Question

When ${6\times 10}^{-5}$ g of a protective colloid was added to a 20ml of standard gold sol, the precipitation of latter was just prevented on addition of 2ml of 10%NaCl solution. The gold number of protective colloid is?

• A. 3
• B. ${3\times 10}^{-5}$
• C. 0.06
• D. 0.03

Answer 1

The correct option is D 0.03

solution:

Gold number of colloid = 0.00003×1000 milligrams

=0.03

In the given problem, to prevent the coagulation of 20 ml of standard gold sol by the rapid addition of 2 ml of 10% NaCl solution, we added 0.00006 grams of colloid. Therefore, to prevent the coagulation of 10 ml of standard gold sol by the rapid addition of 1 ml of 10% NaCl solution, we would need 0.00003 grams of colloid.

hence the correct option:D