High School

Calculate the molality of a solution that contains 51.2 g of naphthalene, [tex]C_{10}H_{8}[/tex], in 500 mL of carbon tetrachloride. The density of [tex]CCl_{4}[/tex] is 1.60 g/mL. (Molecular weight of naphthalene = 128.17 g/mol)

A. 0.250 m
B. 0.500 m
C. 0.750 m
D. 0.840 m
E. 1.69 m

Answer :

To calculate the molality of the solution, we need to find the moles of naphthalene and the mass of the solvent Therefore the correct option is A.

The moles of naphthalene can be calculated using the given mass and the molecular weight of naphthalene: moles of naphthalene = mass of naphthalene / molecular weight of naphthalene = 51.2 g / 128.17 g/mol = 0.3998 moles (approximately)

The mass of the solvent can be calculated using the density of carbon tetrachloride: mass of CCl4 = volume of CCl4 x density of CCl4 = 500 mL x 1.60 g/mL = 800 g Now, we can calculate the molality using the formula: molality = moles of solute / mass of solvent (in kg) = 0.3998 moles / 0.800 kg = 0.49975 m (approximately)

Hence the correct option is A.

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