CO )
2 3
8. What are the advantages of using detergent over soap in hard water?
Ans. Advantages of using detergent over soap in hard water:
y Detergents function very well in hard water, whereas soaps do not.
y Detergent solution gives lather with hard water, whereas soap solution does not.
y They are more soluble than soaps, in water.
y They can be used in an acidic medium.
y They have a stronger cleansing action as compared to soaps.
y They are prepared from hydrocarbons of petroleum and do not require expensive vegetable oils for their preparation.