Question

er) and 10 mL of
test tubes.
Take about 10 mL of distilled water (or rain water) and 10 m
hard water (from a tubewell or hand-pump) in separate test tul
Add a couple of drops of soap solution to both.
Shake the test tubes vigorously for an equal period of time
observe the amount of foam formed.
In which test tube do you get more foam?
In which test tube do you observe a white curdy precipitate?
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Answer 1

thestudent observes that in the test tube where he mixed CaSO₄ with water would give less foam as compared to the other test tube because the water contains salts of Ca which make it hard and normal soaps can't remove it.

In other test-tube there would be much larger foam.