‘A’ is a protecting colloid. The following data is obtained for preventing the coagulation of 10 mL of gold sol to which 1 mL of 10% NaCl is added. What is the gold number of ‘A’?
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The gold number is a measure of the protective power of a colloid. The lower the gold number, the greater the protective power of the colloid.
The gold number is defined as the amount (in mg) of a protecting colloid required to prevent the coagulation of 10 mL of a gold sol when 1 mL of 10% NaCl is added.
From the given data:
In the first experiment, 40 mg of A prevents coagulation.
In the second experiment, 35 mg of A prevents coagulation.
In the third experiment, 25 mg of A does not prevent coagulation.
In the fourth experiment, 32 mg of A does not prevent coagulation.
In the fifth experiment, 33 mg of A prevents coagulation.
The gold number is the amount of A required to just prevent coagulation.
Conclusion:
The correct amount for coagulation prevention is 33 mg. Thus, the gold number of ‘A’ is \( \mathbf{33} \).
