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S6 Chemistry: Chemical Cells and Electrolysis (Paper 2: intermediate)
S6 Chemistry: Chemical Cells and Electrolysis (Paper 2: intermediate)
Ten intermediate items on the reaction at a reactive copper anode, where the object goes in electroplating, the purpose of adding acid, the mass of copper dissolved by 9650 C, the mole ratio of hydrogen to chlorine, sodium from molten sodium chloride, moles of oxygen from 1930 C, the product at a carbon anode with the reason, the time for 5.00 A, and a misconception about the cathode product.
Direct answers Answers in order: copper dissolves, the cathode, to raise conductivity, 3.18 g, 0.500 mol, 4.60 g, 0.00500 mol, oxygen, 3860 s, and copper deposits at the cathode.
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: Chemical Cells and Electrolysis |
| Level | S6 |
02 Questions (10 items)
- FoundationWhen copper plates are used as the anode in the electrolysis of copper(II) chloride solution, what is the anode reaction?
- FoundationWhere should the object to be plated be placed in silver electroplating?
- FoundationWhy is a little sulphuric acid added when water is electrolysed?
- IntermediateCopper plates are used as both electrodes in the electrolysis of copper(II) sulphate solution. How many grams of copper dissolve at the anode after 9650 C has passed (F = 96500, Cu = 63.5)?
- IntermediateWhen concentrated salt solution is electrolysed, 0.500 mol of hydrogen forms at the cathode. How many moles of chlorine form at the anode at the same time?
- IntermediateIn the electrolysis of molten sodium chloride, 0.200 mol of electrons passes. What mass of sodium forms at the cathode (Na = 23.0)?
- ChallengeDuring the electrolysis of dilute sulphuric acid, 1930 C of charge passes. How many moles of oxygen form at the anode (F = 96500)?
- ChallengeWhat forms at the anode when copper(II) sulphate solution is electrolysed with carbon electrodes, and why?
- ChallengeHow many seconds of a 5.00 A current are needed to deposit 0.100 mol of copper (F = 96500, Cu = 63.5)?
- Error redoA student writes that chlorine is produced at the cathode when copper(II) chloride solution is electrolysed. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Copper is oxidised and dissolves, Cu to Cu2+ plus two electrons | A reactive electrode is oxidised more readily than water, so the anode dissolves and no chlorine is released. |
| 2 | At the cathode | Silver ions gain electrons at the cathode and deposit on the object, while a pure silver anode replaces them. |
| 3 | To increase the conductivity of the solution | Pure water has too few ions, so the acid supplies charge carriers and is not itself consumed. |
| 4 | 3.18 g | 9650 divided by 96500 gives 0.100 mol of electrons, each mole of copper corresponds to two moles of electrons, so 0.0500 mol times 63.5 gives 3.18 g. |
| 5 | 0.500 mol | Each electrode gives one mole of gas for every two moles of electrons transferred, so hydrogen and chlorine have the same number of moles. |
| 6 | 4.60 g | A sodium ion takes one electron, so each mole of electrons gives one mole of sodium and 0.200 times 23.0 is 4.60 g. |
| 7 | 0.00500 mol | 1930 divided by 96500 gives 0.0200 mol of electrons, and each mole of oxygen needs four moles of electrons, so 0.00500 mol forms. |
| 8 | Oxygen, because water is oxidised more readily than sulphate ions | In the competition for electrons at the anode water is oxidised before sulphate ions, so oxygen is released. |
| 9 | 3860 s | 0.100 mol of copper needs 0.200 mol of electrons, which is 19300 C, and that divided by 5.00 A gives 3860 s. |
| 10 | The cathode reduces copper ions to copper, and chlorine forms only at the anode | Chloride ions are oxidised only at the anode, while the cathode only supplies electrons to cations. |
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.
Decide first whether the cell is galvanic or electrolytic, name the products at each electrode, then work through charge, moles of electrons and atomic mass in order.Tutor Registration →
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