AQA GCSE Chemistry 8462: Organic chemistry – 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 cover Topic 7, Organic chemistry (sections 4.7.1 to 4.7.3), of the AQA GCSE Chemistry (8462) specification, for teaching from September 2016 with exams from June 2018 (version 1.1). The topic is examined on Paper 2 at Foundation and Higher tier. Question 7(c) and Question 9 test Higher tier only content and are labelled; everything else is for both tiers. Use relative atomic masses: C = 12, H = 1, O = 16, Cl = 35.5.

Learn the content first in the study guide and the revision notes. The course hub is AQA GCSE Chemistry and the printable checklist lists every statement.

Questions

1. Here are four formulae: C4H10, C4H8, C5H12, C2H5OH. Give the two formulae that are alkanes, and name the alkane with four carbon atoms. [2]

2. Explain how crude oil is separated into fractions by fractional distillation. Refer to evaporation and condensation in your answer. [4]

3. A fuel company compares two hydrocarbons, C6H14 and C16H34.

(a) Suggest which is the better fuel for a camping stove. Give one reason based on a property that depends on molecular size. [2] (b) Write a balanced equation for the complete combustion of C6H14. [2]

4. A refinery cracks a hydrocarbon with formula C11H24.

(a) Describe, in general terms, the conditions used for steam cracking. [2] (b) Complete the equation: C11H24 → C7H16 + 2 ____ [1] (c) Describe a test to show that one product is an alkene. Give the result. [2] (d) Give two reasons why cracking is useful. [2]

5. This question is about ethene and propene.

(a) Draw the displayed formula of the product formed when ethene reacts with chlorine. [2] (b) Explain why propene tends to burn in air with a smoky flame. [1] (c) Propene reacts with hydrogen. Name the product and the catalyst used. [2]

6. A student investigates propanol, C3H7OH.

(a) Describe what the student would see when a small piece of sodium is added to propanol, and name the gas formed. [2] (b) Write a balanced equation for the complete combustion of propanol. [2] (c) Ethanol for drinks is made by fermentation. State two conditions used. [2]

7. This question is about carboxylic acids.

(a) Propanoic acid is added to sodium carbonate solution. State what is seen and name the gas formed. [2] (b) Ethanoic acid is warmed with ethanol and an acid catalyst. Name the organic product and the type of compound it is. [2] (c) (Higher tier only) A solution of ethanoic acid has a higher pH than a solution of hydrochloric acid of the same concentration. Explain why. [3]

8. Chloroethene has the structure CH2=CHCl. It forms the addition polymer poly(chloroethene).

(a) Draw a diagram to show the formation of poly(chloroethene) from n molecules of chloroethene. [3] (b) One chain contains 1500 monomer units. Calculate its relative formula mass (Mr). [2] (c) Explain why the repeating unit contains the same atoms as the monomer. [1]

9. (Higher tier only) This question is about condensation polymers.

(a) Give two ways in which condensation polymerisation differs from addition polymerisation. [2] (b) Glycine, H2NCH2COOH, forms a polypeptide. Name the two functional groups in glycine. [1] (c) Forty glycine molecules join to form one chain. How many water molecules are released? [1]

10. Living things contain naturally occurring polymers.

(a) Name the monomers of DNA, cellulose and protein. [3] (b) Describe the structure of most DNA molecules. [2]

11. A hydrocarbon C14H30 is cracked: C14H30 → C8H18 + 2A.

Compound A reacts with steam to give compound B. B is oxidised to compound C, which is an acid.

(a) Work out the formula of A and state which homologous series it belongs to. [2] (b) Name compounds B and C. [2] (c) Describe what you would see if A were shaken with bromine water, and explain why. [2] (d) Write a balanced equation for the complete combustion of A. [2] (e) Suggest what you would see when C is added to sodium carbonate solution. [1]

Answers

1. C4H10 and C5H12 (both fit CnH2n+2) [1]. C4H10 is butane [1]. [2] Examiner insight: Both correct formulae are needed for the first mark; a list with an extra wrong formula such as C4H8 usually loses it.

2. Crude oil is heated so that it evaporates [1]. The column is hotter at the bottom and cooler at the top [1]. Vapours rise and condense at the level where the temperature is below their boiling point [1]. Larger molecules have higher boiling points and condense lower down; smaller molecules condense higher up or leave as gases [1]. [4] Examiner insight: Answers that say heavier molecules “sink” gain no credit; the marks are for boiling point, evaporation, condensation and the temperature gradient.

3. (a) C6H14 [1]; it is more flammable (ignites more easily) because its molecules are smaller – or it is less viscous, or has a lower boiling point so it vaporises easily [1]. (b) Correct formulae CO2 and H2O as products [1]. 2C6H14 + 19O2 → 12CO2 + 14H2O [1]. [4] Examiner insight: Multiples such as C6H14 + 9½O2 → 6CO2 + 7H2O are usually accepted, but the balancing mark is lost if any atom count is wrong.

