Rate of Solution Demonstration - Experiment 14

Several factors can increase the rate of dissolution for a solid. In this demonstration, you will investigate some of these factors.

Materials Substitutions
3-600 mL beakers 3-1 quart jars
balance
1 stirring rod 1 spoon
3 sugar cubes (sucrose) 3-sugar cubes
1 mortar and pestle 1 cup and spoon
1 large hot plate 1 warming tray with 2 burners
1-800 mL beaker 1 sauce pan
2-400 mL beakers 2 measuring cups (or Pyrex glassware)
club soda (small bottle)
vacuum pump with bell jar attached

Procedure

  1. Into the three 600mL beakers (labeled #1, #2, #3), add the following:

    #1 300 mL of hot H2O (about 80 oC)
    #2 300 mL of cold H2O (about 20 oC)
    #3 300 mL of cold H2O (about 20 oC)

  2. Drop one cube of sugar into beakers #1 and #2.
  3. Use a mortar and pestle or the back of a spoon to crush a sugar cube.
  4. Drop the crushed sugar into beaker #3.
  5. Using the stirring rod, stir the contents of beaker #2, leaving beakers #1 and #3 unstirred.
  6. Observe what happens. Which method increased the rate at which sugar dissolved most? Record your data below. Draw some conclusions based on your observations.

Data and Observations
Rate of dissolution for sugar cubes in water – first, second, and third

Beaker Contents Order of dissolving
#1 300 mL of hot H2O (about 80 oC)
#2 300 mL of cold H2O (about 20oC)
#3 300 mL of cold H2O (about 20oC)

Questions

  1. How does crushing the solute (sugar) increase the rate of solution?
  2. Suppose you had a cube (6 sides) that measured 20 cm x 20 cm on each face. How much surface area would be exposed to the solvent?
  3. What would the surface area be if the same cube was crushed into 8 cubes with each face measuring 10 cm x 10 cm?
  4. How much area would be exposed if the cubes were crushed further into 8,000 cubes with each face measuring 1 cm x 1 cm?
  5. Why does stirring aid the solution process?
  6. What was the effect of increasing the temperature of the water? Why?

Extensions

  1. Carefully open the small bottle of club soda. Do not shake the bottle of club soda prior to opening it. Pour equal amounts into the two 400-mL beakers or measuring cups. Quickly, take the mass of each beaker and record these masses on the data table.
  2. Place one beaker of soda on the hot plate. As the soda heats, what do you observe? Take the second beaker of soda and place it under the bell jar of the vacuum pump. Turn the vacuum pump on. What happens? Is the solution boiling? When the bubbling stops, remove the beaker from the hot plate. Let it cool to room temperature for approximately 5-10 minutes and then reweigh it. Remove the beaker from the bell jar and weigh it. Record the masses below. What was the change in mass?

    a. Mass of soda in vacuum pump:
    before________g after___________g Difference___________g

    b. Mass of soda from hot plate:
    before________g after___________g Difference___________g

  3. What do these differences in mass tell you about the solubility of a gas in a liquid? Why should soft drinks be kept in the refrigerator?
    If you shake a bottle of soda before you open it, what will happen? Why?

Teacher’s Notes
Prior to step 1, you may wish to divide the class into groups of 3 students, with each student responsible for one of the three beakers.

The greater the surface area of the solute, the faster the rate of dissolution of the solute. Crushing increases the amount of surface area exposed to the solvent.

1 face (20 cm x 20 cm) = 400 cm 2
1 face (10 cm x 10 cm) = 100 cm 2
1 face (1 cm x 1 cm)= 1 cm 2
1 cube (400 cm 2 x 6 faces) = 2400 cm 2
8 cubes 8(100 cm 2 x 6 faces)=4800 cm2
1 cube (1 cm 2 x 6)=6 cm 2
8000 cubes=48,000 cm 2