What pupils do
Four steps, each one tap. Pick a metal from the rack — it slides into the left of the beaker. Pick a second for the right. The voltmeter reads, the electrodes get labelled negative − and positive +, and their two metals light up on the reactivity board. Then they close the switch to light the lamp, watch the reactive electrode dissolve away until the cell goes flat, and connect a charger to reverse it.
Two buttons open up the extension: Add another cell (up to three, wired in series) and Light the lamp.
The readings
Four metals, so ten combinations. Voltages are the differences in standard electrode potential:
| Pair | Voltage | Pair | Voltage |
|---|---|---|---|
| Mg – Cu | 2.71 V | Zn – Cu | 1.10 V |
| Mg – Fe | 1.93 V | Fe – Cu | 0.78 V |
| Mg – Zn | 1.61 V | Zn – Fe | 0.32 V |
| any metal with itself | 0.00 V |
Worth knowing before the class practical: these are the calculated values. A real beaker of salt solution gives noticeably less — Mg/Cu often reads nearer 1.6–2.0 V — because the electrolyte isn’t a solution of each metal’s own ions. The pattern holds exactly; the absolute numbers don’t. If your class measures first and simulates after, name that gap rather than letting them find it.
Spec coverage
- A simple cell = two different metals in contact with an electrolyte
- The voltage depends on the metals used — the wider apart in the reactivity series, the bigger the reading
- Batteries are two or more cells in series, and the voltages add (2.71 × 3 = 8.13 V on screen)
- In non-rechargeable cells the reactions stop when a reactant is used up — pupils watch the magnesium physically disappear
- Rechargeable cells reverse their reactions when an external current is supplied; alkaline cells can’t
Questions worth asking
- Before they touch it: rank the six pairs from biggest to smallest voltage. Then test.
- Why does magnesium and magnesium give nothing? This one catches almost everyone.
- Which electrode gets eaten? Why that one? The more reactive metal is losing electrons — that’s why it’s negative and why it’s the one that runs out.
- Three cells gave 8.13 V. Did the current triple too? It didn’t, and the lamp doesn’t get three times brighter.
- Data-handling: plot voltage against difference in reactivity, straight line, predict a pair not on the rack.
Misconceptions it goes after
That the positive electrode is the reactive one (it’s the opposite). That “flat” means the electricity ran out rather than a chemical being used up. That any two metals will do. That adding cells adds current.
Adaptation options in the Accessibility menu
Buttons only (named buttons for each metal, nothing to hit in the 3D scene), extra slow for the run-down and recharge, electrode labels on or off, reactivity board on or off, method checklist on or off, voltmeter readout on or off. Plus the standard suite: dark navy theme, Irlen overlays, reading ruler, wider letter spacing, text size, high contrast, projector mode, reduced/slowed motion, protanopia and deuteranopia filters. Every step is announced to screen readers with both electrodes named.
Where it fits
10–15 minutes as a front-of-class demo before the metals-in-beakers practical, or 25–30 minutes on tablets with a results table to fill in. It pairs naturally with your reactivity series lesson — the board on the back wall is the same ladder they’ve already met.