ES 1

• Electrolysis can be conducted using ionic compounds that are either molten or dissolved in solution
• Metallic bonding and graphite can conduct electricity due to free-moving electrons
• Electrolysis involves two electrodes: the anode (positive electrode) and the cathode (negative electrode)
• Cations are positive ions, anions are negative ions
• The electrodes must not touch to ensure the charge is carried through the solution
• Solids will plate the electrode and bubbles indicate gas production during electrolysis
• Electrolysis of molten substances is relatively straightforward compared to electrolysis of solutions
• Electrolysis of molten substances produces elements that make up the ionic compounds
• Anions are attracted to the anode and give up electrons


  Cations are attracted to the cathode and receive electrons
• Graphite can be used in electrolysis for electrodes
• Electrolysis is the breaking down of a substance using electricity
• Substances collect at the electrodes during electrolysis
• Electrodes are made from inert conductive materials like platinum and graphite
• Ions need to be free to move around to conduct electricity during electrolysis
• For example, electrolysis of molten sodium chloride produces sodium and chlorine gas
• Reactions at each electrode can be shown using half equations

  At the anode, negative ions give up electrons to form atoms, at the cathode, positive ions accept electrons to form atoms
• If the metal at the cathode is less reactive than hydrogen

  A metal is formed
• If the solution at the anode doesn't contain a halide ion (chloride, bromide, iodide)


  Oxygen is formed from OH- ions in water
• Electrolysis of ionic compounds

  If sodium chloride is taken, it will produce sodium and chlorine gas. Sodium forms at the cathode, while chlorine gas forms at the anode. At the anode, Cl- ions are attracted to the positive anode, forming Cl2 + 2 electrons. At the cathode, Na+ ions are attracted to the negative cathode, where Na+ picks up an electron to form sodium metal. If the substance is molten, the process is different compared to when it is in aqueous solution due to the presence of extra ions like OH- and H+ from water.
• Electrolysis of brine

  Halogens like chlorine can be extracted through the electrolysis of brine, which is a high concentration solution of salts such as chlorides, bromides, and iodides. Brine can be obtained from seawater due to the minerals dissolved in rivers that flow into the sea, making the sea salty. The salt content in seawater can be used to extract halogens.
• If the salt solution is dilute

  Oxygen is formed
• The products formed at each electrode in electrolysis depend on the reactivity of the ions and the concentration of the salt solution
• If the solution at the anode is concentrated and contains a halide ion


  The halogen is formed (chlorine, bromine, iodine)
• If the metal at the cathode is more reactive than hydrogen

  Hydrogen gas is formed
• Electrolysis can be useful for purifying certain metals like copper
• Redox reactions involve the transfer of electrons, with oxidation being the loss of electrons and reduction being the gain of electrons
• If the solution is dilute, oxygen is produced instead of chlorine during electrolysis
• Electrolysis of sodium chloride solution

  At the cathode, H+ ions from water form hydrogen gas. At the anode, Cl- ions from the salt form chlorine gas. More reactive ions remain in solution and react with hydroxide ions to produce sodium hydroxide
• Extraction of halogens

  Halogen extraction process from rocks to obtain salt, hydrogen gas, and chlorine gas
• Sodium chloride solutions must be concentrated for chlorine extraction via electrolysis
• Extraction of bromine and iodine

  Using displacement reactions with a more reactive halogen to extract bromine and iodine from brine solutions
• Calcium is oxidized by losing electrons to form calcium ions, while oxygen is reduced by gaining electrons to form CO2
• Reduction

  The process of gaining electrons
• Oxidizing agents


  Gain electrons and reduce themselves
• Oxygen is being reduced in this reaction because it's gaining electrons to form CO2
• Iron in Fe2O3 is in a +3 oxidation state
• Rules for assigning oxidation numbers

  • Uncombined elements are always zero
  • Group ones are always +1
  • Group twos are always +2
  • Group threes are always +3
  • Hydrogen is +1 except in hydrides where it's -1
  • Oxygen is -2 except in peroxides and OF2
  • Transition metals have variable oxidation states
• Vanadium in vanadium oxide is in a +4 oxidation state
• Oxidation

  The process of losing electrons
• Reducing agents

  Lose electrons and are oxidized themselves