Question

In an experiment, addition of $4.0mL$ of $0.005MBaC{l}_2$ to $16.0mL$ of arsenious sulphide sol just causes complete coagulation in $2h$. The flocculating value of the effective ion is:

• A. $B{a}^{2+},1.0$
• B. $B{a}^{2+},2.0$
• C. $C{l}^{-},1.0$
• D. $C{l}^{-},2.0$

Answer 1

The correct option is A $B{a}^{2+},1.0$

The flocculating value of the effective ion ($B{a}^{2+}$) is 1.0.
The flocculating value is the minimum amount of an electrolyte required to cause precipitation of one liter of colloidal solution.

Volume of barium chloride required to cause precipitation of one liter of colloidal solution
$=\frac{4.0}{16+4}\times 1000=200$ mL

Number of millimoles of barium chloride $=200\times 0.005=1$ mmol