Question

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.
(a) In which test tube, A or B, less lather is formed? Why?
​(b) In which test tube, A or B, more lather is formed? Why?

Answer 1

Presence of $CaSO_4$makes it hard

Explanation:

Set I will have more length of foam because it consists of soft water.

Set II will form less foam because it consists of hard water due to the presence of $CaSO_4$.

In the set, I large amount of foam will be produced as water is soft. But in set Il very less amount of foam will be produced as calcium sulphate is added to the water so the water becomes hard.