Question

The freezing point of ethanol CH3CH2OH is -117.30°C at 1 atmosphere. A nonvolatile, nonelectrolyte that dissolves in ethanol is saccharin .

How many grams of saccharin, C7H5NO3S (183.2 g/mol), must be dissolved in 212.0 grams of ethanol to reduce the freezing point by 0.300°C ?

g saccharin.

Answer 1

Depression in freezing point T_f = i K_f m = i x K_f x Wt / M. Wt x 1000 / Wt (solvent)

T_f = Depression in freezing point = 0.300 ^oC

i = no of species = 1

K_f = cryoscopic constant = 2 for ethanol

m = Molality =

weight of solute x 1000 / Molecular weight of solute x weight of solvent

Weight of the solute =?

Weight of the solvent = 212 g

Molecular Weight of solute = 183.2 g

Weight of the solute =?

= T_f x 183.2 x 212 / K_f x 1000

= 0.300 x 183.2 x 212 / 2 x 1000

= 5.826 g

So that 5.826 g of Saccharin is required to decrease the freezing point of ethanol as 0.300 ^oC.