Question

The apparent molar mass of $PC{l_5}$ on dissociation shows on lower value. If true enter 1. If false enter 0.

Answer 1

To solve this question, you must recall the abnormalities in molar mass when calculated using colligative properties given by the Van’t Hoff factor. Colligative properties are those properties whose value depends solely on the number of particles of solute present in the solvent.
Formula used: $i = {\text{ }}\dfrac{{{\text{Observed colligative property}}}}{{{\text{Normal colligative property}}}} = \dfrac{{{\text{Normal molecular weight}}}}{{{\text{Observed molecular weight}}}}$
Where, $i$ is the Van’t Hoff factor

Complete step by step answer:
Inorganic acids and ionic solutes undergo dissociation in aqueous medium. They form cations and anions within the solutions. We know that phosphorus pentachloride undergoes dissociation to form phosphorus trichloride and chlorine. As the number of particles in the solution increases, we will note an increase in the colligative properties than those calculated on the basis of undissociated single molecules.
Colligative properties vary inversely with the molecular mass of the solute, thus, there will be a decrease in the molar mass calculated.

So, the statement is true, enter 1.

Note:
There are four colligative properties, namely, relative lowering of vapour pressure, elevation in boiling point, depression in freezing point and osmotic pressure. All of the four colligative properties can be used to determine molar masses of non-volatile solutes. We calculate colligative properties only for dilute solutions which can be assumed as an ideal solution.
However, sometimes, the molar masses of non- volatile solutes calculated from colligative properties are not accurate mainly due to three reasons, which are, the solution may not behave as an ideal solution, i.e., it may not be a dilute solution, or the solute particles may undergo association or dissociation in the solution.