Rani got a cut on her finger while working in the kitchen. She applied an antiseptic liquid to stop bleeding but it was not effective. Her husband asked her to rub alum on the cut. To her surprise, the bleeding stopped.

(a) Why was the antiseptic liquid not effective ?

(b) What was the use of alum here ?

(c) Who according to you has a proper knowledge of colloidal solutions - Rani or her husband ?

(a) The antiseptic liquid was not effective because antiseptics are mainly used to kill or prevent the growth of microorganisms, not to stop bleeding. They do not have properties that help in clotting blood.

(b) Blood consists of haemoglobin, which are charged colloidal particles. Alum dissolves in water to provide ions. As they come in contact with blood, they neutralize the charge on the colloidal particles. The blood becomes thick and bleeding stops.

(c) Rani’s husband has a better understanding in this situation.
He knew that if alum is rubbed on the cut, blood stops flowing as alum neutralizes the charge on the colloidal particles of haemoglobin.