C4 - Electrolysis

• Explain how a different product is formed in solution during this electrolysis.

  Hydrogen and Chlorine are produced.

  • 4 ions at the start: H+, OH-, Na+ and Cl-
  • H+ ion is discharged at negative electrode
  • Cl- ion is discharged at positive electrode
  • so OH- and Na+ remain in the solution
• Explain how oxygen gas is produced in the electrolysis of sodium sulphate solution

  • Water molecules
  • Break down to produce OH- ions
  • They are negatively charged and are attracted to the positive electrode
  • They lose electrons (oxidised)
  • To produce oxygen gas
• Explain the difference between the processes in electrolysis and in a chemical cell

  1. Electrolysis uses electricity to produce a chemical reaction
  2. A cell uses a chemical reaction to produce electricity
• Context: Students investigated the mass of copper produced at the negative electrode

  Question:

  Some of the copper produced did not stick to the negative electrode but fell to the bottom of the beaker.

  Suggest how the students could find the total mass of copper produced.

  1. Filter the mixture
  2. Wash and dry the copper
  3. Weigh the copper collected
  4. Add to the increase in mass of the electrode
• Why is Aluminium oxide mixed with cryolite?

  • Cryolite lowers the melting point (of aluminium oxide)
  • This reduces the amount of energy needed and saves money
• Oxidation half equation

  element -----> ion + electron
• Reduction half equation

  ion + electron -----> element