A mixture of salt and ice is used to chill the contents of old-fashioned, hand-operated ice cream makers. What is the melting point of a mixture of 1.00 lb of sodium chloride and 16.00 lb of ice if exactly half the ice melts? Assume ideal behavior and that all the sodium chloride dissolves in the melted ice water. K_f(water) = 1.86°C/m A) -8°C B) -11°C C) -12°C D) -21°C E) -15°C

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Quizplus · Accepted Answer

The correct answer is A because the melting point of the mixture is -8°C. This is because the addition of sodium chloride to ice lowers the freezing point of the mixture. The freezing point depression is calculated using the formula ΔT_f = K_fm, where ΔT_f is the change in freezing point, K_f is the freezing point depression constant for the solvent (water), and m is the molality of the solution. In this case, the molality of the solution is 1.00 lb of sodium chloride / (16.00 lb of ice + 8.00 lb of melted ice) * (1 mol / 58.44 g) = 0.34 mol/kg. Therefore, the change in freezing point is ΔT_f = 1.86°C/m * 0.34 mol/kg = -0.63°C. The melting point of the mixture is therefore -8°C + (-0.63°C) = -8.63°C, which is rounded to -8°C.

A Mixture of Salt and Ice Is Used to Chill