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 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 particles will be precipitated.

Answer 1

Hint: Colloids are tiny particles which are uniformly dispersed in a dispersion medium. Nature of interaction between the dispersed phase and the dispersion medium indicate various properties about the colloidal solution formed.

Complete step-by-step answer:
A) Colloids are tiny particles which can easily pass through an ordinary filter. A special microscope is required to view them as they cannot be viewed through a naked eye or through an ordinary microscope.
So, this statement is true.

B) The freezing point of a substance is the temperature at which the vapour pressure of a substance in its liquid phase is equal to the vapour pressure in its solid phase. Thus, the colloidal solution and the true solution have the same or higher freezing point at the same concentration of solute. The depression in freezing point depends upon the number of solute particles and is independent of the shape and size of the solute particles.
So, this statement is false.

C) When a silver nitrate solution is added to a colloidal solution, silver iodide salt is formed as a product which can absorb negatively charged iodide${I^-}$ ions.
$AgN{O_3} + KI \to AgI$
So, this statement is true.

D) Addition of electrolyte results in stability of the colloidal solution and small quantity of electrolyte causes coagulation which is the process of settling of colloidal particles and on adding excess electrolyte to colloidal solution the colloids precipitate as the colloids interact with ions carrying opposite charge.
So, this statement is true.

Now we know that the answer is that statement (B) is false.

Note: The presence of equal and same charges on colloidal particles provides stability to the colloidal solution. The repulsive forces between charged particles having the same charge prevent aggregation when they come within each other’s proximity.