Name _____________________________________________________ PD_____ Date_________________________________
Effect of Temperature on Solubility
The solubilities of gases always decrease 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.
Hypothesis: How does the solubility of KCl in water vary with temperature?
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Procedure:
1. Make sure test tubes are labeled 1 – 5. Measure masses of test tubes.
2. Use weigh boat to measure out KCl.
Test tube 1
2.5 g
Test tube 2
2.3 g
Test tube 3
2.0 g
Test tube 4
1.8 g
Test tube 5
1.5 g
DO NOT put unused KCl back in the original container. Discard unused KCl in waste beaker.
3. Fill your large beaker ¾ full of water and place on hot plate. Place a thermometer in the water and
begin heating while you proceed with step 5. Heat the water to 90ºC. (Make sure water does not boil
during entire lab!)
4. Put 5.1 mL of water in a 10 mL graduated cylinder. Add this water to test tube 1. Repeat this process,
adding 5.1 mL of water to each of the test tubes.
5. Place test tube 1 in the hot-water bath. With a glass stirring rod, stir the KCl in test tube until it has
dissolved. At this point, remove the stirring rod and rinse it. Take the thermometer out hot water
and quickly wipe off, then place it into the test tube while it is still warm.
6. Carefully hold the test tube up to a light. Watch for the very first signs of crystallization, and then
immediately record the temperature. If you miss the first sign of crystallization, you will have to
repeat step 5 until you are able to determine the temperature at which the crystallization begins.
Record this in the data table.
7. Repeat steps 5 and 6 for all five test tubes. For test tube 5, you will need to place it in an ice bath after
the KCl has dissolved. Simply place a small handful of ice cubes in a beaker and fill half way with
water.
Data:
Mass of weighing pan: _______________
Test
tube
1
Mass of test tube (grams)
Mass of KCl used (grams)
Temperature when
crystallization occurs in ̊C
2
3
4
5
Calculations:
Test tube 1: You have 2.5 g of KCl in 5.1 mL of water. Set up a proportion to determine how many
grams of KCl you would have if there is 100 mL of water.
2.5 g =
x .
5.0 mL
100 mL
a. Repeat for test tubes 2 – 5.
b. Use these values to plot a graph.
Conclusions:
1. Plot the solubility of KCl on graph paper. On the y axis, label “solubility of KCl in g/100 mL H2O”.
On the x axis, label “Temperature in ºC”.
2. Look up the values of solubility of potassium chloride.
a. For each mass of KCl used in this lab, look up the temperatures at which the sample should
have crystallized. Determine your percent error for each sample.
3. What happens to the solubility of KCl in water when the temperature increases? When
temperatures decreases? Was the hypothesis supported?
BONUS: The dissolved oxygen content of water is very critical to marine life. Investigate the
solubility of oxygen in water as a function of temperature, and couple that with an investigation of
the oxygen needs of various kinds of aquatic animals. Such studies relate to “thermal pollution,” a
serious concern near power plants and other industries that release heated water into streams
and rivers. Write a report on this. Pay particular attention to any such problems in your area.