Chemistry · Rung 23 of 24

Batteries and electrolysis

A battery and an electrolysis are the same thing backwards. In a battery there is a redox reaction that wants to happen, and by splitting it into two halves the electrons that would pass straight from one reactant to the other have to go round the circuit: that detour is the current. They always leave the electrode that oxidises, because oxidising is losing electrons, and arrive at the one that is reduced, which is reduced precisely by picking them up; if you remember that oxidising is losing and reducing is gaining, the direction follows on its own. In electrolysis you do the opposite: current is pushed in from outside to force a reaction that would never happen by itself, like splitting water into hydrogen and oxygen or prising aluminium off the oxygen in its ore. And from that comes an everyday trick, galvanising: zinc gives up electrons more readily than iron, so it oxidises instead and spares the iron, and it goes on protecting it even when the layer is scratched, which is exactly what scratched paint does not do.

Where this sits

Comes after
Oxidation and reduction

Exercises from this rung

Generated by the app, from easiest to hardest

  1. What happens in a battery?

    • A reaction produces current
    • A wire heats up
    • A current forces a reaction
    • Electricity is stored with no reaction

    Why They are the same thing backwards. In a battery there is a reaction that wants to happen and, by splitting it in two halves, the electrons have to go round the circuit: that is the current. In electrolysis you do the opposite, pushing current in to force a reaction that would never happen on its own, like splitting water into hydrogen and oxygen.

    easier

  2. What happens in electrolysis?

    • A current forces a reaction
    • A wire heats up
    • A reaction produces current
    • Electricity is stored with no reaction

    Why They are the same thing backwards. In a battery there is a reaction that wants to happen and, by splitting it in two halves, the electrons have to go round the circuit: that is the current. In electrolysis you do the opposite, pushing current in to force a reaction that would never happen on its own, like splitting water into hydrogen and oxygen.

    in between

  3. In a battery, which electrode do the electrons leave from?

    • The one made of the heavier metal
    • The one that is reduced
    • The one touching the air
    • The one that oxidises

    Why From the one that oxidises, because oxidising is precisely losing electrons: they leave there, travel the circuit and reach the other one, which is reduced by picking them up. If you remember that oxidising is losing and reducing is gaining, the direction of the current follows and there is nothing to memorise.

    harder