How a simple chemical cell works
Two different metals in an electrolyte create a voltage and a current.
A simple chemical cell needs three things:
- Two electrodes made of different metals.
- An electrolyte (a solution that conducts ions — e.g. salt water, dilute acid, or a fruit's juice).
- A wire connecting the electrodes externally.
What happens:
- The MORE REACTIVE metal LOSES electrons → forms positive ions → dissolves. It becomes the NEGATIVE electrode.
- The LESS REACTIVE metal GAINS electrons from the external circuit → it becomes the POSITIVE electrode.
- Electrons flow through the WIRE from the negative to the positive electrode — that's the current.
- Inside the electrolyte, ions flow to balance the charge.
The voltage of the cell depends on the DIFFERENCE in reactivity between the two metals:
- Magnesium and copper: ~2.7 V (Mg far above Cu).
- Zinc and copper: ~1.1 V.
- Copper and silver: ~0.5 V (close together).
A 'lemon battery' works because the lemon juice is acidic enough to be an electrolyte; two different metal nails (e.g. zinc-coated and copper) act as the electrodes.
- Two different metals + electrolyte + wire = chemical cell.
- More reactive metal = negative (oxidised).
- Less reactive metal = positive (reduced).
- Voltage depends on the difference in metal reactivities.