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CH111 Lecture Notes - Lecture 2: Freezing-Point Depression, Cyclohexane, Purified Water

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blackkangaroo274

8 Dec 2017

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Experiment 2: molecular weight determination by freezing point depression. This experiment was conducted in order to determine the molecular weight of an unknown through the use of freezing point depression of cyclohexane. This experiment was completed through the use of the temperature probe, connected to the measurenet system. The density of unknown liquid (0. 7915g/ml) was determined by the ratio of measurement of its mass and a constant volume (10ml graduated cylinder). The specific gravity of unknown solution (0. 7620g/ml) was ratio of the mass of unknown solution and deionized water contained by specific gravity bottle. Using the cooling curve for pure cyclohexane (chart 1&2) the freezing point was measured by measurenet to be 7. 49 c. Using the cooling curve for cyclohexane and unknown mixture solution (chart 3&4) the freezing point was measured to be 4. 44 c. The freezing point depression was calculated to be 3. 05 c.

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Related Questions

DETERMINATION oF MOLAR EXPERIMENT 23 MASS FROM FREEZING POINT DEPRESSION EQUIPMENT AND CHEMICALS: Equipment 600 mL beaker Chemicals Cyclohexane (C Stir plate 100 ml. graduated cylinder Clamp Nonvolatile Unknowns Freezing point apparatus Spin vane 0.1 C Thermometer INTRODUCTION: When a solute is introduced into a pure solvent the newly formed solution will have certain physical properties that are from the solvent. As a of the presence of the the pressure of the solution will be lower than that of the pure solvent. As the vapor pressure is lowered there is a resulting increase in the amount of energy required to reach the boiling point of the solution. Conversely, the solution must cool to a lower temperature before a state change from liquid to solid occurs. These changes in physical properties vapor pressure lowering, boiling point elevation and freezing point depression are collectively referred to as colligative properties. These colligative properties, which also include osmotic pressure, do not depend on the nature of the nonvolatile solute in the solution but rather on the concentration of solute present. Because the properties are independent of the nature of the solute, they may be used to determine other properties of the solute such as molecular weight. The effect of a nonvolatile, nonelectrolyte solute on a pure solvent will be examined by finding the freezing point depression of a cyclohexane unknown so solution. The freezing point of a pure sample of cyclohexane will be determined. Introducing a nonelectrolyte solute should in solution formed to freeze at a lower temperature. This temperature will then be experimentally determined As stated the The molality of the solution dependent on the quantity of solute particles present in solution. (moles solute particles per kilogram of solvent) is directly proportional to the change in temperature between the freezing point of the pure solvent and that of the ATfss Kim The molal freezing point depression constant, K for cyclohexane is equal to 20.00 cfmolal By experimentally determining the freezing point depression of a ohexanel unknown solution, the molal concentration is easily calculated. In turn the molar mass of the unknown olute can be calculated as well Chemistry 132 EXPERIMENT23