CBSE Class 10 Science 2015 Term II Outside Delhi Set 1

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Question : 19
Total: 36
Both soap and detergent are some type of salts. What is the difference between them? Describe in brief the cleansing action of soap. Why do soaps not form lather in hard water ? List two problems that arise due to the use of detergents instead of soaps.
Solution:  
Soaps are the sodium and potassium salts of long chain carboxylic acids whereas detergents are ammonium or sulphonate salts.
Cleansing action of soap : One part of soap molecules is ionic and dissolves ì water. The other part is non-ionic hydrophobic part which dissolves in oil. Thus soap molecules arrange themselves in the form of a micelle. On rinsing with water soap is washed off lifting the oily dirt particles with it. Soap does not forms lather in hard water because it forms insoluble precipitate.
Problem due to the use of detergent are :
(i) Detergent are non-biodegradable.
(ii) It leads to water or soil pollution.
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