Question

In order to cause coagulation of $100\text{mL}$ arsenous sulphide sol $11.2\text{mL}$ of $2MNaCl$ solution is used. What will be the flocculation value of $NaCl$?

Answer 1

The minimum amount of an electrolyte required to cause precipitation of one litre of colloidal solution is called coagulation value or focculation value for the sol.

$11.2\text{mL}$ of $2MNaCl$ contain = $11.2\times 2=22.4\text{mmol}$
$100\text{mL}$ of sol require $22.4\text{mmol}$ $NaCl$ So,
millimole of $NaCl$ require for 1 litre solution
$=\frac{2\times 11.2\times 1000}{100}=224\text{mmol}$