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S5 Chemistry: Alcohols, Carboxylic Acids and Esters (Paper 4: Error Replay)
S5 Chemistry: Alcohols, Carboxylic Acids and Esters (Paper 4: Error Replay)
Ten items retraining the usual slips in molar mass, equation coefficients and reversibility.
Direct answers Answers in order: 0.10 mol, 1.0 mol, 88, 4.4 g, 3O2, concentrated sulphuric acid catalyst, acid hydrolysis is reversible, 0.15 mol, about 3, 12 g.
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: S5 Chemistry: Alcohols, Carboxylic Acids and Esters |
| Level | S5 |
02 Questions (10 items)
- FoundationA student divides 4.6 g of ethanol by 92 and gets 0.05 mol. What is correct?
- FoundationA student writes one mole of glucose giving one mole of ethanol. How much ethanol does 0.50 mol of glucose actually give?
- FoundationA student writes 60 as the relative molecular mass of ethyl ethanoate. What is correct?
- IntermediateA student gives 2.4 g as the mass of 0.10 mol of carbon dioxide. What is correct?
- IntermediateA student writes 2O2 in the combustion equation of ethanol. What is correct?
- IntermediateA student thinks ethanoic acid and ethanol simply make an ester when warmed. Which condition is missing?
- ChallengeA student hydrolyses an ester with dilute sulphuric acid and calls it irreversible. What is correct?
- ChallengeA student calculates the ester from 0.20 mol of ethanol and 0.15 mol of acid using the ethanol. What is the correct maximum?
- ChallengeA student gives pH 1 for 0.10 mol/dm3 ethanoic acid. What is about right?
- Error redoError replay: for 0.30 mol of ethyl ethanoate a student answers 6 g of sodium hydroxide. What is correct?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 0.10 mol, dividing by 46 | The relative molecular mass of ethanol is 46, not 92; 92 belongs to the ester. |
| 2 | 1.0 mol | The coefficient before ethanol is two, so the amount of glucose is doubled. |
| 3 | 88 | 60 is ethanoic acid; the ester carries an extra ethyl group from ethanol, giving 88. |
| 4 | 4.4 g | Carbon dioxide has relative molecular mass 44; 24 is the molar volume, not the mass. |
| 5 | 3O2 | Two carbon dioxide and three water hold seven oxygen atoms; ethanol supplies one, so three oxygen molecules are needed. |
| 6 | Concentrated sulphuric acid as catalyst, with heating | Without a catalyst the reaction is very slow, and the acid also helps remove water from the equilibrium. |
| 7 | Acid hydrolysis is reversible; alkaline hydrolysis is not | Acid only catalyses the change, but alkali converts the acid into a salt so the reaction runs one way. |
| 8 | 0.15 mol, because the acid is limiting | Esterification is one to one, so the smaller amount of acid caps the product at 0.15 mol. |
| 9 | About 3 | Ethanoic acid is only partly ionised, so the hydrogen ion concentration is far below 0.10 mol/dm3. |
| 10 | 12 g | One ester needs one hydroxide, so 0.30 mol at 40 g per mole; the student halved the molar mass. |
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 46, 60 and 88 at the top of your notes and glance at them before calculating.Tutor Registration →
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