Question

Detergents do not give scum with hard water because they have:
A. Ammonium salts of long chain carboxylic acids.
B. Sulphonate salts of long chain carboxylic acids
C. Both a and b
D. None of the above.

Answer 1

Hint: Let us first understand 2hat is meant by hard water and scum. Hard water is formed when the water percolates through chalk, limestone that are composed of magnesium carbonate, calcium, sulphates and bicarbonate. When soap or other anionic surfactants are added to hard water, they form a substance called scum.

Complete solution:
When the calcium and magnesium ions that are present in hard water react with soap they form an insoluble precipitate called scum. As a result there will be wastage of soap. Detergents are usually ammonium or sulphonated salts of long chains of carboxylic acids. These carboxylic acid chains do not react with the ions of water and hence they do not form an insoluble precipitate scum. Detergents have strong cleansing properly. Detergents form more lather than soap because detergents are more soluble than soaps. Detergents clean more effectively in soft water compared to hard water.

Therefore the correct answer is C. Both a and b.

Note:
In case of hard water, synthetic detergents are used. The main disadvantage of detergents is that there are non biodegradable substances. Excess alkaline components in detergent damages the fabrics.