Determine the freezing point of a solution that contains 78.8 g of naphthalene (C₁₀H₈, molar mass = 128.16 g mol^-1) dissolved in 722 mL of benzene (d = 0.877 g mL^-1). Pure benzene has a melting point of 5.50 °C and a freezing point depression constant of 4.90 °C m^-1. A) 4.76 °C B) 4.17 °C C) 0.74 °C D) 1.33 °C E) 1.68 °C

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Quizplus · Accepted Answer

First, calculate the molality of the solution: moles of naphthalene = 78.8 g / 128.16 g/mol = 0.615 moles. Mass of benzene = 722 mL * 0.877 g/mL = 633.494 g = 0.633494 kg. Molality = 0.615 moles / 0.633494 kg = 0.970 m. Freezing point depression = 4.90 °C/m * 0.970 m = 4.753 °C. New freezing point = 5.50 °C - 4.753 °C = 0.747 °C, approximately 0.74 °C.

Determine the Freezing Point of a Solution That Contains 78