OXIDATION - redox

• what does OILRIG stand for?


  Oxidation

  Is

  Loss of electrons

  Reduction

  Is

  Gain of electrons
• what has been reduced and oxidised in this reaction?

  Ca + 1/2 O2 → CaO

  1/2O2 -> O2- = reduction

  Ca -> Ca2+ = oxidation
• what are reducing agents?

  substance that is oxidised - loses electrons
• what are oxidising agents?

  substance that has been reduced - gain electrons
• rules for working out oxidation states?

  1. uncombines elements are always 0
  2. hydrogen = +1 except in hydrides (-1)
  3. chlorine = -1 except in compounds with F+O e.g. CLF3 = +3
  4. fluorine is most electronegative = -1
  5. oxygen = -2 except in peroxides -1 and +2 in OF2
• work out the oxidation states of....?

  N in NH3 = +1x3= +3 so N = -3

  S in H₂S = -2

  H2 in H2O2 = oxygen = -1 so H = +1

  S in H₂SO₄ = +6

  S in SO₄²⁻= -2

  V in VO2+ = +4

  V in VO2+ = +5
• REDOX equation?

  2Na + Cl2 -> 2NaCl 

  0 0 +1 -1

  Na = oxidation (lost an electron) - reducing agent

  Cl = reduction (gained an electron) - oxidising agent
• rules for balancing half equations?

  1. balance atoms for e.g.  Cl2 → 2Cl
  2. balance oxygens
  3. balance hydrogens
  4. balance charges with electrons
• half equations...?

  Fe2+ -> Fe3+ + e

  2+ 3+

  = oxidation
• half equations...?

  MnO4- + 8H+ + 5e- → Mn2+ + 4H2O

  = reduction
• combining half equations?

  Fe2+ -> Fe3+ + e- (x5)

  MnO4- + 8H+ + 5e- → Mn2+ + 4H2O

  = MnO4- + 8H+ + 5Fe2+→ Mn2+ + 4H2O + 5Fe3+

  REDOX REACTION