Summary Oxidation, Reduction and Redox Equations Notes - AQA Chemistry A Level

Oxidation, Reduction and Redox Equations
 Oxidation is loss, reduction is gain (of electrons)
 OIL RIG
 Reduction and oxidation occur simultaneously
 Oxidising agent – electron acceptor
 Reducing agent – electron donor
 Oxidation state – Hypothetical charge on an atom in a compound or an ion when that species,
regardless of the nature of bonding, is regarded as totally ionic

Oxidation State Rules
 Uncombined elements have an oxidation state of 0, and elements just bonded to identical
atoms also have an oxidation state of 0
o E.g. Mg (0), H2 (0)
 Oxidation state of a simple monoatomic ion is the same as its charge
o E.g. Na+ (+1), S2- (-2)
 Sum of all oxidation states in a compound is equal to 0
o E.g. MgCl2 (+2, -1, -1)
 Some metal elements have fixed oxidation states in compounds
o Group 1 metals - +1 in compounds
o Group 2 metals - +2 in compounds
o Group 3 metals - +3 in compounds
 Hydrogen is +1 in compounds, except in metal hydrides where it is -1
o E.g. H2O (+1, +1, -2), NaH (+1, -1)
 Oxygen is always -2, except in peroxides where it is -1
o E.g. CO2 (+4, -2, -2), H2O2 (+1, +1, -1, -1)
 Fluorine is always -1 as it is the most electronegative element
o E.g. HF (+1, -1)
 Halogens are also -1 except where the other element is more electronegative
o E.g. LiI (+1, -1), ICl (+1, -1)
 The sum of the oxidation numbers of the atoms making up a molecular ion equals the charge on
the molecular ion
o E.g. SO42- (+6, -2, -2, -2, -2 = -2)

Showing Oxidation States
 Sometimes, oxidation states aren’t clear from the formula of a compound
 Roman numerals are used in a chemical name to indicate the oxidation number
 E.g. Copper (II) sulphate – Cu +2

Half-Equations
 Overall equation for a redox reaction can be separated into two half equations – one shows
reduction and one shows oxidation