In three test tubes a, b, and c, three different liquids namely distilled water, underground water and distilled water in which a pinch of calcium sulphate is dissolved, respectively are taken. Equal amount of soap solution is added to each test tube and the contents are shaken. In which test tube will the length of the foam (lather) be longest ? Justify your answer
Answers
Answer:
Test tube 'a' will form longest lather.
Explanation:
This can be explained on the basis of hardness of water. Hard water means the water which contains high amount of mineral salts. Minerals salt are salts of calcium, magnesium, sodium. There are two types of hardness.
Permanent hardness which is caused by sulphate,nitrates and chloride salt of Calcium and magnesium.
Temporary hardness is caused by Carbonate and bicarbonate salt of calcium magnesium
Soap are actually sodium salt of long fatty acid.
When soap is dissolved in hard water the sodium get displaced by calcium and magnesium which forms a insoluble salt called 'scum'.
Thus foam is not formed in sufficient amount.
in distilled water there are ideally no electrolytes. So soap will dissolve completely and form maximum foam or lather.
In ground water or test tube 'c' due to salts , scum will be formed causing decrease in foam amount.