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S6 Chemistry: Electrochemical Cells (Paper 1: basics)
S6 Chemistry: Electrochemical Cells (Paper 1: basics)
Ten items on the negative electrode of a zinc-copper cell, the EMF formula, the salt bridge, 1.10 V, the magnesium-silver cell at 3.17 V, electron flow, the lead-copper cell at 0.47 V, the reversed cell at −1.10 V, the copper-silver cell at 0.46 V, and a misconception about electrons leaving the positive electrode.
Direct answers Answers in order: zinc, cathode minus anode, it completes the circuit and keeps the solutions neutral, 1.10 V, 3.17 V, from zinc to copper, 0.47 V and spontaneous, −1.10 V and not spontaneous, 0.46 V with silver positive, and electrons flow from the negative to the positive electrode.
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: Electrochemical Cells |
| Level | S6 |
02 Questions (10 items)
- FoundationIn a zinc-copper cell, which metal is the negative electrode?
- FoundationWhich formula gives the cell EMF from two standard electrode potentials?
- FoundationWhat does a salt bridge do in a cell?
- IntermediateWhat is the standard EMF of a zinc-copper cell (Zn²⁺/Zn at −0.76 V and Cu²⁺/Cu at +0.34 V)?
- IntermediateWhat is the standard EMF of a magnesium-silver cell (Mg²⁺/Mg at −2.37 V and Ag⁺/Ag at +0.80 V)?
- IntermediateWhen a zinc-copper cell discharges, which way do electrons flow in the external circuit?
- ChallengeWhat is the standard EMF of a lead-copper cell (Pb²⁺/Pb at −0.13 V and Cu²⁺/Cu at +0.34 V) and is the reaction spontaneous?
- ChallengeIf the zinc-copper reaction is reversed so that copper reduces zinc ions, what is the EMF?
- ChallengeWhat is the standard EMF of a copper-silver cell (Cu²⁺/Cu at +0.34 V and Ag⁺/Ag at +0.80 V) and which electrode is positive?
- Error redoA student says electrons flow from the positive to the negative electrode during discharge. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Zinc | Zinc has the more negative standard electrode potential, so it loses electrons more readily and is the negative electrode. |
| 2 | E°(cell) = E°(cathode) − E°(anode) | Cathode potential minus anode potential; a positive result means the discharge reaction is spontaneous. |
| 3 | It completes the circuit and keeps both solutions electrically neutral | Ions migrate through the bridge so that charge does not build up and stop the electron flow. |
| 4 | 1.10 V | 0.34 minus (−0.76) gives 1.10 V, with copper as the cathode and zinc as the anode. |
| 5 | 3.17 V | 0.80 minus (−2.37) gives 3.17 V because the two electrode potentials are far apart. |
| 6 | From the zinc electrode to the copper electrode | Zinc is the negative electrode, so electrons travel through the external circuit to the positive electrode. |
| 7 | 0.47 V and spontaneous | 0.34 minus (−0.13) gives 0.47 V and a positive value means the discharge reaction is spontaneous. |
| 8 | −1.10 V and the reaction is not spontaneous | Reversing the reaction reverses the cell, so the EMF changes sign and a negative value means external power is needed. |
| 9 | 0.46 V and silver is positive | 0.80 minus 0.34 gives 0.46 V, and silver with the higher potential is the cathode, that is the positive electrode. |
| 10 | Electrons flow from the negative electrode to the positive electrode through the external circuit | Oxidation at the negative electrode releases electrons, so they travel from the negative electrode to the positive one. |
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.
Compare the standard electrode potentials first, name the cathode and anode, subtract anode from cathode to get the EMF, then use the free energy change to judge feasibility.Tutor Registration →
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