Question

Calculate the molality of a solution that contains 51.2 g of naphthalene, C10Hg, in 500 mL of carbon tetrachloride. The density of CCl4 is 1.60 g/mL.

Answer 1

Moles of naphthalene = Mass(g) / Molar mass

= 51.2 g / 128.17 g/mole

= 0.399 moles.

Mass of solvent (CCl4) = Volume x Density

= 500 mL x 1.60 g/mL = 800 grams.

= 800 mL / 1000 = 0.800 kg.

Now, Molality = Moles / Mass of solvent (kg)

= 0.399 mole / 0.800 kg

= 0.498 m

Molality = 0.498 m