Question

For the coagulation of 100 mL of $A{s}_2{S}_3$ sol, 5 mL of 1 M NaCl is required. The flocculation value of NaCl is:

• A. $50mmol{L}^{-1}$
• B. $5mmol{L}^{-1}$
• C. $47.6mmol{L}^{-1}$
• D. None of these

Answer 1

The correct option is A $50mmol{L}^{-1}$

Millimoles of NaCl added = 5

Volume of the sol containing NaCl solution = 100 mL.

Flocculation value is the amount of electrolyte (in millimoles) that must be added to 1L of the colloidal solution so as to bring about complete coagulation.

Flocculation value of $NaCl=\frac{5\times 1000}{100}=50mmol{L}^{-1}.$