Question

The protecting power of lyophilic colloidal sol is expressed in terms of

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Answer 1

The protecting power of lyophilic colloidal sol is expressed in terms of gold number:
Gold number is the minimum amount of protective colloid in milligrams which when added to $10mL$ of a standard gold sol just sufficient to prevent a colour change from red to blue on the addition of $1mL$ of 10% $NaCl$ solution.

$\text{Gold number}=\frac{\text{Weight of lyophilic sol in mg}\times 10}{\text{Volume of gold sol in mL}}$

$\text{Protective power}\propto \frac{1}{\text{Gold number}}$