Question

The coagulation of 200 mL of a positive colloid took place when $0.73\mathrm{g}$ of $\mathrm{HCl}$ was added to it without changing the volume much. The flocculation value of $\mathrm{HCl}$ for the colloid is:

• A. $100\mathrm{m}\mathrm{mol}$
• B. $36.5\mathrm{m}\mathrm{mol}$
• C. $0.365\mathrm{m}\mathrm{mol}$
• D. $150\mathrm{m}\mathrm{mol}$

Answer 1

The correct option is A

$100\mathrm{m}\mathrm{mol}$

Step 1: Given data

1. Volume of Solution= $200\mathrm{ml}$
2. Mass of $\mathrm{HCl}$(given)= $0.73\mathrm{g}$
3. Molar mass of $\mathrm{HCl}$= $36.5\mathrm{g}$

Step 2: Concept of Flocculation and Calculation of Flocculation value

1. Flocculation value is defined as the minimum concentration of an electrolyte required to cause coagulation of Sol.
2. Flocculating value is inversely proportional to the coagulating power of ion.
3. Moles of $\mathrm{HCl}$: $\frac{\mathrm{Given}\mathrm{mass}}{\mathrm{Molar}\mathrm{mass}}$ so, $\frac{0.73}{36.5}=0.02molor20.0mmol$
4. Hence $1\mathrm{L}$ or $1000\mathrm{ml}$ of the solution will require: $\frac{20}{200}\times 1000=100mmol$

Therefore, The flocculation value is $100\mathrm{m}\mathrm{mol}$, so correct option is (A).