Question

Molar Mass by Freezing Point Depression.

What is the effect on your calculated molar mass if the following happened:

a. 2.000g of an unknown solute was added to the solvent instead of 1.200g as directed, but 2.000g was used in the calculations. (All 2.000g dissolved in the solvent.)

b. The unknown solute reacted with the t-butanol solvent and fragmented into two approximately equal sized molecules.

c. Too much solid was put into the solvent- it dissolved when hot, but much of the solid precipitated out of solution before reaching the freezing point.

Answer 1

a. We have added 2 g instead of 1.2 g

Thus the molality will be higher than expected and the molar mass will be lower than the correct answer

b. Since depression in freezing point is a colligative property and as a result of the reaction number of solvent molecules will be higher. Thus the calculated molality will be higher than expected and the molar mass will be lower than the correct answer

c. If any precipitation of solvent results in the decrease in molality and the calculated molar mass will be higher than the correct answer