Mr. Chapman
From Ms. Heidi Patterson
Name: _________________________________
Chemistry 20
The Effect of Temperature on Solubility
Chemistry 20
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 potassium chloride, KCl, in water. After collecting data at
various temperatures, you will plot the data to produce a solubility curve showing how the
solubility of potassium chloride varies with temperature. This, then, can be used to predict the
solubility at other temperatures.
Objective: How does the solubility of KCl in water vary with temperature?
Mr. Chapman
From Ms. Heidi Patterson
Name: _________________________________
Chemistry 20
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 KCl 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 KCl, 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.
Mr. Chapman
From Ms. Heidi Patterson
Name: _________________________________
Chemistry 20
6. Place test tube 1 in the hot-water bath. With a glass stirring rod, stir the KCl mixture until all
the solid has dissolved. At this point, remove the stirring rod and rinse it. Take the thermometer
out of 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, re-dissolve 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.
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.
Mr. Chapman
From Ms. Heidi Patterson
Name: _________________________________
Chemistry 20
Data Table
-
=
-
=

=
-
=

=
-
=



Volume of
Water (mL)
= Concentration Crystallization
Temperature
(g/mL)
(ºC)
Mass of =
Pan (g)
=
Mass of
Sample
(g)

Test Mass of Tube Sample +
Pan (g)
-
=
=
=
Calculations:
1. Plot the solubility of KCl 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.
Mr. Chapman
From Ms. Heidi Patterson
Name: _________________________________
Chemistry 20
Conclusion:
On a separate sheet of paper, write a 3 paragraph conclusion for the entire lab. In the first
paragraph, explain what you did in the lab and why. In the second paragraph, explain what the
results of the experiment were. For the last paragraph, describe what the results mean and what
conclusions you can draw from them. Each paragraph does not need to be long; two or three
sentences are enough as long as you explain fully.