Answer:
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 =
