g 3.232 g of an unknown solid is dissolved in 363.2 g of benzene. The freezing point of the solution decreases by What is the molar mass of the unknown solid. The freezing point depression constant for benzene is

18.2g/mol is the molar mass of the unknown solid assuming change in freezing point is 2.5°C

Explanation:

In this problem, there is no value of the freezing point depression and the constant for benzene, if:

Freezing point decreases by 2.5°C

And freezing point depression constant for benzene is 5.12°C/m

We can solve the problem as follows:

The freezing point depression is a colligative property that follows the equation:

ΔT = kf*m*ï

Where ΔT is change in temperature (We are assuming is 2.5°C)

Kf is freezing point depression constant for benzene (5.12°C/m)

m is molality of solution (Moles solute / kg solvent)

i is Van't hoff factor (For all solutes dissolved in organic solvents = 1)

Solving for m:

2.5°C = 5.12°C/m*m*1

m = 0.4883m

As molality is defined as moles of solute / kg of solvent and kg of solvent are 0.3632kg:

0.4883m = moles solute / 0.3632kg

0.177 moles of solute

Molar mass is defined as the mass of one mole of substance. Thus, molar mass of an unknown solid is:

3.232g / 0.177 moles of solute =

your answer would be a. 12.5 kg