• An ionic compound conducts electricity when it is molten or in solution
• The current causes the ionic compound to split up and form new substances.
• This process is called?electrolysis, a word which comes from Greek and means “splitting by electricity”
• Electrolysis?has many uses, including:
  • purifying copper
  • plating metals with silver and gold
  • extracting reactive metals, such as aluminium
  • making chlorine, hydrogen and sodium hydroxide

Electrolysis cells

• Electrolysis cells can be constructed using a beaker or crucible as the cell depending whether the ionic compound is in solution or molten
• For Standard Level Chemistry we only need to look at the electrolysis of molten ionic compounds

Electrolysis of a molten ionic compound

• In electrolysis, the substance that the current passes through and splits up is called the?electrolyte
• The electrolyte contains positive and negative ions
• What happens to these ions during electrolysis?
  • Negative ions?move to the?anode?and lose electrons - this is?oxidation
  • Positive ions?move to the?cathode?and gain electrons - this is?reduction
  • Electrically neutral atoms or molecules are released

Electrolysis of molten lead bromide

• The reactions which take place at the? electrodes can be shown by half equations
• When the positive lead ions move to the?cathode, they gain electrons in a?reduction?reaction:

Pb²⁺(aq) + 2e^-??? Pb(s)

• Similarly when the negative bromide ions move to the?anode?they lose electrons in an?oxidation?reaction:

?2Br^-(l) - 2e^-??? Br₂?(l)?

• Sometimes oxidation reactions are written with '+2e^-' on the right of the arrow instead of'-2e' on the left
• In this case the alternative half equation is:

?2Br^-(l) ? Br₂?(l)?+ 2e^-?

• Since metals are always?cations?and non-metal?anions, it is easy to predict the products of electrolysis of molten salts:
  • Metals?will always be formed at the?cathode?and?non-metals?at the?anode

Comparing Voltaic & Electrolytic Cells Summary Table