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S6 Chemistry: Chemical Cells and Electrolysis (Paper 1: basics)
S6 Chemistry: Chemical Cells and Electrolysis (Paper 1: basics)
Ten basic items on the products of electrolysing copper chloride solution, the terminal joined to the cathode, why salt solution conducts, the mass of copper from 3860 C, the hydrogen to oxygen volume ratio, charge from 2.50 A for 8 minutes, the anode product from molten lead bromide, the products from concentrated salt solution, the anode material in copper refining, and a misconception about the signs of the electrodes.
Direct answers Answers in order: copper and chlorine, the negative terminal, many mobile ions, 1.27 g, 30.0 cubic centimetres, 1200 C, bromine, chlorine with hydrogen, crude copper, and the anode joined to the positive terminal.
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(II) chloride solution is electrolysed with carbon electrodes, what forms at the cathode and at the anode?
- FoundationWhich terminal of the power supply is connected to the cathode of an electrolytic cell?
- FoundationWhy does salt solution conduct electricity while distilled water hardly does?
- IntermediateHow much copper, in grams, is deposited at the cathode when 3860 C of charge is passed through copper(II) chloride solution (F = 96500 C per mol, Cu = 63.5)?
- IntermediateWhen dilute sulphuric acid is electrolysed, 60.0 cubic centimetres of hydrogen is collected at the cathode. What volume of oxygen is collected at the anode at the same time?
- IntermediateWhat charge in coulombs passes when a current of 2.50 A flows for 8.00 minutes?
- ChallengeWhat is produced at the anode when molten lead(II) bromide is electrolysed?
- ChallengeWhat are the products at the anode and the cathode when concentrated salt solution is electrolysed?
- ChallengeWhat material is used as the anode in the electrolytic refining of copper?
- Error redoA student says the anode of an electrolytic cell is the negative electrode because the anode of a galvanic cell is negative. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Copper at the cathode and chlorine at the anode | Reduction at the cathode gives copper while oxidation of chloride ions at the anode gives chlorine. |
| 2 | The negative terminal | Electrons flow from the negative terminal to the cathode so that cations there can gain electrons. |
| 3 | Salt solution contains many mobile ions and distilled water has very few | Conduction depends on mobile ions in the solution rather than on the water molecules themselves. |
| 4 | 1.27 g | 3860 divided by 96500 gives 0.0400 mol of electrons, each mole of copper needs two moles of electrons, so 0.0200 mol times 63.5 gives 1.27 g. |
| 5 | 30.0 cubic centimetres | The volume ratio of hydrogen to oxygen in the electrolysis of water is 2 to 1, so oxygen is half the volume of hydrogen. |
| 6 | 1200 C | Charge is current times time, and the time must be in seconds, so 8.00 times 60 gives 480 s and that times 2.50 gives the charge. |
| 7 | Bromine | A molten salt contains ions only, so bromide ions are oxidised to bromine at the anode while lead forms at the cathode. |
| 8 | Chlorine at the anode and hydrogen at the cathode | Chloride ions are oxidised more readily than hydroxide ions so chlorine forms at the anode, while water is reduced to hydrogen at the cathode and sodium hydroxide is left in solution. |
| 9 | Crude copper, that is impure copper | Crude copper at the anode dissolves into copper ions, pure copper is deposited at the cathode and impurities settle as sludge. |
| 10 | The anode of an electrolytic cell is connected to the positive terminal, and only a galvanic anode is negative | An electrolytic cell is driven by an external supply that pulls electrons away from the anode, so the anode is positive and oxidation occurs there. |
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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