Question

A forgetful scientist took three equal samples of water and added 2 ml of soap solution to each of them. He measured the height of the lather formed in each case. His results were 2 cm; 3 cm and 4 cm. Fill in his results correctly in the table given. Which sample was the hardest? Which is the softest? Can you explain the difference in the results between tap water and boiled water?

Water Sample	Height of Lather
distilled water
tap water
boiled tap water

Answer 1

Water Sample	Height of Lather
Distilled water	4 cm
Tap water	2 cm
Boiled tap water	3 cm

Tap water is the hardest and distilled water is the softest.

Difference in results between tap water and boiled tap water:
Tap water contains relatively high amount of calcium and magnesium. This little bit hardness of tap water can be removed by boiling. Hence, when tap water is boiled, the soluble bicarbonates decompose into insoluble carbonates, which can be removed by filtering water through a fine cloth at home. Hence, tap water, due a little hardness, gives little lather, whereas boiled tap water gives comparatively more lather when mixed with soap.