Q23 of 27 Page 1

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.

The length of the foam (lather) will be the longest in test tube A, which contains only distilled water. This is because lather forms easily in soft water. Distilled water is soft water i.e. it doesn’t contain any salts and hence lather will form easily in test tube A.

Tube B and C contain dissolved salts making them hard waters. They react with soap solution and form scum because of the calcium and magnesium salts with little lather.


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