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Temporary Hardness and Removal

Take 10 mL ...

Question

Take $10 m L$ distilled water in a test tube and take the same volume of hard water in another test tube. Add a few drops of soap solution to both the test tubes and shake well. Do both the test tubes contains the same quantity of foam? Which test tube contains more foam? What do you infer?

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Solution

No. Both the test tube does not contains same quantity of foam.

Distilled water taken test tube contains more foam. Soap does not lather well in hard water. The hardness of water is due to dissolved calcium and magnesium salts in it. These salts with soap to form insoluble compounds resulting in the decreases of lather.

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Q. Sunita performs two sets of experiments to study the formation of lather(foam) by using liquid soap.
Set 1 : She takes 10 ml of distilled water in test tube 'A', adds 5-6 drops of liquid soap in it and shakes the test tube vigorously.
Set 2 : She takes 10 ml of distilled water in test tube 'B', adds 5-6 drops of liquid soap in it alongwith half spoonful of CaSO₄, and shakes the test tube vigorously.
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Q. A student takes about 4 ml of distilled water in four test tubes marked

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Q. 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, in 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
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