Multiple choice

Calculate the freezing point of depression of an antifreeze mixture made up by combining one volume of ethylene glycol (MW = 62, density 1.11 g cm−3) with three volumes of water.

  1. 1.86 K

  2. 3.72 K

  3. 8.1 K

  4. 16.2 K

  5. 32.4 K
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C Correct answer
Explanation

Correct answer. Assume that we use 1 L of ethylene glycol and 3 L of water. The mass of ethylene glycol will be 1.11 kg and that of water will be 3.0 kg. So, the total mass of the solution is 4.11 kg. Number of moles of ethylene glycol = 1110 g / 62 g mol-1 = 17.9 mol Molality of ethylene glycol = 17.9 mol / 4.11 Kg = 4.36 mol Kg-1 Freezing point depression ΔTf = Kf x molality of solution For water, Kf = 1.86 K kg−1 mol ΔTf= (1.86 K kg−1 mol) x (4.36 mol Kg-1) = 8.1 K

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