C3.4 - ELECTROLYSIS

• cathode?

  negative electrode
• anode?

  positive electrode
• when an electric current passes through a molten ionic compound, the compound decomposes or breaks down.

  • this process also occurs for aqueous solutions of ionic compounds
• why cant solid ionic compounds conduct electricity?

  no free ions to move and carry the charge
• basic set up of an electrolysis cell

  A) electrolyte

  
• cathode product will always be?

  metal
• the anode product will always be?

  non-metal
• • Aqueous solutions will always have water (H2O)
  • In the electrolysis of aqueous solutions, the water molecules dissociate producing H+ and OH– ions:

  H2O ⇌ H+ + OH–
• what is attracted to the positive elctrode?

  non metal ions and negatively charged OH- ions
• if halides ions (Cl-, Br-, I-) and OH- are present, then what will be discharged at the anode?

  the halide ion.

  • it will lose electrons and form a halogen (chlorine, bromine, or iodine)
• if no halide ions are present but OH- is, what will be discharged at the anode?

  OH- ion.

  • it will lose electrons and form oxygen
• what is attracted to the negative electrode?

  positively charged H+ ions, and metal ions
• what will be produced if the metal is above hydrogen in the reactivity series?

  hydrogen produced

  • bubbling will be seen at cathode
• why do we use inert electrodes such as graphite?

  they wont take part in the reaction, just provide a surface for the reactions to happen on
• what is electroplating?

  a process used to coat metals in a thin layer of a different metal
• How to purify copper.

  1. anode will be impure cuppor ore
  2. cathode is pure copper
  3. electrolyte is copper (II) sulfate solution
  4. at the anode, copper atoms lose electrons to become ions. as a result, the anode decreases in mass and impurities collect underneath.
  5. at the cathode, the copper ions from the electrolyte gain electrons to form copper atoms.
  6. copper collects at the cathode, causing the mass to increase.
• How to electroplate.

  1. cathode = object you want to coat e.g. spoon
  2. anode = metal you want to coat it with e.g. impure silver
  3. electrolyte = ions of coating material
  4. anode -> metal atoms lose electrons to form ions
  5. cathode -> metal ions gain electrons and are discharged on the surface of the metal that needs coating
• at the cathode, reduction or oxidation?

  positively charged ions gain electrons and are reduced
• at the anode, reduction of oxidation?

  negatively charged ions lose electrons and are oxidised
• what is the half equation at the cathode?

  Al(3+) + (3)e- = Al
• what is the half equation at the anode?

  2O(2-) = O2 + 4e-