OxfordAQA International GCSE Chemistry: Organic compounds: their structure and reactions (9202) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions are for OxfordAQA International GCSE Chemistry (9202) and are based on the OxfordAQA International GCSE Chemistry (9202) specification, Version 6.2, for exams May/June 2018 onwards. Its scope is section 3.10.3: 3.10.3.1 Alcohols, 3.10.3.2 Carboxylic acids and 3.10.3.3 Esters. Data for calculations: Ar values H = 1, C = 12, O = 16, Na = 23, K = 39, Ca = 40; molar gas volume 24 dm³ (room temperature and pressure).

Related pages: full guide to alcohols, acids and esters · condensed notes · 9202 chemistry hub · topic checklist · free diagnostics

Questions

1. Six organic compounds are listed.

Letter	Formula
A	CH₃CH₂CH₂OH
B	HCOOH
C	CH₃COOCH₂CH₃
D	C₄H₉OH
E	CH₃CH₂COOH
F	CH₃OH

(a) Give the letters of all the alcohols. [2] (b) Give the letter of the ester. [1] (c) Name compound E. [1]

2. A student investigates methanol.

(a) She adds methanol to water and then adds universal indicator. State the colour she sees and the pH of the solution. [2] (b) She adds a small piece of sodium to methanol. Give two observations. [2] (c) The equation is 2CH₃OH + 2Na → 2CH₃ONa + H₂. Calculate the volume of hydrogen, in cm³, formed when 0.23 g of sodium reacts with excess methanol. [3]

3. Ethanol is used as a fuel in some camping stoves.

(a) Write a balanced equation for the complete combustion of ethanol, C₂H₅OH. [2] (b) 9.2 g of ethanol burns completely. Work out the volume of CO₂ released, in dm³, under room conditions. [3] (c) State one use of alcohols other than as fuels. [1]

4. An opened bottle of wine is left in a warm kitchen for a week. The wine starts to taste sour.

(a) Name the acid that forms, and state the type of reaction that has happened to the ethanol. [2] (b) State what causes this change. [1] (c) State one other way that ethanol can be converted into the same acid. [1] (d) A student says, “Burning ethanol also turns it into this acid.” Explain why the student is wrong. [2]

5. A kettle descaler contains methanoic acid. Limescale is calcium carbonate, CaCO₃.

(a) Describe what you would see when the descaler is added to limescale, and give a test for the gas formed, with its result. [2] (b) Write a balanced equation for the reaction of methanoic acid with calcium carbonate. The salt formed is calcium methanoate, (HCOO)₂Ca. [2] (c) 1.25 g of calcium carbonate reacts with excess methanoic acid. Work out how many cm³ of CO₂ are given off under room conditions. [3]

6. A student measures the pH of two acid solutions. Both have a concentration of 0.10 mol/dm³.

Solution	pH
Nitric acid	1
Propanoic acid	3

(a) Explain why the propanoic acid solution has the higher pH. [3] (b) Write an equation to show propanoic acid ionising in water. Use the correct arrow. [2] (c) The student dilutes some nitric acid until its pH is 3. He says it is now a weak acid. Evaluate his claim. [2]

7. A student makes ethyl ethanoate from ethanol and ethanoic acid.

(a) State the name of the type of compound formed, and what must be added to the mixture for the reaction to happen. [2] (b) Write a balanced equation for the reaction using structural formulae. [2] (c) Calculate the maximum mass of ethyl ethanoate that can be made from 4.6 g of ethanol and excess ethanoic acid. [3] (d) The student obtains less than this mass. Suggest two reasons. [2]

8. You do not need to have met these compounds before.

butyl methanoate · pentanoic acid · ethyl propanoate · hexanol

(a) Which two of the compounds are esters? [2] (b) A compound has the structural formula CH₃CH₂COOCH₂CH₃. State the family it belongs to and give its functional group. [2] (c) Explain why esters are used in perfumes. [2]

9. A food chemist makes a fruit flavouring from ethanol in two steps.

Step 1: some ethanol is oxidised to compound X. Step 2: X reacts with more ethanol to make compound Y.

