Question

Riya performs two set of experiments to study the length of the foam formed which follows
Set $I$: She takes $10ml$ of distilled water in test tube ${}^{\prime \prime }{A}^{\prime \prime }$ and adds $5-6$ drops of liquid soap in it and shakes the test tube vigorously.
Set $II$: She takes $10ml$ of distilled water in a test tube ${}^{\prime \prime }{A}^{\prime \prime }$ and adds $5-6$ drops of liquid soap with half spoonful of $CaSO4$ in it and shakes the tube. Write your observation and reason.

Answer 1

While performing both experiments, foam will be formed.

In Set I we will have more length of foam because it consist of soft water. It's because,

In Set II we will have less foam because it consist of hard water due to the presence of CaSO4. The addition of Calcium salt makes the distilled water hard and leads to the formation of scum. Soaps don't react efficiently in hard water.