Question #44722

This problem tests the dependency of the van't Hoff factor ($i$) on the degree of dissociation ($\alpha$) for weak electrolytes.

A common trap is assuming isotonicity implies equal molarity ($C_1 = C_2$, leading to $3.6 \text{ g}$) or assuming complete dissociation ($i=2$, leading to $1.8 \text{ g}$).

Furthermore, solving the exact equilibrium expression yields a quadratic with two positive roots; students must apply the physical constraint $\alpha > 0$ (hence $C < iC$) to reject the extraneous root ($0.075 \text{ M}$, leading to $4.5 \text{ g}$).