Naphthalene has a molal freezing point constant of 6.9 c/m and a normal freezing point of 80.2 c. Calculate the freezing point of a solution prepared by dissolving 0.0113 mol biphenyl (a molecular solid) in 190.5 g of naphthalene

The freezing point of a solution is 79.8°C

Explanation:

This is about freezing point depression:

Freezing point of pure solvent (T° F pure solvent) → 80.2°C

Freezing point of solution ( T° F solution)

The formula is → T°F pure solvent - T° F solution = Kf . m

Let's determine m (molality) with data given (mol/kg)

We convert the mass of solvent (naphthalene) from g to kg

190.5 g . 1kg/1000 g = 0.1905 kg

molality = 0.0113 mol / 0.1905 kg = 0.059 m . We put the data in the formula.

80.2°C - T° F solution = 6.9°C/m . 0.059m

T°F solution = - (6.9°C/m . 0.059m  -  80.2°C)

T°F solution = 79.8°C