Question

The Van't Hoff factor for sodium phosphate would be:
A. $1$
B. $2$
C. $3$
D. $4$

Answer 1

Hint:The Van't Hoff factor is the ratio of the number of solute particles to the number of particles that are created in a solution once the solute has been dissolved in the solution. This factor is responsible for abnormalities in colligative properties of solution.

Complete step-by-step answer:The van 't Hoff factor $i$ which bears the name of the Dutch chemist Jacobus Henricus van 't Hoff, quantifies how a solute affects related properties like osmotic pressure, relative vapour pressure reduction, boiling-point elevation, and freezing-point depression. The van 't Hoff factor is virtually 1 for the majority of non-electrolytes dissolved in water. The van't Hoff factor for the majority of ionic compounds dissolved in water is equal to the number of discrete ions in the substance's formula unit. Only perfect solutions can claim this as ion pairing occasionally happens in solutions.
Sodium phosphate, having chemical formula $N{a_3}P{O_4}$ , dissociate into $N{a^ + }\,\& \,P{O_4^{3 - }}$ as follows,
 \[N{a_3}P{O_4}\,\, \rightleftharpoons \,\,3N{a^ + } + P{O_3}^{3 - }\]
This implies that $i = 4$ .

Option ‘D’ is correct

Note: Only a small portion of the ions are ever coupled and count as a single particle at any given time. In all electrolyte solutions, ion pairing takes place to some extent. As a result, the measured van't Hoff factor is lower than what a perfect solution would indicate. Where the ions have many charges, the van't Hoff factor variation is most likely to be highest. The van 't Hoff factor $i$ for a solute which undergoes association in solution is less than 1.