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S5 Chemistry: Chemical Cells and Fuel Cells (Paper 4: misconception drill)
S5 Chemistry: Chemical Cells and Fuel Cells (Paper 4: misconception drill)
Ten misconception items on deciding the negative electrode, ionic conduction in the electrolyte, series and parallel voltage, non-rechargeable dry cells, water as the only fuel cell product, charge to moles and zinc consumed, and the electrode area myth.
Direct answers Answers in order: the more reactive metal is negative, ions carry the current, 6.0 V, it stays at 1.5 V, not rechargeable, water only, 0.010 mol, 0.33 g, 18 g, and area affects only current and capacity.
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: Chemical Cells and Fuel Cells |
| Level | S5 |
02 Questions (10 items)
- FoundationWhich metal is the negative electrode in a cell made of two metals, and what is the common error?
- FoundationWhat carries the current inside the electrolyte of a discharging cell?
- FoundationWhat is the total emf of four 1.5 V dry cells in series?
- IntermediateWhen two dry cells are in parallel, does the total emf become 3.0 V?
- IntermediateCan a used zinc-carbon dry cell be recharged?
- IntermediateWhat are the products of a hydrogen-oxygen fuel cell, and is carbon dioxide released?
- ChallengeA cell passes 965 C. How many moles of electrons is that, with the Faraday constant at 96500 C/mol?
- ChallengeThose 0.010 mol of electrons consume how much zinc at the negative electrode, zinc 65.4?
- ChallengeHow much water in grams is formed when 1 mol of hydrogen reacts completely in a fuel cell?
- Error redoA student claims that a larger electrode area gives a higher emf. What is the mistake?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | The more reactive metal is negative, while students wrongly pick the heavier or larger piece | The negative electrode is decided by reactivity, not by the density or the size of the metal. |
| 2 | The migration of positive and negative ions | There are no free electrons in the solution, so conduction is by moving ions. |
| 3 | 6.0 V | Emfs add in series, so 1.5 times 4 gives 6.0 V. |
| 4 | No, it stays at 1.5 V and only the available capacity increases | Parallel connection leaves the emf unchanged and merely doubles the charge that can be supplied. |
| 5 | No, its discharge reaction is not reversible | The electrode reactions cannot run backwards, and forcing a charge risks leaking. |
| 6 | Only water is produced, so no carbon dioxide is released | The reactants are hydrogen and oxygen, and the only product is water. |
| 7 | 0.010 mol | 965 divided by 96500 gives 0.010 mol. |
| 8 | 0.33 g | Two moles of electrons correspond to one mole of zinc, and 0.0050 mol times 65.4 gives 0.33 g. |
| 9 | 18 g | One mole of hydrogen forms one mole of water, which has a mass of 18 g. |
| 10 | The emf depends on the electrode materials and the electrolyte, while area only affects the current and capacity available | A larger area lowers the internal resistance and allows a bigger current, but the emf stays the same. |
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 every item state the direction of electron transfer or the formula first, then substitute the numbers and give the unit.Tutor Registration →
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