Question

Determination of a Molar Mass by Freezing Point Depression: This experiment used Stearic Acid

Experiments done in many first-year chemistry courses. They often use cyclohexane as the solvent and compounds such as p-dichlorobenzene, biphenyl, and naphthalene as the unknown solutes. Describe the advantages of this experiment over those.

Answer 1

This experiment uses cyclohexane, an organic compound that is a liquid at room temperature, as the solvent. The unknown compound is a non-ionic organic molecule; therefore, i is equal to 1. The molecular weight of this unknown compound can be determined by observing the freezing point of a solution of the compound in cyclohexane and comparing it to the freezing point of pure cyclohexane.

The compound cyclohexane has a melting point (or freezing point) of about 6 °C. A series of temperatures of pure cyclohexane are obtained as it cools down from room temperature through its freezing point in an ice bath. These temperatures are then plotted as a function of time. Similarly, temperatures of a solution of the unknown compound dissolved in cyclohexane are obtained as it cools down to the freezing point, which are also plotted

Cyclohexane has large Kf constant. It can To produce a large recordable temperature change for a small amount of solute.