Redox

• Oxidation number = number of electrons involved in bonding to a different element, based on a set of rules that apply to atoms
• Oxidation = loss of electrons, increase in oxidation number, +
• Reduction = gain of electrons, decrease in oxidation number, -
• Redox reaction = reaction involving reduction and oxidation
• Oxidation state rules:

  H = +1

  O = -2

  F = -1

  G1 = +1

  G2 = +2

  ion = charge

  uncombined elements = 0 e.g Cl2
• Exceptions to oxidation state rules:

  • other halogens = -1 except with F or O
  • H = +1 except in metal hydride e.g NaH
  • O =-2 except with F or in Peroxides
• What is the oxidation number of S in H2SO4?

  Total H = (+1 x 2) = +2

  Total O = (-2 x 4) = -8

  Total Charge = 0

  x + 2 - 8 = 0

  x + 2 = 8

  x = +6

  Oxidation number of Sulfur is +6
• Zn + 2HCl -> ZnCl2 + H2

  0 ——————>+2

  +2 ———————>0

  Zn is Oxidised

  H is Reduced
• Chlorate (V)

  formula: ClO-

  Oxidation number = +5

  O = -2

  5 - 2 = -1

  3 requires -4 = -1

  -4 + -2 = -6

  -2 goes into -6, 3x

  Formula = ClO3-
• ClO3-

  X + (-2 x 3) = -1

  X - 6 = -1

  X = 5

  Chlorate (V)
• Disproportionation = when an element is simultaneously oxidised and reduced
• Half Equations:

  Mg + Cl2 —> MgCl2

  0 0 +2 -2

  Mg —> Mg2+ + 2e- Oxidised

  Cl2 + 2e- —> 2Cl- Reduced