0.1 Colligative properties and ice cream  (Page 2/3)

The solvent we will use in this experiment is tert-butanol (IUPAC name: 2-Methyl-2-propanol) also called tert-butyl alcohol. It has a characteristic camphor type smell and is used in paint removers, to boost octane in gasoline and in perfumes. Its structure is given in Figure 2.

In this experiment we will measure the freezing temperature of pure tert-butanol, then measure the freezing point of a solution containing 3-5 grams of ethylene glycol added to tert-butanol. The difference in freezing temperatures for the two solutions gives the Δ T in Equation 1. Since the purpose of this experiment is to find the molecular weight of the solute, Equation 1 can be rewritten to include molecular weight of the solute:

For this experiment, use a Kf for tert-butanol of 8.37°C/m.

The only unknown in equation 2 is the molar mass of the solute. If you algebraically rearrange Equation 2, you can then solve for molar mass. This algebraic manipulation is left as an exercise for you to complete.

SAFETY PRECAUTIONS: Ethylene glycol and tert-butanol are safe if handled properly, but are mildly poisonous if swallowed. These chemicals can also cause allergic reactions with skin contact. Wear plastic gloves when pouring and measuring these chemicals. If you spill any on your hands, wash immediately with soap and water. Be sure to wear safety glasses at all times during this experiment.

Experimental Procedure

Part 1: Freezing point of tert-butanol

• Open the MicroLab Program by clicking on the shortcut to MicroLab.exe tab on the desktop.
• On the “Choose an Experiment Type” tab, enter a name for your experiment, and then double click on the MicroLab Experiment icon.
• Click “Add Sensor”, choose sensor = Temperature (thermistor).
• To choose an input, click on the red box that corresponds to the port which the thermistor is connected.
• Choose label = Thermistor, sensor units = ° C, click next.
• Click “Perform New Calibration”.
• Click “Add Calibration Point” and place the thermistor and a thermometer in an ice water bath. Wait until the temperature is constant, then read the temperature on the thermometer and enter that value into the “Actual Value” box in MicroLab and hit “ok”.
• Again, click “Add Calibration Point” and place the thermistor and a thermometer in a warm water bath. Wait until the temperature is constant, then read the temperature on the thermometer and enter that value into the “Actual Value” box in MicroLab and hit “ok”.
• Under Curve Fit Choices, click on “First order (linear)” and then “Accept and Save this Calibration”, when prompted to enter units, enter as “deg C”. Save as your name-experiment data.
• Click “Add Sensor”, choose sensor = Time
• Choose an input, click on the red box that corresponds any of the timers.
• Label = Time 1, click next, click finish.
• Left click on thermistor and drag to: the Y-axis over “data source two”, column B on the spreadsheet, and the digital display window.
• Left click on time and drag to: the X-axis over “data source one”, column A on the spreadsheet, and the digital display window.
• When ready to obtain data, click start.
• Take a clean, dry 10cm test tube, and fill it half-way with tert-butanol, dispensed by your TA.