State symbols — AQA GCSE Chemistry
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State symbols explained
State symbols record the physical state of each substance in a chemical equation.
Read the full explanation
Solid is (s), liquid is (l), gas is (g) and aqueous, meaning dissolved in water, is (aq). They are written immediately after the chemical formula, for example 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g). State symbols are added after balancing, because changing a formula to show a state must not change the formula itself. They help chemists check that the equation matches the reaction described, such as a gas being produced or a precipitate forming. Aqueous does not mean liquid water: it means a substance dissolved in water, so an ionic compound in solution is shown as (aq) even though the solution is a liquid.
Your focus
- Write the correct state symbol for a solid, liquid, gas or aqueous solution.
- Place state symbols correctly within a balanced chemical equation.
- Distinguish between (l) for pure liquid water and (aq) for a substance dissolved in water.
State symbols exam tips
Marking Points
- Use (s) for solid, (l) for liquid, (g) for gas and (aq) for aqueous solution.
- Place the state symbol immediately after the chemical formula it describes.
- Use (aq) for a substance dissolved in water, not for pure liquid water, which is (l).
- Check that state symbols are consistent with the reaction described, such as a gas product or a precipitate.
- Keep the chemical formula unchanged when adding state symbols.
Examiner Tips
- 💡Add state symbols after balancing the equation so the formulae are already correct.
- 💡Check each symbol against the reaction context, especially whether a product is a gas or a precipitate.
- 💡Remember that (aq) means dissolved in water, so it applies to solutions rather than to pure liquids.
Common Mistakes
- Writing (aq) for pure water; correct this by using (l) for liquid water and (aq) only for a substance dissolved in water.
- Placing the state symbol before the formula or inside it; correct this by writing it immediately after the formula.
- Changing a subscript while adding a state symbol; correct this by leaving the formula exactly as it was and adding the symbol after it.