Oxygen in redox

  • Oxidation is the gain of oxygen.
  • Reduction is the loss of oxygen
CuO + H2 → Cu + H2O
Copper(ii)oxide is reduced to copper by hydrogen. 
Hydrogen is the reducing agent.
Hydrogen has been oxidised to water by coppper(ii)oxide. 
Copper(ii) oxide is the oxidising agent.

Oxidising and reduction agents

  • Oxidising agent is a substance which causes oxidation of another substance
  • Reducing agent is a substance which causes reduction of another substance


Hydrogen in redox

  • Oxidation is the loss of hydrogen by a substance
  • Reduction is the gain of hydrogen by a substance
H2 + Cl2 → 2HCl + S
H2S is oxidised, Cl2 is the oxidising agent
Cl2 is reduced, H2S is the reducing agent

Electron transfer in redox

  • Oxidation is the loss of elctrons
  • reduction is the gain of electrons
Oxidation Is the Loss of electrons 
Reduction Is the Gain of electrons

Oxidation states in redox

is the charge an atom would have if it existed as an ion. Oxidation is the increase of oxidation state by a substance and Reduction is the decrease of oxidation state by a substance. Rules of working out the oxidation states;

  • free elements have zero oxidation states eg Cu, Re
  • Oxidation state of an ion is its charge, eg Na+ = +1 O2- = -2
  • Oxidation states of some elements in their compounds is fixed eg Group 1 elements = +1
  • oxidation states of the elements in a compound adds up to zero eg NaCl : (+1) + (-1) = 0
  • sum of oxidation states of elements in an ion is equal to charge on the ion eg OH : (-2) + (+1) = -1

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