YJC_H2_CHEM_P2_Answer

2 9647 / YJC / 2014 / Preliminary Examination / Paper 2 Answer all the questions. Planning (P) 1 Fermentation is a natural process. Man applied fermentation to make products such as wine, mead, cheese and beer long before the biochemical process was understood. In the 1850s and 1860s, Louis Pasteur became the first scientist to be known to have studied fermentation when he demonstrated fermentation was caused by living cells. The fermentation of carbohydrates into alcohol can be represented as: Sugar  alcohol + carbon dioxide This reaction is catalyzed by yeast enzymes called zymases. A balanced chemical equation for this process using table sugar or sucrose is: C12H22O11 + H2O  4CH3CH2OH + 4CO2 This type of yeast fermentation can be studied through its CO 2 production. Using the information above, you are required to write a plan to determine the rate of CO 2 production in a 30–minute fermentation process. You are provided with the following materials: - 0.100 mol dm3 sucrose solution - yeast suspension - apparatus normally found in a school laboratory (a) Write a step-by-step plan on how you would carry out this experiment. Your plan should include the following: - show how the quantity of sucrose used is calculated - all essential experimental details - a diagram of your experimental set up - a table with appropriate headings to show the data you would record when carrying out your experiment Quantity of sucrose C12H22O11 ≡ 4CO2 Note volume of syringe = V 1 cm3 then V CO2 collected should be less than V1 cm3 V1 = ηCO2 = a mol 24000 ⇒ ηsucrose = ¼ a mol ∴ volume of sucrose (aq) used must be less than ¼ a x 1000 cm3 0.1 Let the volume of aq. sucrose used be V2 cm3. 2014_YJC_H2_Chem_P2_ Solution

3 9647 / YJC / 2014 / Preliminary Examination / Paper 2 Experimental details: 1. Place V 2 cm3 of sucrose (aq) and equal volume of yeast suspension into a 250 cm3 conical flask and stopper the flask. 2. Allow the mixture to incubate for 5 minutes. Note temperature of the surroundings. 3. Attach a calibrated syringe (Volume = V 1 cm3) to the flask according to the diagram: 4. As soon as the piston reaches the 0 mark on the syringe, start the stop watch. 5. Take volume readings at 2 minute intervals for 30 minutes and record the data collected in the table below. Time, t (min) Reading on syringe = Vol of CO2 (cm3) [6] 0 mark

4 9647 / YJC / 2014 / Preliminary Examination / Paper 2 Alcohol produced by this fermentation, from the aqueous solution in which the fermentation takes place is concentrated or enriched by distillation. A quantity of reaction mixture, after the fermentation process, is placed in the following set-up. (b) What is meant by distillation?