Seneca
Sign up

Electrolysis

Applied Science: BTEC Level 3 National Extended Diploma, topic 4.2.3

Electrolysis

Electrolysis is the process that splits ionic compounds into their constituent (different) elements (the elements that make them up). Electrolysis happens using a solution that conducts electricity.

Electrolyte

Electrolyte

  • When ionic compounds are melted or dissolved in water, the ions (charged particles that have gained/lost electrons) are free to move around, and the liquid/solution will conduct electricity.
  • Ionic compounds that dissolve in water to make a solution that conducts electricity are called electrolytes.
Electrodes

Electrodes

  • When a voltage (direct current) is applied across an electrolyte, the charged ions are attracted to the electrode with the opposite charge to the ion.
  • Positively charged ions (cations) move to the negative electrode (cathode).
  • Negatively charged ions (anions) move to the positive electrode (anode).
Elements

Elements

  • When an ion touches an electrode, electrons can be transferred, producing elements.
  • E.g. if copper ions (Cu2+) are in a solution and a voltage is applied, they'll move to the cathode (negative electrode). When they touch the cathode, each Cu2+ ion will gain 2 electrons and form a copper metal.

Electrolysis of Aqueous Solutions

The products of the electrolysis of aqueous solutions are difficult to predict because the water molecules in the solution split up to form hydrogen (H+) and hydroxide (OH-) ions.

At the anode (positive electrode)

At the anode (positive electrode)

  • What is formed at the anode depends on if halide ions are present:
  • If halide ions are present, the respective halogen forms.
  • If halide ions are absent, oxygen forms.
At the cathode (negative electrode)

At the cathode (negative electrode)

  • What is formed at the cathode depends on the reactivity of the metal:
  • If the metal's more reactive than hydrogen, hydrogen is produced.
  • If the metal's less reactive than hydrogen, the metal is produced.

Test yourself on Electrolysis

  • What happens when we electrolyse molten copper oxide (CuO)?

  • Which ions are attracted to which electrode?

  • If copper ions (Cu2+) are in a solution and a voltage is applied, which electrode will they move towards and what will happen when they touch that electrode?

  • What happens when ionic compounds are dissolved in water?

  • An aqueous solution of copper(II) sulfate (CuSO4) contains Cu2+, SO42-, H+ and OH- ions. What happens when it is electrolysed?

Practise this topic for free