Question

Which of the following statements about colloids is False?

• A. Colloidal particles can pass through ordinary filter paper
• B. Freezing point of colloidal solution is lower than true solution at same concentration of a solute
• C. When silver nitrate solution is added to potassium iodide solution, a negatively charged colloidal solution is formed
• D. When excess of electrolyte is added to colloidal solution, colloidal particle will be precipitated

Answer 1

The correct option is B Freezing point of colloidal solution is lower than true solution at same concentration of a solute

(A) Colloidal particles are so small that they can pass through ordinary filter paper. Also, they cannot be seen with ordinary microscope.
(B) Freezing point of colloidal solution is same as that of true solution at same concentration of a solute. The depression in freezing point is colloidal property and depends on the number of solute particles. It is independent of size or shape of solute particles.
(C) When silver nitrate solution is added to potassium iodide solution, a negatively charged colloidal solution is formed. AgI sol is formed which adsorbs negatively charged iodide ions preferentially. However if the order of addition is reversed, i.e, potassium iodide solution is added to silver nitrate solution, the AgI sol will adsorb positively charged silver ions preferentially.
(D) When excess of electrolyte is added to colloidal solution, colloidal particle will be precipitated. Although electrolytes in minute quantities are necessary for the stability of colloids, they cause coagulation of disperse phase if present in large quantities.