Molar Mass Determination by Freezing Point Depression
Name:______Section: ______
Date: ______
Purpose (goal of the experiment):
DATA
- Determining the Freezing Point of t-Butyl Alcohol
Mass of t-butyl alcohol, tube and beaker:______g
Mass of test tube and beaker:______g
Mass of t-butyl alcohol:______g
Freezing point of t-butyl alcohol:______°C ______°C
Average freezing point of t-butyl alcohol: ______°C
Attach the temperature – time graphs as directed in the lab manual (both trials may be plotted on the same graph).
Show how you determined the freezing points from the graph (both trials):
- Determining Kf of t-Butyl Alcohol
Mass of t-butyl alcohol:______g
Mass of solute (ethyl acetate):______g
Moles of solute (ethyl acetate):______mol
Molality of the solution:______mol/kg
Freezing point of t-butyl alcohol solution:______°C ______°C
Freezing point depression:______°C ______°C
Kf of t-butyl alcohol:______°C/molal ______°C/molal
Average Kf of t-butyl alcohol:______°C/molal
Attach the temperature – time graphs as directed in the lab manual (both trials may be plotted on the same graph).
Show how you determined the freezing point from the graph (one of the two trials):
- Determining the Molar Mass of the Unknown(write the unknown # ______)
Mass of t-butyl alcohol:______g
Mass of solute (unknown):______g
Freezing point of t-butyl alcohol solution:______°C ______°C
Freezing point depression:______°C ______°C
Molality of the solution:______mol/kg ______mol/kg
Molar mass of the unknown:______g/mol ______g/mol
Average Molar mass of the unknown:______g/mol
Attach the temperature – time graphs as directed in the lab manual (both trials may be plotted on the same graph).
Show how you determined the molar masses (both trials):
Post Lab Questions
1.A student, following the procedure for this experiment, used water as the solvent and encountered some interesting situations. Comment on the effect, if any, of the following:
(a) The unknown, a white powder, failed to dissolve in the solvent.
(b) The student tried a different solid unknown. This unknown dissolved, but bubbles were seen escaping from the solution after the addition of the solid unknown.
(c) As the student was setting up the apparatus to measure the freezing point of the unknown solution, the thermometer rolled off the bench and broke. The student obtained a new thermometer and continued with the Part 3 of the experiment.
2. Suppose you are at the ocean and want to quickly cooldown canned drinks for the afternoon. You have a cooler, bottled water and a bag of ice. What is the fastest way to cool your drinks?