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S5 Chemistry: Alcohols, Carboxylic Acids and Esters (Paper 3: Challenge)
S5 Chemistry: Alcohols, Carboxylic Acids and Esters (Paper 3: Challenge)
Ten items on combustion equations, limiting reagents, saponification and titration, all requiring calculation.
Direct answers Answers in order: 3, 22 g, soap and glycerol, 7.2 dm3, 13.2 g, 48 g/dm3, 12 g, 102, 75%, 0.30 mol.
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)
- FoundationIn the equation for the complete combustion of ethanol, what number goes before oxygen?
- Foundation0.25 mol of ethanol burns completely. What mass of carbon dioxide forms?
- FoundationWhen a fat is heated with sodium hydroxide solution, what is produced?
- Intermediate0.10 mol of ethanol burns completely. What volume of oxygen is needed? (24 dm3 per mole)
- Intermediate0.20 mol of ethanol reacts with 0.15 mol of ethanoic acid. What is the maximum mass of ester? (Mr 88)
- Intermediate25.0 cm3 of vinegar is neutralised by 25.0 cm3 of 0.80 mol/dm3 sodium hydroxide. What is the acid concentration in g/dm3?
- Challenge0.30 mol of ethyl ethanoate is fully hydrolysed by alkali. What mass of sodium hydroxide is needed? (NaOH 40)
- ChallengeEthanol reacts with propanoic acid. What is the relative molecular mass of the ester formed? (C5H10O2)
- Challenge360 g of glucose should give 184 g of ethanol but only 138 g is collected. What is the percentage yield?
- Error redoError replay: a student says 0.10 mol of ethanol needs 0.10 mol of oxygen. What is correct?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 3 | Balance carbon and hydrogen first: two carbon dioxide and three water need seven oxygen atoms, one comes from ethanol, so oxygen takes 3. |
| 2 | 22 g | Each mole of ethanol gives two moles of carbon dioxide, so 0.50 mol times 44. |
| 3 | Soap (sodium salts of fatty acids) and glycerol | A fat is an ester; alkaline hydrolysis turns the fatty acids into sodium salts, which is soap. |
| 4 | 7.2 dm3 | Each mole of ethanol needs three moles of oxygen, so 0.30 mol times 24. |
| 5 | 13.2 g | The acid is limiting at 0.15 mol, so at most 0.15 mol of ester can form. |
| 6 | 48 g/dm3 | The alkali is 0.020 mol and the acid is one to one, so 1.20 g in 0.025 dm3 of solution. |
| 7 | 12 g | The ester and the alkali are one to one, so 0.30 mol at 40 g per mole. |
| 8 | 102 | Five carbons, ten hydrogens and two oxygens give 60 plus 10 plus 32. |
| 9 | 75% | Divide the actual mass by the theoretical mass: 138 over 184 is 0.75. |
| 10 | 0.30 mol | The equation needs three moles of oxygen per mole of ethanol; the student ignored that coefficient. |
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 the balanced equation first, then decide which reactant runs out first.Tutor Registration →
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