When grains, tubers, and fruits ferment, the carbohydrates in them are converted by a series of reactions to ethanol, CH3CH2OH. Various enzymes contained in yeast speed up the reaction involved. Prior to this experiment, your teacher mixed some yeast with sugar and warm water. This mixture was added to a large bottle containing 2500 mL of warm water and 500 mL of molasses. This has been quietly fermenting for several days.
In this experiment, you will distill the ethanol from the fermentation mixture, and then you will determine some of the properties of the purified ethanol.
Purpose: To prepare ethanol and identify some if its components.
Apparatus: Use the diagram below to help set up your equipment.
| 250 mL distillation flask or Florence flask | Rings stands |
| clamps | water condenser |
| condenser clamp | one-hole rubber stopper for condenser |
| bent glass tubing (approximately 60o) | 2 pieces of rubber tubing |
| two-hole rubber stopper for flask | wire gauze |
| evaporating dishes | iron ring |
| large watch glass | Bunsen burner |
Materials: Molasses and yeast mixture, wooden splints, boiling chips
Procedure:
| 1. | In a 250 mL flask place 150 mL of the fermented liquid and several boiling chips. Assemble the apparatus as shown above. Check that all your connections are tight. When satisfied have the teacher check them as well. |
| 2. | Heat the solution with a bunsen burner and collect the distillate in a 50 mL Erlenmeyer flask. As the temperature starts to rise record the temperature every 30 seconds until heating is discontinued. |
| 3. | Record the temperature when the first drop of distillate appears. Stop heating the mixture 10 degrees after it starts to rise rapidly again once it has plateaued. |
| 4. | Place some of the distillate from the Erlenmeyer into an evaporating dish. What is the odour of this portion? Bring a burning splint close to the surface of this fluid. Does it ignite? If it does cover the evaporating dish with a watch glass immediately. |
| 5. | Empty the distillation flask. Put the distillate back into the flask and distill it again with a fresh boiling chip. Again record the temperature every 30 seconds once the temperature starts to rise. Collect a 10 mL portion of distillate. |
Calculations: Prepare two temperature versus time graphs. One for the first distillation, one for the second distillation. Compare the two graphs. Are there any differences?
Questions:
1. What are the physical properties of the ethanol
that you were able to observe?
2. What are the temperatures at the beginning and end of each distillation?
3. What is the odour of the second distillate?
4. Does this portion ignite when tested with a burning splint?
5. What is the chemical equation for the preparation of ethanol from sucrose , C12H22O11?
6. What is the chemical equation for the combustion of ethanol?
7. What are some of the most important industrial
uses for ethanol?