The shape of the lesson
By the end of the lesson, learners can
- Making ethanol: Learn the conditions for each route exactly; they are asked for word for word.
- Which method is better?: Extended.
- Burning and using ethanol: Explore the reactions of ethanol in the simulator, including what happens when it burns in a good supply of air.
- Fermentation: glucose, yeast, 25–35 °C, no oxygen; gives CO2 too.
- Hydration: ethene + steam, 300 °C, 6000 kPa, acid catalyst.
- Extended: renewable but slow and impure vs fast and pure but non-renewable.
- Combustion: C2H5OH + 3O2 → 2CO2 + 3H2O.
One picture every idea returns to
Alcohols contain the –OH functional group; ethanol is C2H5OH. Ethanol is made by fermentation: aqueous glucose with yeast at 25–35 °C in the absence of oxygen: C6H12O6 → 2C2H5OH + 2CO2. It is also made by the catalytic addition of steam to ethene at about 300 °C and 6000 kPa with an acid catalyst (phosphoric acid): C2H4 + H2O → C2H5OH. Extended: fermentation uses a renewable raw material and little energy but is slow and gives impure, dilute ethanol; hydration is fast, continuous and gives pure ethanol but uses non-renewable crude oil and much energy. Ethanol burns completely to carbon dioxide and water and is used as a fuel and a solvent.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Two routes to ethanol.. Ethanol can be brewed from sugar by yeast in a warm tank, or made in a chemical plant by adding steam to ethene from crude oil. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Making ethanol | Learn the conditions for each route exactly; they are asked for word for word. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Which method is better? | Extended. | Pairs |
| 21 to 30 min | Teach and check: Burning and using ethanol | Explore the reactions of ethanol in the simulator, including what happens when it burns in a good supply of air. Project tab 4 of the lab (Hydroxy compounds lab, reactions of ethanol) and let a student drive it while the class predicts. | Connect-Extend-Challenge |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 18 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Burning and using ethanol, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Connect-Extend-Challenge
After the new idea, each student writes three lines: how it connects to what they knew, how it extends their thinking, and what still challenges them. Pairs compare, then the challenges become the plenary.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Fermentation needs the absence of oxygen, but combustion of ethanol needs oxygen: do not mix them up. | The fermentation temperature is 25–35 °C, not a high temperature: heating kills (denatures the enzymes in) the yeast. In the hydration equation water is steam, and the catalyst is an acid (phosphoric acid), not yeast. |
Alcohols: worksheet
6 questions, 18 marks. Written in the style of the papers; no past paper question is reproduced.
Describe the conditions needed to make ethanol by fermentation of aqueous glucose.
Write the balanced equation for the manufacture of ethanol from ethene, and state the conditions used.
Calculate the maximum mass of ethanol that can be made by fermenting 45.0 g of glucose, C6H12O6. (Ar: C 12, H 1, O 16)
(Extended) A country has large areas of farmland but no crude oil. Explain which method of making ethanol it should use, giving two advantages and one disadvantage of that method.
Calculate the volume of carbon dioxide, at room temperature and pressure, produced when 9.2 g of ethanol burns completely. (Molar gas volume 24 dm3)
Explain why the fermentation mixture is not heated above about 35 °C, and why air is kept out.
Answer key and marking notes
- Yeast is added.
- Temperature of 25–35 °C.
- Oxygen (air) is kept out: anaerobic conditions.
- C2H4 + H2O → C2H5OH (water as steam).
- About 300 °C and 6000 kPa (60 atm).
- Acid catalyst (phosphoric acid).
- Mr glucose = 180, so moles = 45.0 ÷ 180 = 0.250 mol.
- 1 mol glucose gives 2 mol ethanol, so 0.500 mol ethanol.
- Mr ethanol = 46, so mass = 0.500 × 46 = 23.0 g.
- Fermentation, because it does not need crude oil.
- Advantage: the raw material (sugar from crops) is renewable.
- Advantage: low temperature, so low energy costs and simple equipment.
- Disadvantage: slow batch process giving impure ethanol that must be distilled (or: uses land that could grow food).
- Moles of ethanol = 9.2 ÷ 46 = 0.20 mol.
- C2H5OH + 3O2 → 2CO2 + 3H2O, so 0.40 mol CO2.
- Volume = 0.40 × 24 = 9.6 dm3.
- Above about 35 °C the enzymes in the yeast are denatured, so fermentation stops.
- With air, the yeast respires aerobically and the ethanol can be oxidised to ethanoic acid.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Which conditions are used to make ethanol by fermentation?
