Question

For coagulation of $250mL$ of $Fe(OH{)}_3$ sol, $2mL$ of $1MN{a}_{2}S{O}_4$ electrolyte is required. What is the coagulating value of $N{a}_{2}S{O}_4$ electrolyte?

Answer 1

Coagulation value is the minimum concentration of electrolyte in millimoles required to cause coagulation of one litre of colloidal solution.

Here, $250mL$ of $Fe(OH{)}_3$ sol is coagulated by $2mL$ of $1MN{a}_{2}S{O}_4$ electrolyte

For 250 mL $\to 2mLof1MN{a}_{2}S{O}_4$
$Noofmillimoles=2\times 1$
$Noofmillimoles=2$
$\therefore$ 2 millimoles for 250 mL
For 1000 mL (1L) $=4\times 2=8mmol$
$\therefore$ Coagulation Value = 8