A student determines the molar mass of acetone, CH3COCH3, by the method used in this experiment. He found that the equilibrium temperature of a mixture of ice and water was 1.2C on his thermometer. When he added 12.2g of her sample to the mixture, the temperature, after thorough stirring, fell to 3.0C. He then poured off the solution through a screen into a beaker. The mass of the solution was 100.5g. What was the freezing point depression? 4.2C 1.8C 4.2C 1.8C