CC10 - electrolysis

• electrolysis is the use of electricity to split up ionic compounds, which the use of a DC current.
• an ionic compound with freely moving ions is called an electrolyte.
• solid compounds can be made electrolytes in two ways:

  melt the solid, or molten

  dissolve the solid, or aqueous
• the positive electrode is called the anode, and the negative electrode is called the cathode.
• a substance must meet 3 criteria to be used as an electrode:

  • must be able to conduct electricity
  • must have a high melting point
  • must be inert so it doesn’t react with the electrodes, graphite is typically used.
• positively charged ions are attracted to the negative cathode, and negatively charged ions are attracted to the positive anode, where the ions are discharged and turned back into neutral atoms.
• during aqueous electrolysis, water will split into H+ and OH- ions. The least reactive product will always form at the cathode- if it is more reactive than hydrogen, hydrogen will form as it is easier to turn hydrogen back into an atom since it is less stable.
• during aqueous electrolysis, the halogen will always form at the anode when present, and oxygen will form if a halogen is not present.
• reactivity series:

  • princess - potassium
  • steve - sodium
  • likes - lithium
  • cooking - calcium
  • mangoes - magnesium
  • and - aluminium
  • chili - carbon
  • zesty - zinc
  • is - iron
  • his - hydrogen
  • chili - copper
  • scrumptious - silver
  • good? - gold
• OIL RIG.

  oxidation is the loss of electrons, reduction is the gain of electrons.

  oxidation always occurs at the anode as non metals lose electrons.

  reduction occurs at the cathode as metals gain electrons.
• when copper electrodes are used to purify copper, pure copper is used at the cathode, and impure copper is used at the anode.

  at the anode, copper atoms lose electrons and become ions which migrate to the cathode, causing the cathode to gain mass- impurities in the anode collect below it as sludge, so the anode loses mass.

  the cathode gains mass as reduction occurs.

  copper sulphate is used so copper forms at the cathode and not other metals.