Oxidation and Reduction

Oxidation and Reduction

1. Introduction to oxidation and reduction

   • Oxidation
     • is the loss of electrons.
   • Reduction
     • is the gain of electrons.
   • Hint* OILRIG (Oxidation is loss, Reduction is Gain)
   • Redox
     • Oxidation and reduction always occur together and they depend on each other too.
   • Oxidation numbers
     • it is written with the sign first and followed by the number, -1 or +2 for example
     • Atoms in the elemental state have an oxidation number of zero
     • Simple ions, the oxidation number is the same as the charge on the ion.

2. Redox equations

   • Half equations
     • Electrons are added on both sides to balance the charges
     • e.g. Zn (s) + Cu2+ (aq) -> Zn2+ (aq) + Cu (s)
       • 1. Zn (s) -> Zn2+ (aq) + 2e-
       • 2. Cu2+(aq) + 2e- -> Cu
       • There MUST be an equal amount of electrons so they can be cancel out
       • Add the two half equations, and the final answer should be balanced
   • Oxidizing and reducing agents
     • An oxidizing agent is reduction and a reducing agent is oxidation

3. Reactivity

   • Reactivity series of metals
     • Strongest Mg->Al->Zn->Fe->Pb->Cu->Ag Weakest
   • Series of non metals F2->Cl2->Br2->I2
   • If the metal isn't a strong reducing agent then reaction will not occur
   • A more reactive non-metal is able to oxidize the ions of a less reactive non-metal

4. Voltaic Cells

   • Voltaic cell is basically a battery
   • Half cell
     • Is allowing the electrons to flow in between and this is created by two half equations
     • Connected half cell is "Electrodes"
   • Voltaic cell
     • two half cells make up a voltaic cell
     • Oxidation always occurs at anode and reduction always occurs at the cathode. Anode has a negative charge and Cathode has a positive charge
     • Electrons always flow from anode to cathode
   • Salt Bridge completes the circuit and balances out the charges of the aqueous solution
   • it takes the energy of a spontaneous redox reaction to produce electric voltage

5. Electrolytic Cells

   • it uses an external source of voltage to bring about a redox reaciton that would otherwise be non-spontanous.
   • electrolysis enables neutral elements to be released from ionic compounds by discharging the ions
   • Requires the source of power
   • Electrolyte
     • a liquid that conducts electricity
   • Electrodes
     • These are conducting substances such as a metal or graphite
   • At the anode, negative ions lose electrons, at the cathode, positive ions gain electrons.