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S6 Chemistry Organic Chemistry, Paper 1: alcohols, carboxylic acids, esters and polymers
S6 Chemistry Organic Chemistry, Paper 1: alcohols, carboxylic acids, esters and polymers
Ten graded items on the molar masses of ethanol and ethanoic acid, esterification, the hydrogencarbonate test, dehydration, two-step oxidation, saponification and addition polymers, each with an answer.
Focus Work out molar mass before moles, one acid plus one alcohol gives one ester and water, only carboxylic acids release carbon dioxide with hydrogencarbonate, and yields multiply the theoretical amount.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 25 |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: S6 Chemistry: Organic Chemistry (Functional Groups) |
| Level | Four basic, three advanced, two challenge and one error-repair item |
02 Questions (10 items)
- FoundationFind the molar mass of ethanol, C2H5OH, and the number of moles in 4.6 g.
- FoundationFind the molar mass of ethanoic acid, CH3COOH, and the mass of 0.50 mol.
- FoundationEthanoic acid and ethanol are heated with concentrated sulphuric acid. What is formed, and what is its molar mass?
- FoundationEthanoic acid is added to sodium hydrogencarbonate solution. Which gas is released, and how many moles from 0.10 mol of the acid?
- IntermediateEthanol vapour over hot alumina dehydrates to ethene. What mass of ethene comes from 0.10 mol of ethanol?
- IntermediateEthanol is oxidised in two steps to ethanoic acid. By what mass does 0.20 mol increase?
- IntermediateSaponification needs 3 mol of sodium hydroxide per mole of triglyceride. What amount and mass is needed for 0.050 mol?
- ChallengePoly(ethene) is an addition polymer with a repeat unit of C2H4, molar mass 28.0. How many moles of repeat units are in 1.0 kg?
- Challenge0.50 mol of ethanoic acid and 0.50 mol of ethanol give an 80% yield of ester. Find the amount and mass obtained.
- Error redoError repair: a student writes that both ethanol and ethanoic acid turn blue litmus red. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 46.0 g per mole, so 0.10 mol | 24.0 plus 6.0 plus 16.0 is 46.0, and 4.6 divided by 46.0 is 0.10. |
| 2 | 60.0 g per mole, so 30.0 g | 24.0 plus 4.0 plus 32.0 is 60.0, and 0.50 times 60.0 is 30.0 g. |
| 3 | Ethyl ethanoate, with a molar mass of 88.0 | Acid plus alcohol gives an ester and water, and ethyl ethanoate C4H8O2 has a mass of 88.0. |
| 4 | Carbon dioxide, 0.10 mol | Only the carboxylic acid releases carbon dioxide with hydrogencarbonate, one mole per mole, so 0.10 mol gives 0.10 mol. |
| 5 | 2.8 g | Each mole of ethanol gives one mole of ethene, so 0.10 times 28.0 is 2.8 g. |
| 6 | An increase of 2.8 g | Ethanol at 46.0 becomes ethanoic acid at 60.0, a gain of 14.0 per mole, so 0.20 times 14.0 is 2.8 g. |
| 7 | 0.150 mol, which is 6.0 g | 0.050 times 3 is 0.150 mol, and 0.150 times 40.0 is 6.0 g of sodium hydroxide. |
| 8 | About 35.7 mol | 1,000 divided by 28.0 is 35.7, since polymerisation does not change the mass of each repeat unit. |
| 9 | 0.40 mol, which is 35.2 g | Theoretical yield is 0.50 mol from the one-to-one ratio, and 80 per cent of that is 0.40 mol, which times 88.0 is 35.2 g. |
| 10 | Wrong: only the carboxylic acid is acidic enough to turn litmus red | The carboxyl group releases hydrogen ions, whereas the hydroxyl group in ethanol does not ionise, so the solution stays neutral. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
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