中文（繁體）
中文（简体）
English
S5 Chemistry: Electrolysis – Series Cells and Applications (Paper 3: Challenge)
S5 Chemistry: Electrolysis – Series Cells and Applications (Paper 3: Challenge)
Ten items on cells in series, concentration effects and the principles of electroplating.
Direct answers Answers in order: oxygen, 0.50 mol, aluminium, 0.15 mol, 0.90 g, almost unchanged, one to two, 11.5 g, equal in theory, no.
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)
- FoundationDilute sodium chloride solution is electrolysed with platinum electrodes. What forms at the anode?
- FoundationHow many moles of electrons does 48250 C represent?
- FoundationWhat forms at the cathode when molten alumina is electrolysed?
- IntermediateTwo cells are in series. The first deposits 0.30 mol of silver. How many moles of copper does the second deposit?
- IntermediateA current of 10 A runs for 965 s through molten alumina. What mass of aluminium forms? (Al = 27)
- IntermediateA copper anode is used in copper sulphate solution. How does the blue colour change after a while?
- ChallengeDuring the electrolysis of water, what is the volume ratio of the gas at the anode to the cathode?
- ChallengeMolten sodium chloride is electrolysed with 48250 C. What mass of sodium forms? (Na = 23)
- ChallengeIn nickel plating, how does the mass lost by the anode compare with the mass plated on the cathode?
- Error redoError replay: a student says the anode always gives off oxygen. Is that right?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Oxygen | The solution is dilute, so water is oxidised at the anode in preference to the few chloride ions. |
| 2 | 0.50 mol | Dividing the charge by 96500 gives the moles of electrons. |
| 3 | Aluminium | Aluminium ions are reduced at the cathode and liquid aluminium collects. |
| 4 | 0.15 mol | Cells in series share the electrons, so 0.30 mol of electrons reduces 0.15 mol of copper ions. |
| 5 | 0.90 g | The charge of 9650 C is 0.10 mol of electrons, so 0.033 mol of aluminium forms and that is 0.90 g. |
| 6 | It stays almost unchanged | The anode dissolves at the same rate as the cathode deposits, so the ion concentration stays roughly constant. |
| 7 | One to two, oxygen to hydrogen | The anode gives oxygen and the cathode gives hydrogen, and the mole ratio is one to two. |
| 8 | 11.5 g | Half a mole of electrons gives half a mole of sodium, which is 11.5 g. |
| 9 | They are equal in theory, so the bath concentration stays steady | Nickel ions from the anode replace those deposited, so the plating bath can be used for a long time. |
| 10 | No, the anode product depends on the electrolyte and the electrode material | Molten salts release halogens and a copper anode dissolves; only inert electrodes in water usually give oxygen. |
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.
For series cells start with equal electrons; for concentration questions compare discharge order.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.