Q27 of 56 Page 1

A student takes about 4 mL of distilled water in four test tubes marked P, Q R and S.

He then dissolves in each test tube an equal amount of one salt in one test tube, namely sodium sulphate in P, potassium sulphate in Q calcium sulphate in R and magnesium sulphate in S. After that he adds an equal amount of soap solution in each test tube. On shaking each of these test tubes well, he observes a good amount of lather (foam) in the test tubes marked

The hard water contains calcium (Ca2+) and magnesium ions (Mg2+). So, the salts which can made the water hard are Magnesium sulphate, Calcium sulphate and calcium chloride. Therefore, preventing soap, to form lather whereas in sodium sulphate and potassium sulphate, soap can form good amount of lather in the test tube.

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