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Half Equations from Ionic Equations

Half equations can be derived from net ionic equations.for example3Cu(s) + 8H+(aq) + 2NO3-(aq) → 3Cu2+ (aq) + 2NO(g) + 4H2O(l)The ionic half equations are:3Cu(s) → 3Cu2+ (aq)8H+(aq) + 2NO3-(aq) → 2NO(g) + 4H2O(l)Adding the electrons:3Cu(s) → 3Cu2+ (aq) +6e-8H+(aq) + 2NO3-(aq) +6e-→ 2NO(g) + 4H2O(l)
Four steps1. Write any ionic compounds as ions.2. Identify and remove the spectator ions to get the net ionic equation.3. Separate the net ionic equation into two ionic half equations.4. Add the same number of electrons to the two ionic half equations.

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Specification: AQA Chemistry (7404), AS-level, 3.1.7 Oxidation, reduction and redox equations. Topic: Oxidation and Reduction.

Key terms in this lesson

Spectator ion
An ion that is present in a reaction mixture but takes no part in the reaction, remaining unchanged.
Ionic equation
An equation that shows only the particles that react, leaving out spectator ions.
Half equation
An equation that shows only the oxidation or only the reduction part of a redox reaction, including the electrons transferred.

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