electrolysis pt 2

• what is electrolysis?


  electrolysis is separating ionic compounds into their elements by using electricity.
• why are the electrodes made using graphite?

  they have a low reactivity, they're conductive, have a high melting point
• why is the ionic substance molten or in solution?

  so that ions are free to move and carry charge through the substance as the electrons are delocalised.
• cons of electrolysis of molten ionic substances?

  uses lots of energy

  very expensive

  specialised vessels are required
• cons of electrolysis of dissolved ionic substances?

  sometimes an undesireable product is made
• what changes at the electrode?

  positive ions gain electrons from the negatively charged cathode. they change from ions to atoms. negative ions lose electrons at the positively charged anode. they change from ions to atoms.
• what happens when negative ions are attracted to the anode?

  if ion is a halide (chlorine, bromine or iodine)the halide is produced is produced, if not, oxygen is produced.

  4OH--> 2H2O+O2+4e-
• what happens when positive ions are attracted to the cathode?


  if they metals are more reactive than hydrogen, hydrogen is produced

  the equation for this is 2H+ +e- -> H2

  if they are less reactive, the metal is produced (copper, gold,silver,platinum)
• what happens when an ionic solution is dissolved in water?

  the ions H+ and OH- are also present.

  e.g. molten zinc oxide ions = Zn2+ and Cl-

  -> dissolved zinc chloride = Zn2+, Cl-, H+, OH-
• what are the products of the electrolysis of brine?

  chlorine gas (discharged at anode)

  hydrogen gas (discharged at anode)

  sodium hydroxide (remains in solution)
• what is chlorine gas useful for?

  killing bacteria in water, bleach, PVC
• what is hydrogen gas used for?

  making margarine, and fertilisers, used for rocket fuel
• what is sodium hydroxide used for?

  used in many chemical reactions (making soap), neutralising acids and making paper