T-butyl Alcohol Lab
Marquis Cuffee
Chem 222 L
12/6/13
Abstract
The goals of this experiment were to determine the freezing point of t-butyl alcohol, the molal freezing point constant for t-butyl alcohol, and the molar mass of an unknown substance. The method used to determine the mass of the unknown solute is by plotting data for time vs. temperature. A pipet or buret was used to measure the volume of the liquid unknowns, and then the mass of the sample was calculated using the density from the equation--mass of unknown, g = (volume of unknown, mL) (density of unknown, g mL-1). When observing the cooling curve for the solution, the best straight line drawn through the data points will intersect the portion of the curve representing the cooling of the solute. At that point, the corresponding temperature is the freezing point of the solution, Tf, and the determination of the molar mass relies on the accuracy with which Tf is determined. The results of this experiment were as follows: Kf of t-butyl alcohol was 8.37°C kg/mol, the mean freezing point of the pure solvent was…., the mean freezing point of the alcohol solution was 22.85°C, and the mean molality of the alcohol solution was 1.58 mc, the mean freezing point depression was 13.25°C, the mean molar mass of the unknown was 59.18 g/mol-1, and the percent error of the unknown molar mass was 57.1 %.
Background/Theory
The two factors that determine whether a substance is a solid or liquid are the intermolecular interactions resulting from hydrogen-bonding, dipole-dipole interactions, and/or London forces characteristics of the particular substance; and the amount of kinetic energy by the molecules of the substance, which depends on temperature. When a substance freezes, the molecules have insufficient kinetic energy to overcome those interactions, causing the substance to have a rigid structure. When a nonvolatile solute is dissolved in a solvent, a solution is obtained. The presence of the...