Molecular weight of Benzoic acid = 122.12 g Mass of Benzoic acid in solution = 1

Question

Molecular weight of Benzoic acid = 122.12 g

Mass of Benzoic acid in solution = 1.221 g

No.of moles of benzoic acid = 1.221/122.13 = 0.01 moles.

Weight of solvent (Lauric acid ) in Kg = 0.008 Kg.

Molality = moles of solute/weight of solvent in Kg .

Molality = 0.01/0.008 = 1.25 m .

Tf = Kf × m.

Where Tf = depression in freezing point

Kf = molal depression constant = 3.9oC/m

m = molality = 1.25 m.

Tf = 3.9 × 1.25 = 4.875oC

Tf = Tof - Tf

Where Tof = freezing point of pure solvent

Tf = freezing point of solution.

Tof - Tf = 43.2oC - Tf = 4.9oC

Tf = 43.2 -4.9 = 38.3oC

Explanation / Answer

V) (8 points) What is the freezing point temperature for a solution of 1.221 g of benzoic acid (CHCOOH) in 000 g of lauric acid? For lauric acid. Cll(cilhocooll, the normal freezing point is 432°C, and Kr value is 3.9 °C/m. 2

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