Question

The freezing point of a solution prepared by dissolving 150 × 10–3 g of caffeine in 10.0 g of camphor is lower by 3.07°C than that of pure camphor (Kf = 39.7°C/m). What is the molar mass of caffeine?

Answer 1

Answer:

Molar Mass=193.9738 g/mol

Molar Mass≅194g/mol

Explanation:

Consider the formula:

m=ΔT/K_{f}

where:

ΔT is freezing point depression

K_{f} is freezing point depression constant

m is the morality=(moles of solute/kg of solvent)

Now:

$m=\frac{3.07}{39.7}$

$m=0.07733 moles of solute/kg of solvent$

Now:

0.07733 (moles of solute/kg of solvent) *0.010 kg of solvent

$7.733*10^{-4}$ moles of solute(Caffeine)

Molar mass = Mass of solute/moles of solute

Molar Mass=$\frac{150*10^-3}{7.733*10^{-4} }$

Molar Mass=193.9738 g/mol

Molar Mass≅194g/mol