Question

When 63.4 g of glycine (C2HNO2 are dissolved in 700. g of a certain mystery liquid X, the freezing point of the solution is 7.9 °C lower than the freezing point of pure X. On the other hand, when 63.4 g of iron(III) chloride are dissolved in the same mass of X, the freezing point of the solution is 13.3 °C lower than the freezing point of pure X Calculate the van't Hoff factor for iron(III) chloride in X.

Answer 1

Answer:  The van't Hoff factor for iron(III) chloride in X is 3.64

Explanation:

Depression in freezing point is given by:

$\Delta T_f=i\times K_f\times m$

$\Delta T_f=7.9^0C$ = Depression in freezing point

i= vant hoff factor = 1 (for non electrolyte)

$K_f$ = freezing point constant = $k^0C/m$

m= molality

$\Delta T_f=i\times K_f\times \frac{\text{mass of solute}}{\text{molar mass of solute}\times \text{weight of solvent in kg}}$

$7.9^0C=1\times k_f\times \frac{63.4g\times 1000}{75.07g/mol\times 700g}$

$k_f=6.55^0C/m$

b) $\Delta T_f=i\times K_f\times \frac{\text{mass of solute}}{\text{molar mass of solute}\times \text{weight of solvent in kg}}$

$13.3^0C=i\times 6.55\times \frac{63.4g\times 1000}{162.2g/mol\times 700g}$

$i=3.64$

Thus the van't Hoff factor for iron(III) chloride in X is 3.64