12.
(LAB) Determine the
Determining the Molar Mass
CHM2 molar mass of a solid Colligative
CHM 11/1 of a Solid from the Change of
11/12 3 from the change of 6 Properties of
2 2 Melting Point or Boiling Point
Q3 06 melting point or boiling Solutions
of a Solution
point of a solution
Energy
CHM2
CHM 11/1 Additional Content: Changes in Demonstrating the First Law of
11/12 3 7
2 2 Laboratory Chemical Thermodynamics
Q3 07
Reactions
10. (LAB) practice chemical
CHM1 nomenclature: writing the chemical Chemical
CHM 11/1
11/12 Q1 1 formulas of ionic compounds; 5 Molecules Nomenclature
1 2
05 naming ionic compounds from Worksheet
formulas
CHM1
CHM 11/1 The Mole
11/12 Q1 1 Additional Content: Laboratory 6 Moles Worksheet
1 2 Concept
06
Carefully adjust the height of the thermometer so the entire mercury bulb is immersed in the liquid but so that there is
room for the stir bar beneath it.
2
Carefully rotate the split stopper so the graduations on the thermometer are visible through the split. Make sure the
utility clamp is located so that you can easily read the thermometer.
3
Prepare an ice-water slurry. Fill your 250-mL beaker with ice, add enough water to fill the spaces, and stir. The
temperature should be within a degree or two of 0°C
1. Place 10- mL of distilled water in an 8-inch test tube. Insert the entire apparatus and
as shown in the figure below. Note: Make sure that the thermometer bulb is
immersed in the liquid.
Freezing point of pure t-butanol:
1. Place a 150 ml beaker on a top loader balance and tare it.
2. Place a clean, dry 25 x 150 mm test tube in the beaker and record the mass in the data
table, line 1.
3. Fill the test tube about half full with t-butanol, reweigh and record this mass in the data
table, line 2. Place the beaker and test tube aside for now.
Freezing point of solutions:
1. Weigh 0.25g of unknown solid and transfer into test tube used in part A.
2. Reheat the test tube as before to about 40 °C using hot plate. The unknown solid must be
completely dissolved in the tet-butanol.
3. Use the wire stirrer to aid the dissolution of the solute, if needed.
4. As before, once the temperature is about 40 °C, transfer the test tube to the ice-water
bath. More ice may be added, if needed.
5. Begin stirring and take temperature readings every 15 seconds until the solution has
solidified. When the solution has solidified so that you can no longer stir it, stop trying to
stir, but continue to record the temperature every 15 seconds for one more minute.
Explain why the freezing point of a pure solvent is constant, whereas the freezing point of a solution
decreases with steady cooling.
The cooling curve for the solution does not reach a plateau but continues to decrease slowly as the
cyclohexane gradually freezes leaving behind solutions of higher concentrations. The freezing point of
the solution is determined from the graph by drawing two straight lines through the data points above
and below the freezing point.
Construct a plot of temperature (y-axis) against time (x-axis) for the pure t-butanol and for
the solution analyzed.
In this case we must draw a trend line through the data points corresponding to the cooling of the liquid
and a trend line through the data points corresponding to the freezing of the liquid. The temperature at
the point where those two lines intersect is the freezing point of the solution.
a. The freezing points of t-butanol reach a plateau at its freezing point. Extrapolation of the
plateau to the temperature axis determines its freezing point.
b. For the t-butanol solution, it does not reach a plateau but continues to decrease slowly. The
freezing point of the solution is determined by drawing draw a trend line through the data
points corresponding to the cooling of the liquid and a trend line through the data points
corresponding to the freezing of the liquid. The temperature at the point where those two lines
intersect is the freezing point of the solution
c. Calculate the molar mass of the unknown solid by finding the difference in freezing points
between the t-butanol and t-butanol solution.
