Question

The degree of dissociation of monobasic acid is 0 3 By what percent is the observed depression in freezing point greater than the calculated depression in freezing point ?

Answer 1

The observed depression in freezing point is given by the equation:
ΔT_f(obs) = K_f × m × i
where ΔT_f(obs) is the observed depression in freezing point, Kf is the freezing point depression constant of the solvent, m is the molality of the solution, and i is the van't Hoff factor. For a monobasic acid, the van't Hoff factor is equal to 2 (assuming complete dissociation).
The calculated depression in freezing point is given by the equation:
ΔT_f(calc) = K_f × m
where ΔT_f(calc) is the calculated depression in freezing point.
The percent difference between the observed and calculated depressions in freezing point can be calculated as follows:
% difference = \([\frac{(ΔTf(obs) - ΔTf(calc))} { ΔTf(calc)}]\) × 100
Substituting the values, we get:
% difference = \([\frac{(K_f × m × i - K_f × m) }{ (K_f × m)}]\) × 100
% difference = [\(\frac{(2 - 1) }{1}\)] × 100 (since i = 2 for a monobasic acid)
% difference = 100%
Therefore, the percent difference between the observed and calculated depressions in freezing point is 100%. This means that the observed depression is twice the calculated depression, which is expected since the degree of dissociation is 0.3, indicating that only 30% of the acid molecules dissociate into ions, leading to a lower concentration of solute particles and a smaller depression in freezing point than would be expected for a fully dissociated acid.
Answer. 30

Answer 2