Fractional Distillation of a Carbonated Soft Drink
Separating and purifying the components of mixtures is a major challenge for the chemical industry. One way it meets that challenge is by using fractional distillation. In this activity, students learn about fractional distillation by using it to separate the components of a carbonated soft drink by differences in boiling point.
Materials needed (per lab group)
- Graduated Cylinder, 100 mL
- Tygon®, Rubber, or Aquarium Tubing, 45 cm
- Utility Clamp
- Erlenmeyer Flask, 250 mL
- 2-Hole Rubber Stopper, #6
- Glass Tubing, 5 mm, 6 to 8 cm long
- Ring Stand, Iron Ring, and Wire Gauze
- Laboratory Thermometer or Temperature Probe
- 3 Test Tubes
- Test Tube Rack
- Beaker, 400 mL
- Bunsen Burner or Hot Plate
- Glass Marker
Central materials station (shared by all groups)
- Dropping Bottle of Bromthymol Blue
- Cherry Cola (or any other dark fruit-flavored carbonated soft drink)
- Lubricant (liquid soap or glycerin)
- Container of Tap Water (250 to 400 mL, pH 7 or greater)
- Boiling Chips
A solution is a homogenous mixture consisting of one phase with all components evenly distributed. A frequent task for industrial chemists is the separation of components from a mixture. This separation is often done by differences in boiling point for each component. Crude oil is separated this way. As each component in the oil reaches its boiling point, it changes into a vapor, which is then cooled and condensed back into a pure liquid. This boiling and condensing is called fractional distillation because each component separated by distillation is called a fraction.
This activity provides students with a good simulation of crude oil distillation by substituting a dark fruit-flavored carbonated soft drink, such as cherry cola or grape soda, for crude oil. The 3 main ingredients to be separated are carbon dioxide gas, flavoring, and water (in that order). All other ingredients are left behind in the flask, including high fructose syrup; coloring; leftover water; and the preservative, phosphoric acid.
- Make sure students wear gloves during the activity and use glycerin or liquid soap to lubricate the tips of the glass tubing and laboratory thermometer before inserting them into the 2-hole rubber stopper.
- Make sure students secure loose hair and clothing and use caution around the Bunsen burner or hot plate; remind them to allow the apparatus to cool to room temperature before disassembling it.
- Make sure the delivery tube from the rubber stopper to the test tube is free of kinks that would restrict the flow of gases from the distillation flask.
Tap water with 5 drops of bromthymol blue indicator is used for the 10 mL of water in tube #1. The water should be blue (slightly alkaline for municipal water) to green (pH 7) for well water. If it is yellow (pH <7), add a tiny amount of baking soda to make it a slightly alkaline blue. As CO2 bubbles from the heated soft drink into the 10 mL of water, the water changes to yellow or greenish yellow—indicating the presence of CO2 forming acidic carbonated water.
- Secure loose hair and clothing. Put on gloves.
- Lubricate one end of the 5 mm diameter glass tubing with liquid soap or glycerin.
- Hold the tubing close to the lubricated end and insert it into one hole of the 2-hole rubber stopper.
- Lubricate the bulb end of a laboratory thermometer or the end of a temperature probe and insert it into the other hole.
- Label 3 test tubes “1,” “2,” and “3.”
- Put tube #1 in the test tube rack. Fill it with 10 mL of tap water and 5 drops of bromthymol blue.
- Add 20 mL of tap water to tubes #2 and #3 and use a glass marker to mark the liquid level on each. Empty the test tubes and place them in the test tube rack.
- Fill a 400-mL beaker half full of ice and add water until the beaker is 3/4 full.
- Assemble the apparatus as shown in Fig. 1.
- Add 75 mL of soft drink and 2 boiling chips to a 250-mL Erlenmeyer flask.
- Connect Tygon®, rubber, or aquarium tubing to the glass tubing in the rubber stopper.
- Insert stopper assembly into the mouth of the flask. Keep the thermometer above the liquid inside the flask.
- Put the end of the tubing into tube #1.
Figure 1 Initial setup.
- Slowly heat the flask and watch gas bubble into the test tube. If the indicator turns yellow, then acidic carbonated water is present, which is a positive test for CO2 gas.
- While still heating the soft drink, remove the tubing from tube #1 and place it in tube #2.
- Place tube #2 with tubing in an ice bath. See Fig. 2.
Figure 2 Distillation.
- Heat the flask to boiling. Note that the boiling temperature remains constant at around 100º C. Collect the condensed distillate in tube #2 up to the 20-mL mark.
- Remove the tubing and place it in tube #3. Remove tube #2 from the ice water bath and place it in the test tube rack.
- Place tube #3 in the ice water bath and collect another 20 mL of distillate.
- Quit heating when 20 mL are collected in tube #3. Place tube #3 in the test tube rack.
- Allow the apparatus to cool to room temperature before disassembling.
- Did the water in tube #1 turn yellow? If so, what does this prove?
- Smell tube #2 by wafting toward your nose. Describe the smell.
- Smell tube #3 by wafting toward your nose. Describe the smell as compared to tube #2.
- Describe what is left in the flask.
- Describe the order in which the fractions of flavoring, water, and CO2 were removed from the soft drink solution.
- What is the major component in tubes #2 and #3?
Students can calculate the density of the soft drink solution before distillation by weighing 10.0 mL of soft drink to the nearest 0.01g on a balance. They then divide the mass by the volume to get the density of the solution in g/mL. Students compare this density to the density of 10.0 mL of the solution left in the flask at the end of the experiment. The density of the solution left in the flask should be higher due to a larger amount of sugar per given amount of leftover water. Also, students can measure 10.0 mL of the liquid in tube #3, weigh it, and calculate the density. The answer should be 1.0 g/mL, which is the density of water.