AQA A Level Chemistry - Redox

define oxidation

process of electron loss/gain of oxygen

what is an oxidising agent?

electron acceptor, reduced itself

define reduction

process of electron gain/loss of oxygen

what is a reducing agent?

electron donor/is oxidised itself

what is redox?

when oxidation and reduction occur simultaneously

define oxidation state

• degree of oxidation/reduction of an atom/element

• in a compound, normally hypothetical charge on an atom if bonding was completely ionic

what are the rules of oxidation states (general)?

• oxidation state of a simple ion is its charge

• oxidation states of all elements of a compound total 0; in a molecular ion it is the charge

• max oxidation state of an element is the group number

• min oxidation state is the group number -8

• oxidation number of a sole element is 0

• g1/g2 elements are always +1/+2

• d block elements have same oxidation state as ion charge, but the charges can vary

what are the rules of oxidation states (specific)?

• oxidation number of oxygen is -2 except in peroxides where it is -1 (H2O2) and OF2 where it is +2

• hydrogen is always +1 except in hydrides (metal H) where it is -1

what does it mean if oxidation state increases in a reaction?

has been oxidised (opposite for reduced)

how can oxidation state be used in the species?

• roman numerals after species it refers to

• mainly for p and d block as have multiple charges

what is disproportionation?

when the same element is oxidised and reduced in the equation

what are the steps for balancing a redox equation using half equations?

• do each step 2x- 1 for ox, 1 for red

• work out fomulae of species before and after the reaction and balance

• work out oxidation state of the elements before and after

• add electrons to one side to balance oxidation states

• add H+ ions to one side to balance the charges

• add H2O molecules to balance H/O

• multiply both equations to same number of electrons then set equal and electrons should cancel

what can alcohols be oxidised to?

aldehydes, ketones, carboxylic acids

what can organic products be reduced by?

LiAlH4

what is oxidation in organic compounds also?

• loss of H

• reduction is gain of H

how do you write oxidation half equations for organics?

• use [O] to represent the oxidising agent

• use H2O on the other side to account for hydrogen atoms removed

• balance

how do you write reduction half equations for organics?

• use [H] to represent the reducing agent

• if O2 atoms are removed, H2O is added as the product and the [H] is balanced