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

  • Page ID
    127149
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    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.