redox reactions

• Oxidation

  addition of oxygen eg.

  2Mg + O2 --> 2MgO

  
  

  loss of hydrogen eg.

  CH3OH --[O]--> CH2O + H2O

  
  

  loss of electrons eg.

  Al ----> Al3+ + 3e-
• Reduction

  loss of oxygen eg

  2CuO + C ---> 2Cu + CO2

  
  

  addition of hydrogen eg.

  C2H4 + H2 ---> C2H6

  
  

  gain of electrons eg.

  F2 + 2e- ---> 2F-
• oxidising agent

  -oxidises another atom or ion by causing it to lose electrons

  -itself gets reduces - it gains electrons

  -oxidation state of the oxidising agent decreases
• reducing agent

  -reduces another atom or ion by causing it to gain electrons

  -itself gets oxidised - loses electrons

  -oxidation state increases
• the oxidation state of any uncombined element is 0


  H2

  Zn

  O2
• many atoms or ions have fixed oxidation states in compounds

  group 1 = +1

  group 2 = +2

  fluorine is always -1

  hydrogen is always +1 (except in metal hydroxides)

  oxygen is always -2 (except in peroxides)
• oxidation state of an element in a mono-atomic ion is always same as the charge


  Zn2+ = 2+

  Fe3+ = 3+

  Cl- = 1-
• sum of the oxidation state in a compound is 0

  NaCl

  Na = +1

  Cl = -1

  NaCl = 0
• sum of oxidation state in ion is equal to the charge on the ion

  SO4 2-

  S = +6

  4xO = 4x(-2) = -8

  oxidation state = -2