6.1 Introduction to electrolysis 

  • Ionic compounds are broken down by electricity (electrolysis). The electrolyte is the substance being broken down. To set up an electrical circuit for electrolysis, dip the anode connected to the positive terminal of the power supply and the cathode connected to the negative terminal into the electrolyte with a gap in between them. Electrode = conducting rod
  • The electrodes are made of inert substances so they don't react with the electrolyte. Cations (positive ions) move to the cathode; anions (negative ions) move to the anode, becoming elements.
  • Ionic compounds don't conduct electricity when solid because the ions can't move to carry the charge as they're in a fixed position in their giant lattice but when molten or dissolved or liquid, the ions can move and carry their charge.
  • Ionic substances have v high m.p.ts so it takes lots of energy to melt them and free the ions to move to electrodes. Predicting what will form is harder when electrolysing ionic compounds in solution because water also forms ions, so the productd at the electrodes are not always what you expect
  • Only metals below hydrogen are deposited from their aqueous solutions.
  • Covalent compounds can't be electrolysed unless ionised in water

6.2 Changes at the electrodes

  • Anions are oxidised (lose electrons) and cations are reduced (gaining electrons), becoming elements.
  • Half equations show what occurs at each electrode and to the electrons.
    • Pb2+ + 2e-


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