Topic 3 Redox reactions

The charge that an ion has or the charge that it would have if the species were fully ionic.

Oxidation results in an increase in oxidation number.

Reduction results in a decrease in oxidation number.

An element in its elemental form is always zero (O2, N2, Fe, Na).

The sum of the oxidation numbers is a neutral compound must equal zero (NH3).

The sum of the oxidation numbers in an ion must equal the charge on the ion.

The more electronegative element is given the negative oxidation number (NH3, CH4).

The oxidation number of hydrogen is nearly always +1 except in hydrides when it -1

The oxidation number of oxygen is nearly always -2 except in peroxides when its -1 and when in a compound with fluorine its positive.

The oxidation number of fluorine is always -1

Mg —> Mg2+ + 2e

Cl2 + 2e —> 2Cl-

A simultaneous occurrence of oxidation and reduction of the same element in a single reaction.

A species that oxidises another species by removing one or more (of their) electrons. When an oxidising agent reacts it gains electrons and is therefore reduced.

A species that reduces another species by adding one or more electrons. When a reducing agent reacts it loses electrons and is therefore oxidised.

When an element has more than one oxidation state, the name often includes the oxidation number of the element written as a Roman numeral in brackets.

• Use oxidation numbers to balance • Now balance the H and O atoms • Lastly balance the charges (WHE on the equation) The equation is now balanced.