Chemistry • Year 12 • Module 7 • Lesson 10
Production of Alcohols: Hydration, Substitution & Fermentation
Lock in the key vocabulary, balanced equations, and conditions for all three methods of alcohol production before moving to higher-order application.
1. Label the alcohol-production pathway diagram
The diagram below shows three industrial/biological routes to produce an alcohol from different starting materials. Write the missing labels into boxes A–H. Each label is drawn from the lesson's Key Terms or equation conditions. 8 marks
- A — catalyst used in alkene hydration _______________________
- B — temperature used in alkene hydration _______________________
- C — arrow notation for the hydration equation _______________________
- D — type of NaOH used to give substitution (not elimination) _______________________
- E — equipment used in haloalkane substitution to prevent volatile loss _______________________
- F — arrow notation for haloalkane substitution _______________________
- G — biological catalyst used in fermentation _______________________
- H — atmospheric condition required for fermentation _______________________
2. Term–definition match
The ten definitions below are shuffled. In the right-hand column write the matching term from this list: hydration of alkenes, nucleophilic substitution, fermentation, fractional distillation, zymase, reflux, single-pass conversion, Le Chatelier’s Principle, rate-yield compromise, anaerobic. 10 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 2.1 | Addition of water (steam) across a C=C double bond using an acid catalyst to produce an alcohol. | |
| 2.2 | Conditions that exclude oxygen; required for yeast to produce ethanol rather than CO&sub2; and water. | |
| 2.3 | The enzyme produced by yeast cells that catalyses the conversion of glucose to ethanol and CO&sub2;. | |
| 2.4 | A reaction where OH¹¯ replaces the halogen on a haloalkane; requires aqueous NaOH. | |
| 2.5 | The enzymatic conversion of glucose to ethanol and carbon dioxide by yeast under anaerobic conditions. | |
| 2.6 | A heating technique where volatile vapours are condensed by a water-cooled condenser and returned to the reaction flask. | |
| 2.7 | The separation technique used to purify dilute ethanol from a fermentation mixture, exploiting differences in boiling point. | |
| 2.8 | The fraction of reactants converted to product in one pass through the reactor (~5% for industrial ethanol hydration). | |
| 2.9 | The principle that a system at equilibrium will shift to oppose a change in conditions such as pressure or temperature. | |
| 2.10 | The choice of a temperature that is not optimal for equilibrium yield but gives an acceptable reaction rate for industrial production. |
3. True or false — with correction
For each statement, circle T or F. If the statement is false, write the corrected version on the line below. 8 marks (1 T/F, 1 correction where needed)
3.1 High temperature is used in alkene hydration to increase the equilibrium yield of ethanol. T / F
3.2 The balanced fermentation equation is C&sub6;H&sub1;&sub2;O&sub6; → 2C&sub2;H&sub5;OH + 2CO&sub2;. T / F
3.3 Alcoholic NaOH gives nucleophilic substitution with a haloalkane to produce an alcohol. T / F
3.4 Fermentation typically stops when ethanol concentration reaches approximately 15% because it becomes toxic to the yeast. T / F
4. Fill the blank — alcohol production conditions
Complete the paragraph below by writing one term or phrase in each blank. Use the word bank provided. 10 marks
The industrial hydration of ethene to ethanol uses _______________(1) as a heterogeneous catalyst at a temperature of approximately _______________(2) and a pressure of _______________(3). The reaction is an _______________(4), meaning both the forward and reverse reactions occur simultaneously. In contrast, the nucleophilic substitution of a haloalkane with aqueous NaOH is carried out under _______________(5) conditions to prevent volatile reactants escaping, producing an alcohol and the salt _______________(6). Fermentation of glucose requires the enzyme _______________(7) produced by yeast, an optimal temperature of _______________(8), and _______________(9) conditions (no oxygen). Fermentation stops automatically when ethanol concentration reaches about _______________(10).
5. Function recall
Answer each question in 1–2 sentences using precise terms from the lesson. 8 marks (2 each)
5.1 What is the function of the reflux condenser in the haloalkane substitution reaction?
5.2 What is the function of high pressure (~65 atm) in the industrial hydration of ethene?
5.3 Why must NaOH be aqueous (dissolved in water) rather than dissolved in ethanol for nucleophilic substitution?
5.4 What is the purpose of recycling unreacted ethene in the industrial hydration process?
Q1 — Labelled diagram
A: H&sub3;PO&sub4; (phosphoric acid, absorbed on silica — heterogeneous catalyst). B: ~300°C. C: ⇌ (equilibrium/reversible arrow). D: aqueous NaOH (dissolved in water). E: reflux condenser (round-bottom flask + water-cooled condenser). F: → (single/one-way arrow — goes to completion). G: yeast / zymase enzyme. H: anaerobic (no oxygen / air excluded).
Q2 — Term–definition matches
2.1 hydration of alkenes • 2.2 anaerobic • 2.3 zymase • 2.4 nucleophilic substitution • 2.5 fermentation • 2.6 reflux • 2.7 fractional distillation • 2.8 single-pass conversion • 2.9 Le Chatelier’s Principle • 2.10 rate-yield compromise.
Q3 — True / false with correction
3.1 False. Correction: High temperature is used as a rate compromise, not to increase yield. The hydration reaction is exothermic, so by Le Chatelier’s Principle, higher temperature shifts the equilibrium left (decreasing ethanol yield). 300°C is chosen to give an acceptable reaction rate, not maximum yield.
3.2 True.
3.3 False. Correction: Alcoholic NaOH (NaOH dissolved in ethanol) gives elimination to produce an alkene, not substitution. Aqueous NaOH (dissolved in water) gives nucleophilic substitution to produce an alcohol.
3.4 True.
Q4 — Cloze answers
(1) H&sub3;PO&sub4; • (2) ~300°C • (3) ~65 atm • (4) equilibrium • (5) reflux • (6) NaX • (7) zymase • (8) 35°C • (9) anaerobic • (10) ~15%.
Q5.1 — Function of the reflux condenser
The reflux condenser cools volatile vapours (haloalkane and/or alcohol) that rise from the heated flask back into liquid, which drips back into the flask. This prevents loss of volatile reactants and products, keeping them in contact in the flask and improving yield.
Q5.2 — Function of high pressure
The hydration equation CH&sub2;=CH&sub2; + H&sub2;O ⇌ CH&sub3;CH&sub2;OH has 2 moles of gas on the left and 0 on the right (ethanol condenses). By Le Chatelier’s Principle, high pressure (~65 atm) shifts the equilibrium to the side with fewer moles of gas (right side / products), increasing ethanol yield.
Q5.3 — Why aqueous NaOH
The solvent determines the reaction pathway. Aqueous NaOH provides OH¹¯ as a nucleophile in a polar protic solvent, favouring substitution (replacing the halogen with —OH to give an alcohol). Alcoholic NaOH provides a strong base in a less polar environment, favouring elimination (removing HX to give an alkene). Always state “aqueous” in exam answers.
Q5.4 — Purpose of recycling ethene
Single-pass conversion is only ~5% — most ethene exits the reactor unreacted. Separating and recycling unreacted ethene back to the reactor inlet allows it to pass through again and again. This continuous recycling achieves high overall yield (approaching complete conversion) despite the low equilibrium conversion per pass.