4. (a) The hydrocarbon is vaporised and mixed with steam [1], then heated to a very high temperature [1]. (b) C2H4 [1]. (c) Add bromine water and shake [1]; it turns from orange to colourless [1]. (d) Any two: there is high demand for fuels with small molecules [1]; alkenes are made, which are used to produce polymers or other chemicals [1]. [7] Examiner insight: “Goes clear” is not accepted for bromine water; you need the starting colour (orange) and the end colour (colourless) for both marks.

5. (a) Two carbons joined by a single bond [1]; one Cl on each carbon and two H on each carbon, with every bond shown [1].

      H   H
      |   |
 Cl - C - C - Cl
      |   |
      H   H

(b) Incomplete combustion (not enough oxygen reaches all the carbon, so carbon particles form) [1]. (c) Propane [1]; nickel catalyst [1]. [5] Examiner insight: In a displayed formula every bond must be drawn; writing CH2 groups or leaving the C=C in place loses the structure mark.

6. (a) Fizzing / bubbles / the sodium disappears [1]; hydrogen [1]. (b) Correct products CO2 and H2O [1]. 2C3H7OH + 9O2 → 6CO2 + 8H2O [1]. (c) Any two: yeast [1]; warm, about 30 °C, or absence of air [1]. [6] Examiner insight: “Heat” alone is not the same as warm conditions; a very high temperature kills the yeast, so a vague or wrong temperature can cost the mark.

7. (a) Fizzing / effervescence [1]; carbon dioxide [1]. (b) Ethyl ethanoate [1]; an ester [1]. (c) Ethanoic acid is a weak acid and only partially ionises in water [1]. Hydrochloric acid is a strong acid and ionises completely [1]. So the ethanoic acid solution has a lower concentration of H⁺ ions, giving a higher pH [1]. [7] Examiner insight: For (c) the third mark needs the link to H⁺ ion concentration; saying ethanoic acid is “more dilute” contradicts the question and gains nothing.

8. (a) Monomer drawn with C=C and n in front [1]; polymer drawn with a single C–C bond and Cl on one carbon [1]; brackets with extension bonds and n after the bracket [1].

      H   Cl               (  H   Cl )
      |   |                (  |   |  )
  n   C = C      →       —(— C - C —)—
      |   |                (  |   |  )
      H   H                (  H   H  ) n

(b) Mr of C2H3Cl = (2 × 12) + (3 × 1) + 35.5 = 62.5 [1]; 62.5 × 1500 = 93 750 [1]. (c) No other molecule is formed in the reaction (all atoms of the monomer end up in the polymer) [1]. [6] Examiner insight: Allow error carried forward in (b): a wrong monomer Mr multiplied correctly by 1500 still earns the second mark.

9. (a) Condensation monomers have two functional groups, while addition monomers have a C=C [1]; condensation releases a small molecule such as water, while addition forms only the polymer [1]. (b) Amine group (–NH2) and carboxylic acid group (–COOH) [1]. (c) 39 [1]. [4] Examiner insight: A “differ” question needs both sides of each comparison; stating only what condensation does, without the addition contrast, usually caps the credit.

10. (a) DNA: nucleotides [1]; cellulose: glucose (sugar) [1]; protein: amino acids [1]. (b) Two polymer chains [1] twisted into a double helix [1]. [5] Examiner insight: One mark per correct pairing; “sugar” is accepted for cellulose but “carbohydrate” is too vague for a named monomer.

11. (a) Carbon 14 − 8 = 6, hydrogen 30 − 18 = 12, shared between 2 molecules: C3H6 [1]; an alkene (fits CnH2n) [1]. (b) B: propanol [1]; C: propanoic acid [1]. (c) Orange to colourless [1], because A is unsaturated / has a C=C double bond that bromine adds across [1]. (d) Correct products CO2 and H2O [1]. 2C3H6 + 9O2 → 6CO2 + 6H2O [1]. (e) Fizzing / bubbles of gas [1]. [9] Examiner insight: Error carried forward applies across the parts: a wrong formula for A in (a), used consistently to name B and C, can still earn later marks.

Where marks are usually lost

• Describing distillation with weight or density instead of boiling point.
• Giving the flammability trend backwards.
• Writing “clear” for bromine water instead of colourless.
• Missing “steam” or “catalyst” in the conditions for making ethanol from ethene.
• Drawing an addition polymer with the C=C still present, without “n”, or without bonds through the brackets.
• Confusing oxidation of an alcohol (carboxylic acid) with its combustion (CO2 + water).
• Calling ethanoic acid weak because it is dilute (Higher tier).
• Counting water molecules in a chain as one per monomer instead of one per link (Higher tier).

Next steps

• Organic chemistry revision notes
• Organic chemistry study guide
• AQA GCSE Chemistry course hub
• Printable AQA GCSE Chemistry checklist
• All free 10-minute diagnostics
• Book a free trial class

Official syllabus

AQA GCSE Chemistry (8462) specification, for teaching from September 2016, GCSE exams June 2018 onwards, version 1.1, published by AQA – section 4.7 Organic chemistry.