# 4.P: Determination of the Molar Mass by Freezing Point Depression (Pre-Lab)


1. Camphor melts at 179.8oC and has a freezing point depression constant, $$K_{f}$$ = 40 oC/molal. When 0.186 g of an unknown organic solid is dissolved in 22.01 g of liquid camphor, the freezing point of the mixture is found to be 176.7oC. What is the molar mass of the solute?
1. A particular unknown solid depresses the freezing point of PDB ($$K_{f}$$ = 7.1oC/molal) by 3.5oC. If you dissolve the same solid in $$\ce{H2O}$$ ($$K_{f}$$ = 1.86oC/molal) to the same final molality as you had it in the PDB, what would the change in freezing point be?
1. You are instructed to add about 2 g of the unknown solid when determining the freezing point of the solution. Suppose you accidentally add 5 g of solid. Will the measured freezing point of the solution be higher or lower as a result of this mistake? Explain.
1. Cleaning PDB from the test tube after the experiment could be a long and arduous process. Describe the procedure that you will use to clean PDB (and the unknown solid) from your test tube after your experiments are complete.

4.P: Determination of the Molar Mass by Freezing Point Depression (Pre-Lab) is shared under a not declared license and was authored, remixed, and/or curated by Santa Monica College.