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Date done:
Lab: Solubility Curves
Introduction
You have seen and used solubility curves earlier in this unit. In this activity, you will collect
experimental data to construct a solubility curve for succinic acid (C4H6O4), a molecular compound.
Safety
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The succinic acid that you use is slightly toxic if ingested by mouth, so be sure to wash your
hands thoroughly at the end of the lab.
Never stir a liquid with a thermometer. Always use a stirring rod.
At the end of the lab, dispose of the succinic acid crystals in the large beaker in the hood.
Leave the large test tubes in the container provided.
Materials
4 16 x 125 mm test tubes
glass stir rod
test tube rack
thermometer
25- or 50-mL graduated cylinder
400 mL beaker
hot plate
4 g succinic acid
ice
balance
Procedure
1. To make a water bath, add approximately 300 mL water to a 400-mL beaker. Heat the beaker,
with stirring, to either 45°C, 55°C, or 65°C, as assigned. Carefully remove the beaker (using hot
hands or beaker tongs) when it reaches the desired temperature. Do not allow the water-bath
temperature to rise more than 5°C over the temperature you have chosen. Return the beaker to the
hot plate as needed to maintain the appropriate water-bath temperature.
2. Place between 2.0 and 2.1 g succinic acid in each of two test tubes. It is not important exactly how
much you use, as long as you have within this range.
3. Add 10.0 ml distilled water to each test tube.
4. Place each test tube in the water bath and take turns stirring the succinic acid solution with a glass
stirring rod every 30 seconds for 7 minutes. Make sure the water bath stays close to the desired
temperature.
5. At the end of 7 minutes, carefully decant the clear liquid from each test tube into a separate, empty
test tube, using the stirring rod to guide as you decant.
6. Pour the hot water from the beaker into the sink and fill the beaker with water and ice.
7. Place the two test tubes containing the clear liquid in the ice bath for 5 minutes. Stir the liquid in
each test tube gently once or twice and tap the side of each test tube to cause the crystals to settle
evenly on the bottom of the test tubes. (This is a good time to start cleaning up!)
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8. While the tube is still cold, measure the height of the crystals collected in millimeters. Record the
average height for your two test tubes o the board.
9. Rinse the succinic acid crystals from the test tubes into the designated collection beaker. Make
sure your lab area is clean.
10. Wash your hands thoroughly before leaving the lab.
Data Table
Temperature, °C
Crystal Height #1, mm
Crystal Height #1, mm
Class Data
Temp, °C
Group 1
Group 2
Group 3
Group 4
45
55
65
Data Analysis
1. Find the mean crystal height obtained by your class for each temperature reported.
2. Plot the mean crystal height in millimeters (y axis) versus the water temperature (x axis).
Questions Use full sentences, not single word answers.
1. What were the independent and dependent variables in this experiment?
2. What variables were held constant?
3. Remember that a control is a sample that responds in a known way to the experiment; often it ist
the untreated sample. Was there a control in this experiment? Explain.
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4. Why was it important to have repeat trials; in other words, why is it important to collect data from
more than one trial at a particular temperature?
5. Succinic acid is slightly soluble in cold water. How was your crystal height related to the solubility
of succinic acid at the water bath temperature and at 0°C?
6. Given the pooled class data, did you have enough points to make a reliable solubility curve for
succinic acid? Would the curve be good enough to make useful predictions about succinic acid
solubility at temperatures not investigated in this activity? Explain your answer.
7. What procedures in this activity could lead to errors?
8. Using your knowledge of solubility propose a different procedure for gathering data to construct a
solubility curve. [Hint: what is a simpler, but more tedious way to determine how much salt
dissolves in water at various temperatures?]
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