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Classification of Colloids - Based on nature of interaction

When 6 × 10...

Question

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

A

3

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B

3 \times 10^{- 5}

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C

0.06

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D

0.03

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Solution

The correct option is D $0.03$
In the given problem, to prevent the coagulation of 20 ml of standard gold sol by the rapid addition of 2 ml of 10% $N a C l$ 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.

Gold number of colloid = $0.00003 \times 1000$ milligrams
= $0.03$

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