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Question
Answer the following question.
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 Answer 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.
Solution
Test tube A contains distilled water which is considered as soft water, free from ions like Mg2÷, Ca2+, etc. So, in this case, the length of foam will be the longest(maximum). Test tube B contains underground water which contains ions like Mg2+, Ca2÷, etc. which react with soaps to form salts of fatty acids called scum, which is insoluble in water. So, in this case, the length of foam will be less in comparison to test tube A. Test tube C contains distilled water with CaSO4, which contains Ca2÷ ions which react with soaps to form salts of fatty acids called scum, which is insoluble in water. So, in this case, also, the length of foam will be less in comparison to test tube A.
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