Experiment #5 Freezing Point Depression
Purpose: Determine the molecular weight of an unknown by freezing point depression.
Background: Vapor pressure is the force on the sides of a container by the molecules that
are exerted by a substance. Solutions lower vapor pressure. Less solvent molecules can
become vapor because there are solute molecules taking up space on the surface.
1) Clamp a large pyrex test tube to the ring stand.
2) Get 15 mL of cyclohexane in a graduated cylinder.
3) Record exact volume in notebook.
4) Pour cyclohexane into test tube.
5) Fit with a stopper and a thermometer.
***Thermometer must be centered in the cyclohexane***
1) Get two 600 mL beakers, a 250 mL beaker, and another thermometer.
2) Put 600 mL of ice in one of the big beakers.
3) Put 100 mL of NaCl solid in the small beaker.
4) Transfer about 300 mL of ice into the second big beaker.
5) Add NaCl solid and stir. (want 15 C)o
III. Bring a timer to class to measure seconds.
1) Immerse the tube of cyclohexane in the cold bath.
2) Immediately record temperature. (t ) 0
3) Record the temperature every 20 seconds.
a. You should