(a) Name compound X. [1] (b) Describe a test with potassium carbonate that shows X is an acid. Include a balanced equation for the reaction. [3] (c) Calculate the mass of potassium carbonate, K₂CO₃, that reacts exactly with 6.0 g of X. [3] (d) Name Y, state the condition needed for step 2, and give one property of Y that makes it suitable as a flavouring. [3]

10. Two colourless liquids, J and K, both have the molecular formula C₃H₆O₂.

J is CH₃CH₂COOH. K is CH₃COOCH₃.

(a) Identify which liquid is the carboxylic acid. Explain your answer using the formulae. [2] (b) Describe one chemical test to tell J and K apart. Give the result for each liquid. [3] (c) J reacts with sodium carbonate: 2CH₃CH₂COOH + Na₂CO₃ → 2CH₃CH₂COONa + H₂O + CO₂. 1.11 g of J reacts with excess sodium carbonate. Find the volume of gas released, in cm³, under room conditions. [3]

Answers

1. (a) A and F [1]; D [1]. (b) C [1] (c) Propanoic acid [1] Examiner insight: You must recognise D as an alcohol from its –OH, even though you never need to name it.

2. (a) Green [1]; pH 7 [1]. (b) Fizzing or bubbles [1]; the sodium gets smaller and disappears [1]. (c) Moles Na = 0.23 ÷ 23 = 0.010 mol [1]. Moles H₂ = 0.010 ÷ 2 = 0.0050 mol [1]. Volume = 0.0050 × 24 000 = 120 cm³ [1]. Examiner insight: The question asks for cm³; converting from dm³ is your job, and an answer of 0.12 with no unit change does not match what was asked.

3. (a) Correct formulae of all four substances [1]; C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O balanced [1]. (b) Moles ethanol = 9.2 ÷ 46 = 0.20 mol [1]. Moles CO₂ = 2 × 0.20 = 0.40 mol [1]. Volume = 0.40 × 24 = 9.6 dm³ [1]. (c) As a solvent (or ethanol in alcoholic drinks) [1]. Examiner insight: Write “0.20 mol ethanol gives 0.40 mol CO₂” so the 1 : 2 ratio in your method is visible.

4. (a) Ethanoic acid [1]; oxidation [1]. (b) Microbes (microbial action) using oxygen from the air [1]. (c) Warming it with a chemical oxidising agent, such as acidified potassium dichromate [1]. (d) Burning (complete combustion) produces carbon dioxide and water [1]; the molecule is broken down completely, whereas oxidation to ethanoic acid keeps the two-carbon chain [1]. Examiner insight: In part (a) “it goes off” or “fermentation” does not name a reaction type; the word needed is oxidation.

5. (a) Fizzing or bubbles [1]; the gas turns limewater milky (cloudy) [1]. (b) Correct formulae [1]; 2HCOOH + CaCO₃ → (HCOO)₂Ca + H₂O + CO₂ balanced [1]. (c) Moles CaCO₃ = 1.25 ÷ 100 = 0.0125 mol [1]. Ratio 1 : 1, so 0.0125 mol CO₂ [1]. Volume = 0.0125 × 24 000 = 300 cm³ [1]. Examiner insight: Two acid molecules are needed per carbonate; an equation with one HCOOH leaves hydrogen and oxygen unbalanced, so count atoms before moving on.

6. (a) Propanoic acid is a weak acid: it only partly ionises in water [1]. Nitric acid is a strong acid and ionises completely [1]. At the same concentration, propanoic acid therefore gives a lower concentration of H⁺ ions, and so a higher pH [1]. (b) CH₃CH₂COOH ⇌ CH₃CH₂COO⁻ + H⁺: correct ions [1]; reversible arrow ⇌ [1]. (c) The claim is wrong: nitric acid is still a strong acid [1]. It still ionises completely; it is now dilute, with fewer H⁺ ions per dm³, which is why its pH is higher [1]. Examiner insight: Part (a) needs the link to H⁺ concentration; stating “it is weak” and stopping there leaves the pH difference unexplained.

