The molecular weight of an organic compound was determined by measuring the freezing point depression of a benzene solution. A 0.500 g sample was dissolved in 50.0 g of benzene, and the resulting depression was 0.42°C (kf (benzene) = 5.065°C/m). What is the approximate molecular weight of the compound?

The molar mass of the sample is 120.6 g/mol

Explanation:

To calculate the depression in freezing point, we use the equation:

Or,

where,

= depression in freezing point = 0.42°C

i = Vant hoff factor = 1 (For non-electrolytes)

= molal freezing point elevation constant = 5.065°C/m

= Given mass of solute (sample) = 0.500 g

= Molar mass of solute (sample) = ? g/mol

= Mass of solvent (benzene) = 50.0 g

Putting values in above equation, we get:

Hence, the molar mass of the sample is 120.6 g/mol