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S6 Chemistry: Organic Synthesis Routes (Paper 2: Intermediate)
S6 Chemistry: Organic Synthesis Routes (Paper 2: Intermediate)
Ten items linking alcohol, aldehyde, acid and ester routes, with reduction, esterification and percentage yield.
Direct answers Answers in order: acidified dichromate under reflux, lithium aluminium hydride, concentrated hydrobromic acid, ethyl ethanoate, Tollens or Fehling reagent, hydrogen over nickel, 80 per cent, 4.5 g, 10.9 g, use reflux.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: S6 Chemistry: Organic Synthesis Routes |
| Level | S6 |
02 Questions (10 items)
- FoundationWhat reagents and conditions take ethanol to ethanoic acid?
- FoundationWhich reagent reduces ethanal back to ethanol?
- FoundationWhich reagent converts ethanol into bromoethane?
- IntermediateEthanoic acid and ethanol are heated with concentrated sulphuric acid. What forms?
- IntermediateBoth aldehydes and ketones give an orange precipitate with 2,4-dinitrophenylhydrazine. Which reagent separates them?
- IntermediateWhat conditions convert ethene into ethane?
- ChallengeThe theoretical yield of ethyl ethanoate is 11.0 g but only 8.8 g is obtained. What is the percentage yield?
- Challenge4.6 g of ethanol is oxidised to ethanoic acid with a 75 per cent yield. What mass is obtained? (46 and 60)
- ChallengeA nitrile route must give 7.4 g of propanoic acid. What mass of bromoethane is needed in theory? (74 and 109)
- Error redoError replay: a student distils ethanol with acidified dichromate expecting ethanoic acid. What is correct?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Acidified dichromate under reflux | Reflux keeps the ethanal in the flask so it is oxidised further, ending at ethanoic acid. |
| 2 | Lithium aluminium hydride in dry ether, or sodium borohydride | A hydride supplies hydrogen with a negative charge and turns the carbonyl group back into a hydroxyl group. |
| 3 | Concentrated hydrobromic acid with heat, or phosphorus tribromide | Bromide substitutes the hydroxyl group, which leaves as water under acid catalysis. |
| 4 | Ethyl ethanoate, with a fruity smell | An acid and an alcohol lose water to form an ester, and the reaction is reversible so the water must be removed. |
| 5 | Tollens reagent or Fehling solution | The hydrazine only proves a carbonyl group is present, and Tollens reagent reacts with aldehydes alone. |
| 6 | Hydrogen with a nickel catalyst and heat | Catalytic hydrogenation adds hydrogen across the double bond and gives the saturated alkane. |
| 7 | 80% | Percentage yield is actual over theoretical times one hundred, and 8.8 over 11.0 is 0.80. |
| 8 | 4.5 g | The theoretical mass is 6.0 g, and multiplying by 0.75 gives 4.5 g. |
| 9 | 10.9 g | 7.4 over 74 gives 0.10 mol of acid, which needs 0.10 mol of bromoethane, and that weighs 10.9 g. |
| 10 | Use reflux; distillation only gives ethanal | Distillation removes the intermediate ethanal before it can be oxidised, so the acid needs reflux and excess oxidant. |
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.
Draw one line in your notes from ethanol to ethanal to ethanoic acid to ethyl ethanoate, naming each reagent.Tutor Registration →
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