Question

What are detergents chemically? List two merits and demerits of using detergents for cleansing. State the reason for the suitability of detergents for washing, even in the case of water having calcium and magnesium ions.

Answer 1

Hint: Detergents are associated colloids and they help in cleansing by forming micelles. They have a lyophilic i.e. water loving group at one end and a lyophobic i.e. oil loving group at the other end.

Complete step by step solution:
Detergents are chemically defined as “ammonium or alkyl benzene sulphonate salts of a long chain of carboxylic acids.
They are a family of compounds which are water soluble cleansing agents similar to soap. They combine with impurities and dirt to make them more soluble. Examples of detergent are:
Two merits of using detergents for cleansing are as follows:
As compared to soap, detergents are more effective for the purpose of cleaning oil and dirt.
They can be used for cleaning even if the water is hard and unlike soap, they do not form lather with hard water.
Two demerits of using detergents for cleansing are as follows:
They are non-biodegradable and cause water and soil pollution.
They are highly basic and harmful to skin.
Now we will look the reasons for suitability of detergents, even in case of water having calcium and magnesium ions which are as follows:
Due to the presence of bicarbonates, chlorides and sulphates of calcium and magnesium, water becomes hard and when sufficient amounts of soap is added they produce lather and stick with clothes.
But when detergent is added to hard water, they form calcium and magnesium salts of detergents which are soluble in water and therefore no lather is formed.
Therefore, we can conclude that detergents can be used even with hard water.

Note: It should be remembered that detergents can also be used in acidic medium as they are salts of strong acids and do not decompose in acidic medium.