- Asugar solution and yeast at about 30 °C with no oxygen
- Bethene and steam at 300 °C with an acid catalyst
- Csugar solution and yeast at 100 °C in air
- Dglucose with a nickel catalyst at 150 °C
Which is the word equation for fermentation?
- Aglucose → ethanol + carbon dioxide
- Bglucose + oxygen → ethanol + water
- Cethene + steam → ethanol
- Dethanol + oxygen → carbon dioxide + water
Which is the balanced equation for the complete combustion of ethanol?
- AC2H5OH + 3O2 → 2CO2 + 3H2O
- BC2H5OH + 2O2 → 2CO2 + 3H2O
- CC2H5OH + 3O2 → 2CO2 + 2H2O
- DC2H5OH + O2 → CH3COOH + H2O
Which is a use of ethanol?
- Aas a solvent and as a fuel
- Bas a catalyst for cracking
- Cas a monomer for making poly(ethene)
- Dto make bromine water colourless as a test for alkenes
Fermentation stops when the ethanol concentration reaches about 15%. How is a more concentrated solution of ethanol obtained?
- Afractional distillation
- Bfiltration
- Cadding more yeast
- Dcracking
Which is an advantage of making ethanol by fermentation rather than by the catalytic addition of steam to ethene?
- Ait uses a renewable raw material
- Bit is a continuous process
- Cit produces pure ethanol
- Dit has a faster rate of reaction
A country has large petroleum reserves but little land for crops. Which method of making ethanol suits it best, and why?
- Aaddition of steam to ethene, because ethene is available from cracking petroleum and the process is fast and continuous
- Bfermentation, because it gives pure ethanol
- Cfermentation, because it is a continuous process
- Daddition of steam to ethene, because the raw material is renewable
1.15 g of ethanol (Mr = 46) burns completely. What volume of carbon dioxide forms at room temperature and pressure? (1 mol of gas occupies 24 dm3)
- A1.20 dm3
- B0.600 dm3
- C1.80 dm3
- D2.40 dm3
Quiz key
Yeast converts sugar (glucose) into ethanol and carbon dioxide at a warm temperature of about 25–35 °C, in the absence of oxygen. Ethene with steam is the other manufacturing method, catalytic addition. At 100 °C the yeast enzymes are denatured, and with oxygen present the yeast respires aerobically and ethanol can be oxidised. Nickel is used to add hydrogen to alkenes.
Yeast breaks glucose down into ethanol and carbon dioxide: C6H12O6 → 2C2H5OH + 2CO2. Oxygen is not a reactant because fermentation is anaerobic. Ethene + steam is the catalytic addition method. Ethanol + oxygen is the combustion of ethanol.
Ethanol has 2 C and 6 H, giving 2CO2 and 3H2O, which contain 4 + 3 = 7 O. Ethanol supplies 1 O, so 6 O (3O2) are needed. With 2O2 the left has only 5 O. 2H2O only accounts for 4 of the 6 hydrogen atoms. Forming ethanoic acid is oxidation, not combustion.
Ethanol is used as a solvent (for example in perfumes and medicines) and as a fuel. Cracking uses catalysts such as aluminium oxide. The monomer for poly(ethene) is ethene, not ethanol. Bromine water is decolourised by alkenes; ethanol is not used for that test.
Ethanol (boiling point 78 °C) and water (100 °C) are separated by fractional distillation. Filtration only removes solids such as yeast. Adding more yeast does not help, because the ethanol itself kills the yeast at high concentration. Cracking breaks large hydrocarbons and does not separate mixtures.
Fermentation uses sugar from crops, which can be regrown, so its raw material is renewable. Ethene comes from cracking petroleum, which is non-renewable. However, fermentation is a slow batch process that gives a dilute, impure solution needing distillation. The steam method is continuous, fast and gives pure ethanol, so the other three options are advantages of the ethene route.
With petroleum available and little farmland, the steam and ethene route is better: ethene comes from cracking petroleum, and the process is fast, continuous and gives a high purity product. Fermentation needs farmland for sugar crops, gives impure dilute ethanol and is a batch process. Ethene from petroleum is non-renewable, so the last reason is wrong.
Moles of ethanol = 1.15 / 46 = 0.0250 mol. Each mole gives 2 mol CO2, so 0.0500 mol CO2, and 0.0500 × 24 = 1.20 dm3. 0.600 dm3 ignores the 1 : 2 ratio. 1.80 dm3 uses the 1 : 3 ratio of water or oxygen instead of CO2. 2.40 dm3 comes from using 0.1 mol, a slip in the moles calculation.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.