IGCSE Chemistry: Alcohols and Carboxylic Acids — Practice Questions

These are original questions written for Marlbridge, in the style and at the standard of the examination. They are not reproduced past-paper questions — examination boards hold copyright in their own papers. Use these alongside the official past papers available free from your board.

Related: Alcohols and Carboxylic Acids study guide, which covers Topic 11.6 Alcohols and 11.7 Carboxylic acids for Cambridge IGCSE 0620 and O Level 5070.

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Questions

1. State the two industrial methods used to manufacture ethanol. [2]

2. Fermentation must take place in the absence of oxygen.

(a) State the name given to a reaction that occurs without oxygen. [1] (b) Explain what happens if oxygen is not excluded during fermentation. [1]

3. Compare fermentation and the catalytic addition of steam to ethene as methods of manufacturing ethanol, giving one advantage of each method. [2]

4. Ethanoic acid reacts with magnesium carbonate.

(a) Name the three products of this reaction. [3] (b) Write a word equation for this reaction. [1]

5. Describe two different ways in which ethanoic acid can be made from ethanol. [2]

6. Ethanoic acid reacts with ethanol in the presence of an acid catalyst.

(a) Name the type of reaction taking place. [1] (b) Name the organic product formed. [1] (c) State the other product of this reaction. [1]

7. Explain why fermentation is often described as producing a “dilute, impure” product, while the ethene route produces a pure, continuous stream. [2]

8. State two uses of ethanol, and write a balanced symbol equation for its complete combustion. [3]

9. A student adds equal-concentration solutions of ethanoic acid and hydrochloric acid, separately, to identical pieces of magnesium ribbon.

(a) State which acid reacts more vigorously. [1] (b) Explain this difference in terms of the strength of the two acids. [2]

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Answers

1. Fermentation of aqueous glucose using yeast [1]; catalytic addition of steam to ethene, using an acid catalyst [1].

2. (a) Anaerobic [1]. (b) The yeast respires aerobically instead, and no ethanol accumulates [1].

3. Fermentation: uses a renewable raw material (glucose from plants) [1]. Steam + ethene: is much faster and produces a pure, continuous product [1]. Any other valid advantage for either method (e.g. fermentation needs only mild conditions; the ethene route doesn’t need further purification) should be credited.

4. (a) Magnesium ethanoate, water and carbon dioxide [3]. (b) ethanoic acid + magnesium carbonate → magnesium ethanoate + water + carbon dioxide [1].

5. Oxidation with acidified aqueous potassium manganate(VII) [1]; bacterial oxidation (as in vinegar production) [1].

6. (a) Esterification (condensation) [1]. (b) Ethyl ethanoate [1]. (c) Water [1].

7. Fermentation produces ethanol mixed with water and yeast/other by-products, so it needs further distillation to concentrate it, and the batch process is inherently less pure [1]; the ethene route is a continuous industrial process using a pure gaseous reactant, so it produces ethanol at high purity directly [1].

8. As a solvent, since it can dissolve substances that water cannot [1], and as a fuel, since it burns exothermically [1]. C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O [1].

9. (a) The hydrochloric acid reacts more vigorously (faster bubbling/effervescence) [1]. (b) Hydrochloric acid is a strong acid, which fully ionises in water to give a high concentration of H⁺ ions [1]; ethanoic acid is a weak acid, which only partially ionises, giving a lower concentration of H⁺ ions at the same overall concentration, so it reacts more slowly [1].

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Where marks are usually lost

• Saying fermentation happens in the presence of oxygen.
• Writing the ethanol-to-ethanoic-acid oxidation as if it were combustion, rather than gaining oxygen/losing hydrogen.
• Naming the ester the wrong way round — the alcohol supplies the “-yl” part, the acid supplies the “-oate” part.
• Forgetting fermentation’s product needs further distillation before it is usable as a concentrated fuel or solvent.
• Giving “temperature” or “pressure” alone as a reaction condition for the steam–ethene route — state whether it is high or low (or the actual value), since an unqualified condition is not creditworthy.
• Confusing “weak acid” with “dilute acid” — ethanoic acid is weak (partially ionises) regardless of its concentration; a dilute solution of a strong acid still ionises fully, it just has fewer H⁺ ions overall than a concentrated one.
• Forgetting the combustion equation must balance, particularly the oxygen coefficient (3O₂ on the left, matching 2CO₂ + 3H₂O on the right).

Ethanol and ethanoic acid — the reaction network in one place

Ethanol and ethanoic acid are linked by a small, connected network worth holding in mind as a whole rather than as isolated facts: ethanol can be oxidised to ethanoic acid (by acidified KMnO₄ or by bacteria, as in vinegar production); ethanoic acid can react with an alcohol to form an ester; and ethanol itself can be made from ethene by an addition reaction — hydration. Exam questions frequently test whether a candidate can move between these related facts rather than recall any single one in isolation, for instance asking how the ethanol used in an esterification reaction could itself have been manufactured. For the full explanation of each stage of this network, including the syllabus split between Core and Supplement content, see the Alcohols and Carboxylic Acids study guide. Note that the ester-formation and ethanol-oxidation reactions are Supplement content for 0620 candidates, but are required outcomes for every O Level 5070 candidate, since 5070 has no Core/Supplement split — always check which specification you are being examined against before deciding how much of this network to prioritise in revision.