Temperature and Solubility

Introduction

In this experiment you will see how the solubility of a solid changes as the temperature changes. Rather than determine the actual mass of the material dissolved at various temperatures you will use the volume of solid that was dissolved as an indication of the mass of solid that was dissolved.

To find how much solid is dissolved at various temperatures you will allow a hot saturated solution to cool and at specified temperatures remove a small sample with a disposable pipet and fill one well of a 12-well strip. Upon cooling excess solid will appear. The height of this solid in your well will be an indication of how much solid was dissolved at the sampled temperature.

After you complete this Exploration, you will be able to:

1. Find out how much solid is dissolved in a sample of saturated solution at a certain temperature.
2. Prepare and read a solubility graph.

Go to Top

1. Several baths will be set up in the laboratory (10°C; 25°C; 40°C; 55°C; 70°C; and 85°C). Each will be labeled and will contain a large test tube filled with a saturated solution of KClO₃. (The amount of KClO₃ dissolved in the liquid in each tube is a function of the temperature of the bath. For KClO₃, the higher the temperature, the more KClO₃ is dissolved.)

   Bath temperature °C:	10	25	40	55	70	85
   Well number	1	2	3	4	5	6

2. Select a bath. Place a Beral pipet in the tube, and alternately fill and empty it with squeezing several times. Repeat this squeezing over a minute or so to permit the liquid and the pipet to reach thermal equilibrium. Use the table to identify the appropriate well to fill. Fill the pipet about 1/3rd full with solution. Quickly fill the appropriate well of a 12-well strip with the solution. Return unused solution back to the test tube in the bath. Check the temperature of the bath. Record the temperature.
3. Repeat the procedure for each bath available.
4. When all the samples have been obtained place the 12-well strip in a shallow pan with a shallow level of ice water. After the strip has been sitting 2 minutes use a toothpick to gently stir each well. Allow the strip to set another 3 to 5 minutes and remove the strip from the cold water. Rapidly measure and record the height of the solid in each well to the nearest 0.5 mm. (Alternately, arbitrarily assign a value from 0 to 10 the the apparent height of solid in the strip with 0 = no solid and 10 = well filled with solid.)
5. Clean the solid from the strips by placing the strip in warm water, stirring each well with a toothpick. Rinse the wells with distilled water and shake all the water from the wells. Return your 12-well strip to the location specified by your instructor.
   

Go to Top

1. What happens to the solubility of potassium chlorate in water as the temperature is raised?
2. Suppose you heated your sample to 90 °C and all the solid dissolved leaving a clear solution. Would a sample of this clear solution be saturated and thus be suitable for an accurate measure of the solubility at 90 °C? Explain your answer.
3. What indicated that the solution at any given temperature was saturated?
4. Which of the solutions in the 12-well strip would have been saturated after cooling?
5. Most solids that dissolve in water behave like potassium chlorate, although the amount that dissolves will be different. Try to predict how the solubility of gases will change as the temperature is raised. Hint, think about what happens as an opened container of carbonated beverage warms.
6. Use the following graph to answer this question, how many grams of the solid will dissolve in 100 mL of water at (A) 40 °C? (B) 75 °C?
   

Go to Top

Make a graph of your own results using the temperature on the x-axis and the height of solid on the y-axis. Draw a smooth line to indicate the pattern formed. Is the line straight or curved?

Go to Top

Safety

Go to Top

1. The solubility of KClO₃ increases as the temperature increases.
2. The solution may be saturated, but it likely is less than saturated. Only when some solid remains undissolved are you sure it is saturated.
3. The presence of undissolved solid suggests that the solution is saturated.
4. All of the solutions in the 12-well strip are saturated when cooling to ice temperature since all start at above ice temperature.
5. Gases become less soluble as the temperature is raised.
6. From the graph, 25 g KClO₃ dissolve at 40 °C, and 65 g KClO₃ dissolve at 75 °C.
   

Go to Top

Sample Data:

Go to Top

• Prepare six large sized test tubes containing potassium chlorate about half full then add distilled water to a depth 5-6 centimeters higher. Heat these in large baths set to the indicated temperatures. Maintaining exact temperatures will be a problem, and using large baths and hot plates will help. Try to set the temperatures of the baths about 15-20 °C apart. When many students are in the class, use 2 or 3 test tubes per bath.
• Instruct the students to follow the pipet filling procedure so as to insure a saturated solution. Potassium chloride may be used in place of potassium chlorate, but smaller volumes of solid are produced. Other solids are certainly possible.
• At the higher temperatures pre-warming the pipets with hot water will keep solid from crystallizing in the barrel of the pipet. Make sure the students expel all the water out before drawing a sample.
• Stirring during the cooling will help settle the crystals and avoid any voids in the wells.
• You can stopper the tubes of saturated potassium chlorate and use them again in future years. You may need to add more water and solid to have adequate amounts of each.

Go to Top

• 12-well strips
• Beral pipets
• 4 hot plates
• 4 400-mL beakers
• 4 25- x 200-mm test tubes
• 250 g KClO₃
• 6 thermometers
• distilled water
• mm scale rulers
• toothpicks
• ice

Go to Top

The original version of this lesson was developed by:

Randy Emry
Southeast HS
2930 S. 37th
Lincoln, NE, 68506

Leonard Allgood
Papillion LaVista HS
402 Centennial Rd
Papillion, NE, 68406

Go to Top