Question

Explain why -

(i) Oil does not mix in water. However, oil and water become homogeneous if a sufficient quantity of detergent is added.

(ii) Soap cannot be used in hard water.

Answer 1

(i)

• A molecule of a detergent holds on to a water molecule at one end and an oil molecule at the other.
• As a result the molecules of oil mix with the water, and we will see that the water and oil have become homogenous and the colour of the mixture appears milky.

(ii)

• Soaps can not be used in hard water because they lose their cleansing property when used with it. Soaps do not form lather with hard water and instead forms scum, as a result of which it loses their cleansing property.