Half Equations & Ionic Equations (AQA GCSE Chemistry): Revision Notes
📚 Revision Notes
1.1.4 Half Equations & Ionic Equations
Half Equations
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Half equations are used to represent the oxidation or reduction processes in a redox reaction. They show how electrons are transferred during these reactions.
In a half equation:
- Oxidation is the loss of electrons.
- Reduction is the gain of electrons. Example of Oxidation:
When sodium (Na) loses an electron to form a sodium ion (Na⁺):
Example of Reduction:
When chlorine (Cl₂) gains electrons to form chloride ions (Cl⁻):
Balancing Half Equations:
- It is important to ensure that the number of electrons lost in the oxidation half equation equals the number of electrons gained in the reduction half equation.
- This allows for the correct combination of half equations to form a full ionic equation.
Ionic Equations
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Ionic equations show only the species that are directly involved in the chemical reaction. Spectator ions, which do not change during the reaction, are omitted.
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Steps to Write an Ionic Equation:
- Write the balanced chemical equation for the reaction.
- Separate the aqueous compounds into their respective ions.
- Identify and remove the spectator ions (ions that appear unchanged on both sides of the equation).
- Write the remaining ions that are involved in the reaction, forming the ionic equation.
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Example:
- Consider the reaction between silver nitrate (AgNO₃) and sodium chloride (NaCl) in aqueous solution:
- In ionic form:
- The spectator ions (Na⁺ and NO₃⁻) are removed, leaving the ionic equation: