LAB - Solubility of a Salt
PRE-LAB DISCUSSION
The solubility of a pure substance in a particular solvent is the quantity of that substance that
will dissolve in a given amount of the solvent. Thus, solubility must be expressed as quantity of solute
per quantity of solvent at a specific temperature. For most ionic solids, especially salts, in water,
solubility varies directly with temperature. That is, the higher the temperature of the solvent (water),
the more solute (salt) that will dissolve in it.
In this experiment, you will study the solubility of ammonium chloride in water. You will
dissolve different quantities of this salt in a given amount of water at a temperature close to the
water’s boiling point. Each solution will be observed as it cools, and the temperature at which
crystallization of the salt occurs will be noted and recorded. The start of the crystallization indicates
that the solution has become saturated. At this temperature, the solution contains the maximum
quantity of solute that can be dissolved in that amount of solvent.
After solubility data for several different quantities of solute have been collected, the data will
be plotted on a graph. A solubility curve for NH4Cl will be constructed by connecting the plotted
points.
PURPOSE
Collect the experimental data necessary to construct a solubility curve for ammonium chloride in
water.
EQUIPMENT
Balance
Hot plate
Scupula
Test tubes, (4)
Test tube clamp
Striker
MATERIALS
Ammonium Chloride (NH4Cl)
Distilled water
Graduated cylinder, 10-mL
Bunsen Burner
Thermometer
Beaker, 400-mL
Test tube rack
PROCEDURE
While one or two lab partners carry out the instructions in steps 1 through 4, the other partner(s)
should go to step 4.
1. Place a test tube on the balance then zero the balance. Using the scapula, measure out 4.00 g of
ammonium chloride into test tube #1. Record the exact mass in the data table.
2. Repeat step 1 for the following masses of NH4Cl. Add each quantity to the test tube indicated
5.00 g to test tube #2
6.00 g to test tube #3
Record the exact masses for each test tube in the data table.
7.00 g to test tube #4
3. Measure 10.0 mL of distilled water and add it to each test tube. Add the water in such a manner
as to rinse down any solid which might have adhered to the sides to the tests tube.
4. Fill the 400-mL beaker about half full of tap water. Place the beaker on the hot plate and turn the
heat on.
The experiment will be split between your group members. So, two students will carry out procedure
steps 5 -7 for test tubes #1 and 2. At the same time, the other group member(s) will carry out
procedure steps 8-9 for test tubes #3 and 4.
5. Carefully place the test tubes containing the 4.00 g and 5.00 g samples in the water bath and
bring the water to a boil.
6. As the 5.00 g sample sits in the hot water bath, carefully stir its contents with the thermometer
until it all dissolves. DO NOT lift the thermometer out of the solution. Using the test tube clamp,
carefully lift the test tube with the thermometer out of the water bath and hold it in the air. Stir
continuously as it cools and at the instant crystallization starts, observe and record the
temperature in the data table.
7. Repeat Step 6 again now using the 4.00 g sample and record the temperature at the instant
crystallization starts.
8. Heat the test tube containing the 7.00 g sample gently with the Bunsen burner, stirring
continuously and carefully with the thermometer until all the solute dissolves. (Do not lift the
thermometer out of the solution.) DO NOT bring the test tube contents to a boil. Once dissolved,
hold the test tube in the air, stirring continuously as it cools, observe and record the temperature
at the instant crystallization starts.
9. Repeat Step 8 again now using the 6.00 g sample and record the temperature at the instant
crystallization starts.
10. If any doubtful results are obtained, the procedure can be repeated by re-dissolving the salt in the
hot-water bath and allowing it to re-crystallize.
11. Rinse off the thermometer and return it to your table. Pour the contents of the test tubes down the
drain. Clean the test tubes with a test tube brush and thoroughly rinse with water. Turn the test
tubes upside down in the test tube rack to dry.
Name ___________________________________________ Date ____________________ Period _______
Group Member Names____________________________________________________________________
LAB - Solubility of a Salt
OBERVATIONS AND DATA
Test Tube #
Mass (grams)
of NH4Cl
Volume (mL)
of Water
1
10.0
2
10.0
3
10.0
4
10.0
Crystallization
Temperature
(oC)
Use a proportion
to covert to
mass (grams) per
100 mL of water
CALCULATIONS
1. Plot your experimental data (last column in the data table) on the grid provided. Plot grams of solute per
100 mL of water on the y-axis and temperature (oC) on the x-axis. Draw a smooth curve through the
points.
2. Use your solubility curve to determine the solubility of ammonium chloride at 60oC. Show this using a
dotted line on the above solubility curve.
3. Use the given solubility chart to obtain the theoretical solubility in g/100 mL at 60oC. Calculate the percent
error of your experiment. Show all work including the percent error equation, units and chemical formulas.
#3 Answer:
4. Using the given solubility curve, determine the molarity of the solution at 60oC. Show all work including the
molarity equation, units and chemical formulas.
#4 Answer:
5. Using the given solubility curve, classify the following NH4Cl solutions as saturated, unsaturated, or
supersaturated. Explain your answer.
a. 80 grams of NH4Cl dissolved in 100 mL of water at 70oC.
b. 100 grams of NH4Cl dissolved in 200 mL of water at 50oC.
6. How does the solubility of a gas change with increasing temperature? _____________________
Draw a rough sketch showing the general shape of a solubility curve of a GAS. Label the x-axis
and the y-axis. Don’t forget the units.