Electrolysis

• Electrolytes are substances that conduct electricity when dissolved or molten.
• Ions can move through the electrolyte, but neutral molecules cannot.
• In an acidic solution, hydrogen ions (H+) will be attracted to the cathode and chloride ions (Cl-) will be attracted to the anode.
• Oxidation occurs at the anode and reduction occurs at the cathode.
• The reaction at the cathode is H+(aq) + e- → H2(g), while the reaction at the anode is Cl-(aq) → Cl2(g).
• At the anode, oxygen gas is produced by oxidation of water molecules.
• At the cathode, electrons from the power supply reduce protons (hydrogen ions) into gaseous hydrogen atoms.
• Electrolysis


  Uses electricity to decompose a compound
• Electrolyte


  An ionic substance that's either molten or dissolved in water
• The free ions in an electrolyte conduct electricity and allow the whole thing to work
• For an electrical circuit to be complete, there's got to be a flow of electrons
• Cations


  Positive ions attracted to the negative cathode
• Anions


  Negative ions attracted to the positive anode
• Electrolysis of molten sodium chloride (NaCl)

  1. Sodium is produced at the negative cathode

  2. Chlorine is produced at the positive anode
• Oxidation


  Loss of electrons
• Reduction


  Gain of electrons
• Half-equations for electrolysis of molten NaCl

  1. Cathode: Na+ + e → Na

  2. Anode: 2Cl- → Cl2 + 2e-
• Sodium can be collected from the cathode and used in street lamps and as a coolant in some nuclear reactors
• Electrolysis of lead bromide (PbBr2)

  1. Cathode: Pb2+ + 2e → Pb

  2. Anode: 2Br- → Br2 + 2e-
• The product of the electrolysis at the cathode is lead, and at the anode is bromine
• Molten ionic salts contain only the ions of that salt, but dissolved in water there are also H+ and OH- ions to consider
• Simplest ion discharged at the anode

  The "simplest" ion is discharged, e.g. Cl- rather than OH-
• Ion discharged at the cathode

  A metal will be discharged if it's less reactive than hydrogen, otherwise hydrogen is discharged
• Electrolysis of aqueous sodium chloride solution

  1. At the cathode, 2H+ + 2e → H2

  2. At the anode, 2Cl- → Cl2 + 2e

  3. NaOH is left in the solution
• Copper can be obtained very easily from its ore by reduction with carbon, but the copper produced isn't pure enough for use in electrical conductors
• Electrolysis to obtain pure copper

  1. Cathode: Cu2+ + 2e → Cu

  2. Anode: Cu → Cu2+ + 2e

  3. Impurities are dropped at the anode as a sludge, whilst pure copper atoms bond to the cathode
• During electrolysis of copper sulfate solution using copper electrodes, the mass of the anode decreases and the mass of the cathode increases
• Demonstrating mass change during copper sulfate electrolysis

  1. Weigh the anode and cathode before

  2. Electrolysis for 5 minutes

  3. Weigh the anode and cathode again
• When an electric current passes through an ionic compound, it breaks down into its component ions.
• Ions can move through the liquid because they carry charge.
• At the cathode, hydrogen gas is produced by reduction of hydrogen ions.
• Aluminum is extracted from bauxite ore using electrolysis.
• The reaction at the anode involves the loss of electrons from water molecules, forming positively charged hydrogen ions and negatively charged oxygen ions.
• Water is split into its constituent elements using electrolysis.
• The overall reaction is the production of two moles of hydrogen per mole of water.
• Reduction occurs at the cathode, where electrons are gained by atoms/molecules.
• Oxidation occurs at the anode, where electrons are lost from atoms/molecules.
• The non-metal ions move towards the positive electrode (anode). Here they lose electrons to become neutral molecules or radicals that remain dissolved in the solution.