7. (a) An ester [1]; an acid catalyst [1]. (b) C₂H₅OH + CH₃COOH → CH₃COOC₂H₅ + H₂O: correct ester formula [1]; water as the other product, balanced [1]. (c) Moles ethanol = 4.6 ÷ 46 = 0.10 mol [1]. Ratio 1 : 1, so 0.10 mol ethyl ethanoate [1]. Mr = 88, so mass = 0.10 × 88 = 8.8 g [1]. (d) The reaction is reversible, so it does not go to completion [1]. Some ester is lost while it is being separated and purified (or some reactants take part in other reactions) [1]. Examiner insight: “Human error” is too vague for part (d); name a chemical reason such as reversibility.

8. (a) Butyl methanoate [1]; ethyl propanoate [1]. (b) Ester [1]; –COO– [1]. (c) Esters are volatile, so they evaporate easily and reach the nose [1]. They have distinctive, pleasant smells [1]. Examiner insight: “They smell nice” makes only one of the two points; add volatility, because a substance must evaporate before you can smell it.

9. (a) Ethanoic acid [1] (b) Add potassium carbonate: it fizzes and the gas turns limewater milky [1]. 2CH₃COOH + K₂CO₃ → 2CH₃COOK + H₂O + CO₂: correct formulae [1]; balanced [1]. (c) Moles ethanoic acid = 6.0 ÷ 60 = 0.10 mol [1]. Ratio 2 : 1, so moles K₂CO₃ = 0.050 mol [1]. Mr K₂CO₃ = 138, so mass = 0.050 × 138 = 6.9 g [1]. (d) Y is ethyl ethanoate [1]; an acid catalyst is needed [1]; it is volatile (or it has a distinctive smell) [1]. Examiner insight: In (c) many errors come from using a 1 : 1 ratio out of habit; read the ratio from your own balanced equation in (b).

10. (a) J is the carboxylic acid [1]. Its formula ends in –COOH, so the carboxyl carbon carries an O–H; in K the –COO– group has carbon on both sides, which makes K an ester [1]. (b) Add sodium carbonate solution (or another metal carbonate) to each [1]. J fizzes and gives carbon dioxide, which turns limewater milky [1]. K gives no fizzing [1]. (c) Mr J = 74, moles = 1.11 ÷ 74 = 0.015 mol [1]. Ratio 2 : 1, so moles CO₂ = 0.0075 mol [1]. Volume = 0.0075 × 24 000 = 180 cm³ [1]. Examiner insight: A test answer needs a result for both liquids; “J fizzes” alone does not show how you would tell K apart.

Where marks are usually lost

• Leaving out an alcohol or ester you have not met by name.
• Writing CO₂ and H₂O as the products when ethanol is oxidised by microbes or an oxidising agent.
• Using one acid molecule per carbonate, so the equation will not balance.
• Forgetting the ⇌ arrow for weak-acid ionisation, or not linking “weak” to partial ionisation.
• Missing the acid catalyst when describing how an ester forms.
• Using a 1 : 1 mole ratio when the equation shows 2 : 1, or forgetting to convert dm³ to cm³.
• Giving a test result for only one of two substances in a “tell apart” question.

Next steps

• Fix gaps fast with the condensed notes on this section.
• Go back over weak spots in the study guide.
• Sharpen mole calculations using OxfordAQA quantitative questions.
• Browse every 9202 unit from the chemistry hub, and record progress on the topic checklist.
• Take a 10-minute diagnostic, free, to find weak areas.
• Book a free trial class.

Official syllabus

OxfordAQA International GCSE Chemistry (9202) specification, Version 6.2, for exams May/June 2018 onwards, published by OxfordAQA. Questions written for: 3.10.3 Organic compounds – their structure and reactions (alcohols, carboxylic acids, esters).