Carboxylic acids
Cambridge A-Level Chemistry (9701) · Unit 33: Carboxylic acids and derivatives (A Level) · 8 flashcards
Carboxylic acids is topic 33.1 in the Cambridge A-Level Chemistry (9701) syllabus , positioned in Unit 33 — Carboxylic acids and derivatives (A Level) , alongside Esters and Acyl chlorides. In one line: Benzoic acid is produced by the oxidation of alkylbenzenes, such as toluene, using hot alkaline potassium manganate(VII) (KMnO₄) as the oxidising agent. The alkyl group is oxidised to the carboxyl group.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 8 flashcards — 3 definitions, 4 key concepts and 1 calculation — covering the precise wording mark schemes reward. Use the 3 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
How is benzoic acid commonly produced in the lab
Benzoic acid is produced by the oxidation of alkylbenzenes, such as toluene, using hot alkaline potassium manganate(VII) (KMnO₄) as the oxidising agent. The alkyl group is oxidised to the carboxyl group.
What the Cambridge 9701 syllabus says
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- recall the reaction by which benzoic acid can be produced:
- describe the reaction of carboxylic acids with PCl ₃ and heat, PCl ₅ or SOCl ₂ to form acyl chlorides
- recognise that some carboxylic acids can be further oxidised: (a) the oxidation of methanoic acid, HCOOH, with Fehling’s reagent or Tollens’ reagent or acidified KMnO₄ or acidified K₂Cr₂O₇ to carbon dioxide and water (b) the oxidation of ethanedioic acid, HOOCCOOH, with warm acidified KMnO₄ to carbon dioxide
- describe and explain the relative acidities of carboxylic acids, phenols and alcohols
- describe and explain the relative acidities of chlorine-substituted carboxylic acids
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9701 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Carboxylic acids
- › Check the question conditions carefully; use 22.4 dm³ per mole for calculations involving gas at s.t.p.
How is benzoic acid commonly produced in the lab?
Benzoic acid is produced by the oxidation of alkylbenzenes, such as toluene, using hot alkaline potassium manganate(VII) (KMnO₄) as the oxidising agent. The alkyl group is oxidised to the carboxyl group.
What products are formed when a carboxylic acid reacts with PCl₃ and heat?
A carboxylic acid reacts with PCl₃ and heat to form an acyl chloride, phosphorus acid (H₃PO₃), and HCl.
Write the balanced equation for the oxidation of methanoic acid (HCOOH) with acidified potassium permanganate (KMnO₄).
2KMnO₄ + 5HCOOH + 3H₂SO₄ → K₂SO₄ + 2MnSO₄ + 5CO₂ + 8H₂O. Methanoic acid is oxidised to carbon dioxide and water.
Describe the reaction of ethanedioic acid (HOOCCOOH) with warm acidified KMnO₄.
Ethanedioic acid is oxidised to carbon dioxide by warm, acidified potassium permanganate (KMnO₄). The purple colour of the KMnO₄ decolourises as MnO₄⁻ is reduced to Mn²⁺.
Explain the relative acidities of carboxylic acids, phenols, and alcohols.
Carboxylic acids are generally more acidic than phenols, which are more acidic than alcohols. This is because the negative charge on the carboxylate ion (RCOO⁻) is delocalised over two oxygen atoms, making it more stable than the phenoxide ion (delocalised over the benzene ring). Alkoxide ions are the least stable.
How does the presence of chlorine substituents affect the acidity of carboxylic acids? Explain why.
Chlorine substituents increase the acidity of carboxylic acids. This is because chlorine is electron-withdrawing, which stabilises the carboxylate anion by dispersing the negative charge, making the acid more likely to donate a proton.
Write the general equation for the reaction of a carboxylic acid with thionyl chloride (SOCl₂).
RCOOH + SOCl₂ → RCOCl + SO₂ + HCl. This reaction produces an acyl chloride, sulfur dioxide, and hydrogen chloride gas.
What is the product formed when ethanoic acid reacts with phosphorus pentachloride (PCl₅)?
The reaction of ethanoic acid (CH₃COOH) with phosphorus pentachloride (PCl₅) forms ethanoyl chloride (CH₃COCl), phosphorus oxychloride (POCl₃), and hydrochloric acid (HCl).
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All Chemistry FlashcardsMore topics in Unit 33 — Carboxylic acids and derivatives (A Level)
Carboxylic acids sits alongside these A-Level Chemistry decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
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