Question

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 1.2oC on his thermometer. When he added 12.2 g of her sample to the mixture, the temperature, after thorough stirring, fell to –3.0oC. He then poured off the solution through a screen into a beaker. The mass of the solution was 100.5 g. What was the molality of the acetone? (Hint: kf = 1.86 for water) 

Answer 1

$\Delta T =1.2- (-3) = 4.2 \ (^oC)$

$\Delta T=K_Fb$ , $b = \frac{\Delta T}{K_F} = \frac{4.2}{1.86} = 2.258 \ (mol/kg)$