Question

DATA TABLE Mass of lauric acid (9) 8.25 1.09 42.22 C Mass of benzoic acid (g) Freezing temperature of pure lauric acid ('C) Freezing point of the benzoic acid-lauric acid mixture (C)39,11°c Going Further Questions: 1. Calculate molality (m), in molkg, using the formula AT- Kx m. The K value for lauric acid is 3.9°c-kg/mol. 2. Calculate moles of benzoic acid solute, using the molality and the mass (in kg) of lauric acid solvent. 3. Calculate the experimental molecular weight of benzoic acid, in g/mol. 4. Determine the accepted molecular weight of benzoic acid from its formula, C,H,COOH. 5. Calculate the percent error between the experimental and accepted values. 50

Answer 1

Given rightarrow Freezing point of pure lauric acid = 42.82 degree c Freezing point of benzoic acid - lauric acid mixture = 39.71 degree c in freezing point occurs Using increment T = k_f times m rightdoublearrow m = increment T/k_f given k_f = 39 degree c kg/mol (lauric acid) therefore increment T = (42.82 - 39.71) degree c = 3.11 degree c therefore m = 3.11/3.9 mol/kg = 0.7974 mol kg^-1 Moles of benzoic acid solute = molarity times (amount of lauric acid I kg) Given lauric acid = 8.2 g = 8.2 times 10^-3 kg therefore moles of benzoic acid = 0.7974 times 8.2 times 10^-3 = 6.53 times 10^-3 moles