Name ___________________________________________ Block _________ Date ______________________
Advanced Chemistry & Physics
Lab #16: Temperature and Solubility
LAB ASSIGNMENT:
You will explore the effect that a change in temperature has on the solubility of a typical ionic salt. You
will study the solubility of potassium nitrate in water by adding different quantities of the salt to a fixed
(constant) mass of water at a temperature close to the boiling point of the solvent. Each solution will be
allowed to cool and the temperature at which crystals begin to appear will be noted; this is the signal that the
system has cooled to the saturation point. Data for various combinations will be collected and a plot of
concentration vs. saturation temperature will be prepared.
Materials:
4 test tubes
thermometer
balance
100 mL beaker
test tube holder
goggles
distilled water
4 g KNO3
Procedure:
1. Create a data table with the following headings:
Test Tube
Mass of KNO3
Mass of H2O
gKNO3 / g H2O
Crystallization
Temp oC
Concentration
of solution
g/100 g H2O
2. Prepare a water bath with the 100 mL beaker.
3. Label four test tubes A, B, C, D and add the following quantities of potassium nitrate to each. Record the
exact mass of each in your data table.
Tube
Mass of KNO3(s)
0.35 – 0.45 g
A
0.75 – 0.85 g
B
1.10 – 1.20 g
C
1.50 – 1.60 g
D
4. Use a pipette to add 20 drops of water to each tube. Weigh each tube again and determine the mass of water
in each. If the mass increase due to the addition of water does not fall in the range of 0.80 – 1.10 g add a few
more drops. Record the mass of water in each tube in your data table.
5. Calculate the ratio of mass of solute to mass of water in the data table.
6. Place all four labeled test tubes in the water bath with your thermometer in tube D. Stir the mixture in D
gently, using an up-and-down motion of the thermometer until all the solid in that tube dissolves completely.
7. Remove the beaker from the heat source and remove test tube D only from the beaker and allow the tube and
contents to cool as you watch for the first sign of crystallization. (Moving the thermometer gently up and
down will ensure constant, even cooling and encourage crystal formation). The instant you see the
formation of colorless crystals in a colorless solution (they will not be easy to detect) record the temperature
in your data table.
8. Repeat step 7 with tube C, then tube B and so on until all four tubes are done. Be sure to clean the
thermometer before you place it in the next tube!
Analysis and Conclusion
1. Use the data from column 3 of the data table to determine the concentration of each saturated solution in
grams of solute per 100 grams of water. Show your calculation for tube A. Record all concentrations in the
last column of the data table..
2. Plot a graph of solubility of KNO3 in grams/100 g of water v. temperature. Label the axes of your graph and
give it an appropriate title. Draw the best smooth curve through the points, extending your graph from 0oC to
100oC.
3. Using your graph, determine the solubility of KNO3, in 100 g H2O at:
a. 30oC
b. 70oC
c. 0oC
d. 90oC
4. From your graph, determine the temperature at which each of the following mixtures of potassium nitrate
in water would be saturated solutions. Use your graph, do not calculate the values.
a. 45 g KNO3 in 100 g H2O
b. 20 g KNO3 in 100 g H2O
c. 25 g KNO3 in 25 g H2O
d. 100 g KNO3 in 250 g H2O
5. Define the terms saturated, unsaturated and supersaturated as they apply to solutions. Use complete
sentences.
6. Classify the following solutions as saturated, unsaturated or supersaturated based on your graph. Defend
your answers. Note that c and d require you to convert from the concentrations given to g/100 g H2O before
you can refer to your graph.
a. 75 g KNO3/100 g H2O @ 40oC
b. 60 g KNO3/100 g H2O @ 50oC
c. 100 g KNO3/75 g H2O @ 80oC
d. 175 g KNO3/250 g H2O @ 40oC