Question

1.80 g of solute A was dissolved in 62.5 cm3 of ethanol and freezing point of the solution was found to be 155.1 K. The molar mass of solute A is ____ g mol-1.
[Given : Freezing point of ethanol is 156.0 K, Density of ethanol is 0.80 g cm-3, Freezing point depression constant of ethanol is 2.00 K kg mol-1]

Answer 1

$ΔT_f=k_fm$

$0.9=\frac {2×1.8×1000}{62.5×0.8×M}$

Then, the molar mass of solute A,

$M=\frac {2×1800}{62.5×0.8×0.9}$

$M=80$ g/mol

So, the answer is $80$.