Question

On the addition of 1 mL of 10% NaCl to 10 mL of gold sol in the presence of 0.0250 g of starch, the coagulation is just prevented. Starch has the gold number:

Options

• 0.025

• 0.25

• 2.5

• 25

Answer 1

25

Explanation:

The gold number is the minimum amount of a protective colloid (in mg) that prevents the coagulation of 10 mL of gold sol by 1 mL of 10% NaCl. Here, 0.0250 g (25 mg) of starch just prevents coagulation, so the gold number of starch is 25.

This means starch has a gold number of 25, indicating the amount needed to stabilize gold sol against coagulation.