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S5 Chemistry: Electrolysis – Error Replay (Paper 4)
S5 Chemistry: Electrolysis – Error Replay (Paper 4)
Ten items retraining the common slips in unit conversion and electron counting.
Direct answers Answers in order: 600 C, copper, chlorine, 0.010 mol, 0.20 mol, hydrogen, 21.6 g, about 0.050 mol, carbon oxidised to carbon dioxide, 3600 C.
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: Electrolysis and Industrial Applications |
| Level | S5 |
02 Questions (10 items)
- FoundationA current of 1.0 A flows for 10 minutes. What is the charge?
- FoundationWhat is obtained at the cathode during the electrolysis of copper sulphate solution?
- FoundationWhat is obtained at the anode when molten sodium chloride is electrolysed?
- IntermediateHow many moles of electrons does 965 C represent?
- Intermediate0.40 mol of electrons passes through copper sulphate solution. How many moles of copper deposit?
- IntermediateWhat is obtained at the cathode when dilute sulphuric acid is electrolysed?
- ChallengeSilver plating passes 0.20 mol of electrons. What mass of silver deposits? (Ag = 108)
- ChallengeA current of 4.0 A flows for 1200 s. How many moles of electrons pass?
- ChallengeWhy do the carbon anodes wear away during aluminium extraction?
- Error redoError replay: a student puts 30 into the formula for 2.0 A and 30 minutes and gets 60 C. What is correct?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 600 C | Ten minutes is 600 seconds, and one ampere for that long gives 600 C. |
| 2 | Copper | Copper ions are reduced at the cathode and the metal deposits. |
| 3 | Chlorine | Chloride ions lose electrons at the anode and chlorine molecules form. |
| 4 | 0.010 mol | Dividing by 96500 gives the answer, and 965 is one hundredth of that value. |
| 5 | 0.20 mol | Copper ions take two electrons each, so the number of moles is halved. |
| 6 | Hydrogen | Hydrogen ions are reduced at the cathode and hydrogen gas is released. |
| 7 | 21.6 g | Silver ions take one electron each, giving 0.20 mol of silver, which is 21.6 g. |
| 8 | About 0.050 mol | The charge is 4800 C, and dividing by 96500 gives about 0.0497 mol. |
| 9 | The carbon is oxidised to carbon dioxide | Oxygen produced at the anode reacts with carbon, so the anodes must be replaced regularly. |
| 10 | 3600 C | Time must be in seconds: 30 minutes is 1800 s, and 2.0 A for that long gives 3600 C. |
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 seconds and the electron count before calculating; that removes half the slips.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.