Question

Lauryl alcohol is a nonelectrolyte obtained from coconut oil and is used to make detergents. A solution of 6.80 g of lauryl alcohol in 0.200 kg of benzene freezes at 4.5 ∘C. What is the approximate molar mass of lauryl alcohol?
What is the approximate molar mass of lauryl alcohol?

Answer 1

Answer:

The approximate molar mass of lauryl alcohol is 174.08 g/m

Explanation:

An excersise to apply the colligative property of Freezing-point depression.

This is the formula: ΔT = Kf . m

First of all, think the T° of fusion of benzene → 5.5°C

ΔT = T° pure solvent - T° fusion solution

Kf for benzene: 5.12 °C/m

5.5°C - 4.5°C = 5.12 °C /m  . m

1°C /  5.12 m /°C = m

0.195 m = molality

This moles of lauryl alcohol, solute, are in 1 kg of benzene, solvent.

I have to find out in 0.2 kg.

1 kg sv ____ 0.195 moles solute

0.2 kg sv ____ (0.195 . 0.2)/1 = 0.039 moles solute

The mass for these moles is 6.80 g, so if I want to know the molar mass, I have to divide mass / moles

6.80 g/ 0.039 moles = 174.08 g/m