Chem 20
The Effect of Temperature on Solubility
Theory: Hot tea can dissolve more sugar than iced tea, and warm water dissolves less oxygen
than cold water. The maximum amount of any solute that can dissolve in a given amount of
solvent is called its solubility, and this depends on the temperature.
The solubilities of gases always decreases with increasing temperature. For liquids and solids, solubilities generally increase with
increasing temperature, as is the case with sugar in tea. However, there are a number of exceptions to this, two examples being
cerium sulfate, Ce2(SO4)3, and lithium carbonate, Li2CO3 For these ionic solids, solubility decreases with increasing temperature.
In this activity, you are to determine the effect of temperature on the solubility of ammonium chloride, NH4Cl, in water. After
collecting data at various temperatures, you will plot the data to produce a solubility curve showing how the solubility of
ammonium chloride varies with temperature. This, then, can be used to predict the solubility at other temperatures.
Chem 20
Objective: How does the solubility of NH4Cl in water vary with temperature?
Procedure:
1. Label test tubes 1 through 5, respectively.
2. As accurately as possible, determine the mass of a weighing pan. Record. Use this to measure out KCl.
3. To each of the test tubes, 1 through 5, you want to add samples of NH4Cl having the following masses: 2.50g, 2.30 g, 2.00 g,
1.80 g and 1.50 g. It is not necessary that your samples be exactly these masses; it is necessary that the values be within 0.05 grams,
and that you determine the masses as accurately as possible. Use a spatula to add or remove small amounts of the solid from the
weighing pan. If you need to remove some NH4Cl, do not return it to the original container.
4. Fill the large beaker about ¾ full of water to use as a hot-water bath. Place the beaker on a piece of wire gauze on the ring or
hot plate (depending on which we use). Place a thermometer in the water and begin heating while you proceed with step 5. The
goal is to heat the water to 90 ºC.
5. Put 5.1 mL of distilled water in a 10 mL graduated cylinder. Use a medicine dropper to bring the bottom of the meniscus right to
the 5.1 mL line. The extra 0.1 mL is to correct for drops left behind when the water is transferred to a test tube. Add this water to
test tube 1. Repeat this process, adding 5 mL of water to each of the test tubes.
6. Place test tube 1 in the hot-water bath. With a glass stirring rod, stir the NH4Cl mixture until all the solid has dissolved. At this
point, remove the stirring rod and rinse it. Take the thermometer out the hot water bath, quickly wipe any excess drops of water
from it, and place it into the test tube while it is still warm.
7. Carefully hold the test tube up to a light. Watch for the very first signs of crystallization, and then immediately note the
temperature. If crystallization begins too quickly, or you do not catch it the instant it begins, redissolve the precipitate and repeat
until you are able to determine the temperature at which the crystallization begins. Record this in the data table. If you are
working with a partner, the second person should be setting up test tube 2.
Chem 20
8. Repeat steps 6 and 7 for all five test tubes. For test tube 5, it will be necessary to use an ice bath to effect crystallization. Simply
place 3 or 4 pieces of ice in a beaker and fill half way with water.
Data Table (5 marks)
Test
Tube
Mass of
Sample +
Pan (g)
-
Mass of
Pan (g)
=
Mass of
Sample
(g)
 Volume of Water =
(mL)
-
=

=
-
=

=
-
=
-
=
-
=



Concentration
(g/mL)
Crystallization
Temperature
(ºC)
=
=
=
Calculations:
1. Plot the solubility of NH4Cl on the y axis in g/100 mL H2O versus the temperature in ºC on the x axis. DO NOT connect the dots,
but instead draw a smooth curve passing through or coming as close as possible to your data points. (10 marks)
2. Bonus: Look up the value of the solubility of ammonium chloride. The temperature at which the measurement was made is
usually given. From your graph, determine the value at the same temperature as you found. Determine a percent error by dividing
the difference between the book value and your value by the book value, and then multiplying by 100 %. (3 marks)