Objective: To demonstrate a fermentation process, isolate the ethanol produced by fractional distillation, determine the composition of the ethanol solution recovered, and make stoichiometric and yield calculations.
Weigh out 20.0 g of sucrose and place it into a 250-mL Erlenmeyer flask. Add 100 mL of water and gently shake until all the sucrose has dissolved. To this solution add 0.60 g of dipotassium hydrogen phosphate (K), 1.8 g of sodium phosphate hydrate (Na3PO412HO) and 2.0 g of dried baker's yeast. Vigorously shake the contents to mix them thoroughly. The Erlenmeyer flask is fitted with a one-hole rubber stopper containing a short piece of glass tubing. Latex tubing (8 -12 in.) is attached to the glass tubing. An overhand knot is loosely tied in the tubing. The low part of the loop is filled with just enough water so that the passage is blocked, but gas from the fermenting chamber will be able to push the water out of the way and escape (brewers call this an airlock). This setup excludes air (and oxygen) from the system (which allows anaerobic oxidation) and prevents further oxidation (by aerobic oxidation) of the ethanol to acetic acid. Label the fermentation setup with your name and place the flask in the incubator chamber
Isolation by Fractional Distillation
Do not shake the flask; avoid disturbing the sediment on the bottom! Get your flask from the incubator bath or chamber. Carefully remove the rubber stopper from the 250-mL Erlenmeyer flask. Prepare a vacuum filtration assembly using two 250-mL side-arm filter flasks, a 5.5-cm Buchner funnel (with a Filtervac or neoprene adapter), and two lengths (each 12 in.) of vacuum tubing. [N.B. We use the second flask so between the aspirator and our filter flask so that the filtrate will not become contaminated if tap water is pulled back through the hose.] Place a piece of filter paper into the Buchner funnel so