Ethanol is used as a fuel for cars. It can be made by fermenting glucose from sugar cane.
C6H12O6(aq)→2C2H5OH(aq)+2CO2(g)\mathrm{C_{6}H_{12}O_{6}(aq)} \rightarrow \mathrm{2C_{2}H_{5}OH(aq)} + \mathrm{2CO_{2}(g)}C6H12O6(aq)→2C2H5OH(aq)+2CO2(g)
Relative formula masses: C6H12O6=180,C2H5OH=46,CO2=44\mathrm{C_{6}H_{12}O_{6}} = 180, \mathrm{C_{2}H_{5}OH} = 46, \mathrm{CO_{2}} = 44C6H12O6=180,C2H5OH=46,CO2=44
Calculate the maximum mass of ethanol that can be made from 450 g of glucose.
In a trial, 161 g of ethanol was obtained from 450 g of glucose. Calculate the percentage yield.
Calculate the atom economy for making ethanol by fermentation. Give your answer to three significant figures.
Ethanol can also be made by reacting ethene with steam.
C2H4(g)+H2O(g)→C2H5OH(g)\mathrm{C_{2}H_{4}(g)} + \mathrm{H_{2}O(g)} \rightarrow \mathrm{C_{2}H_{5}OH(g)}C2H4(g)+H2O(g)→C2H5OH(g)
The table gives information about the two methods.
| Feature | Fermentation of glucose | Ethene + steam |
|---|---|---|
| Source of raw material | sugar cane (renewable) | crude oil (non-renewable) |
| Temperature / °C | 30 | 300 |
| Pressure / atm | 1 | 60 |
| Rate of reaction | slow | fast |
| Type of process | batch | continuous |
| Purity of ethanol produced | about 15% in water | about 96% |
| Atom economy / % | your answer to (c) | 100 |
Evaluate the two methods for making ethanol for use as a car fuel. Use the information in the table and your knowledge.
43 exam-style questions on Edexcel GCSE Chemistry 10.4 Alcohols and carboxylic acids, covering 10.4.1 Alcohols and the -OH functional group, 10.4.2 Carboxylic acids and the -COOH functional group, 10.4.3 Oxidation of alcohols and homologous series, and 10.4.4 Fermentation and fractional distillation of ethanol. Each one has a worked solution and a mark scheme showing where the marks go.