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S6 Chemistry: Organic Synthesis Routes (Paper 4: Error Clinic)
S6 Chemistry: Organic Synthesis Routes (Paper 4: Error Clinic)
Ten items retraining three common slips: wrong reagents, distillation against reflux, and misused moles.
Direct answers Answers in order: concentrated sulphuric acid at 170 C, distillation, propanenitrile, neither gives a mirror, reversible, 170 C, 6.0 g, 0.10 mol, the carbon count is unchanged, a ketone.
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)
- FoundationError replay: a student heats ethanol with dilute sulphuric acid to dehydrate it. What is the correct condition?
- FoundationError replay: a student uses reflux to oxidise ethanol to ethanal. What is the right apparatus?
- FoundationError replay: a student says bromoethane with potassium cyanide gives propanol. What is the product?
- IntermediateError replay: a student says both ethanol and ethanoic acid give a silver mirror with Tollens reagent. What is correct?
- IntermediateError replay: a student calls esterification irreversible. What is correct?
- IntermediateError replay: a student writes 100 C for the dehydration of ethanol. What is the correct temperature?
- ChallengeError replay: a student works out that 4.6 g of ethanol gives 4.6 g of ethanoic acid. What is the correct mass?
- ChallengeError replay: a student treats 10.9 g of bromoethane as 1 mol. What is the correct amount?
- ChallengeError replay: a student says a nitrile loses one carbon on hydrolysis. What is correct?
- Error redoError replay: a student writes an aldehyde as the product of oxidising a secondary alcohol. What is correct?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Concentrated sulphuric acid heated to 170 C | Dilute acid cannot dehydrate, and only concentrated sulphuric acid removes the hydroxyl group as water. |
| 2 | Distillation, so the ethanal leaves at once | Under reflux the ethanal stays in the flask and is oxidised further, ending as ethanoic acid. |
| 3 | Propanenitrile, which gives propanoic acid only after hydrolysis | Cyanide substitutes the bromine to give a nitrile, and hydrolysis is a further step before the acid appears. |
| 4 | Neither gives a silver mirror, only aldehydes do | Tollens reagent oxidises aldehydes only, and neither an alcohol nor a carboxylic acid is reducing here. |
| 5 | It is reversible and needs sulphuric acid catalysis with water removed | Esterification and hydrolysis are two sides of one equilibrium, so water must be removed or excess alcohol used. |
| 6 | 170 C | 100 C is only the boiling point of water, and the dehydration needs concentrated sulphuric acid at 170 C. |
| 7 | 6.0 g | Ethanol is 46 and the acid 60, so the mass ratio is 60 to 46 and 4.6 g becomes 6.0 g. |
| 8 | 0.10 mol | Bromoethane has relative molecular mass 109, so 10.9 over 109 gives 0.10 mol. |
| 9 | The carbon count is unchanged and the nitrile carbon becomes the carboxyl carbon | Hydrolysis replaces the carbon nitrogen triple bond with two carbon oxygen bonds and loses no carbon. |
| 10 | A ketone | The hydroxyl carbon of a secondary alcohol is bonded to two carbons, so oxidation gives a ketone and not an aldehyde. |
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.
Write three numbers at the top of your notes: ethanol 46, ethanoic acid 60, bromoethane 109.Tutor Registration →
Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.