Calculate the molality of a solution

Question

Calculate the molality of a solution that contains 51.2 g of naphthalene, C10H8, in 500 mL of carbon tetrachloride. The density of CCl4 is 1.60 g/mL.

Answer 1

Molality is moles of solute per kg of solvent

moles of solute = 51.2 g x 1 mole/128 g = 1.18 moles naphthalene (molar mass of C10H8 = 128 g/mol)

kg of solvent = 500 ml x 1.60 g/ml = 800 g = 0.800 kg

molality (m) = 1.18 moles/0.800 kg = 1.48 molal