State symbols — AQA GCSE Combined Science
Test yourself on State symbols with AQA GCSE practice questions.
7 days Premium · Then free forever · No card, no charge
State symbols explained
State symbols are short labels written after a chemical formula to show the physical state of each substance.
Read the full explanation
A solid is (s), a liquid is (l) and a gas is (g). An aqueous solution, meaning a substance dissolved in water, is (aq). For example, sodium chloride solution is NaCl(aq), while solid sodium chloride is NaCl(s). Water is H₂O(l) when pure, but H₂O(g) when steam. The symbol (aq) is not a fourth state of matter; it describes a solid, liquid or gas that has dissolved in water. State symbols are placed immediately after the formula, before any plus sign or arrow. They help chemists see what is present at the start and end of a reaction, and they are needed for ionic equations and for identifying precipitates.
Students should be able to include appropriate state symbols in chemical equations for the reactions in this specification.
This skill means adding (s), (l), (g) or (aq) to every formula in equations for the reactions you study. Decide the state from the substance and the conditions described. For example, burning magnesium in oxygen gives 2Mg(s) + O₂(g) → 2MgO(s). Neutralisation of hydrochloric acid by sodium hydroxide solution gives HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l). If a product is insoluble and forms a solid in solution, label it (s) as a precipitate, for example AgCl(s). Metals are usually (s) except mercury, which is (l). Gases such as O₂ and CO₂ are (g) unless dissolved, when they are (aq). Water is always (l) in aqueous reactions. Apply symbols consistently to both sides and to ionic equations.
Your focus
- Assign (s), (l), (g) or (aq) correctly to a named substance or formula.
- Insert state symbols in the correct position in a chemical equation.
- Explain the difference between a pure liquid and an aqueous solution using examples.
Show all 6 objectives
- Add correct state symbols to balanced equations for specified reactions.
- Deduce the state of a product from solubility information or reaction conditions.
- Produce ionic equations with correct state symbols for dissolved ions and precipitates.
State symbols exam tips
Marking Points
- Correctly matches (s) to solid, (l) to liquid, (g) to gas and (aq) to an aqueous solution.
- Places each state symbol immediately after the chemical formula it describes, for example HCl(aq) not (aq)HCl.
- Distinguishes an aqueous solution from a pure liquid, for example NaCl(aq) compared with H₂O(l).
- Uses (aq) for a substance dissolved in water even if that substance is normally a gas or solid, for example CO₂(aq).
- Applies state symbols consistently to every formula on both sides of an equation, including ionic equations.
- Recognises that a precipitate is shown as (s) even though it forms in solution.
- Selects the correct state symbol for each reactant and product from the reaction conditions given.
- Writes state symbols after each formula and before any + or → symbol.
- Uses (s) for insoluble precipitates formed in solution, such as AgCl(s) or BaSO₄(s).
- Uses (aq) for dissolved acids, alkalis and salts, and (l) for pure water or liquid mercury.
- Balances the equation and includes state symbols without altering the formulae or coefficients.
- Applies state symbols correctly in ionic equations, including spectator ions where required.
Examiner Tips
- 💡Read the question wording for clues such as solution, solid, gas or molten, then choose the matching symbol.
- 💡Check every formula in the equation has a state symbol if the question asks for them, including products.
- 💡For ionic equations, label each ion and compound, remembering that a precipitate is (s) and dissolved ions are (aq).
- 💡Underline or list the physical state of each substance before writing the equation to reduce errors.
- 💡Check that coefficients are balanced first, then add state symbols so the two tasks do not interfere.
- 💡For precipitation and ionic equations, decide which product is insoluble and label it (s).
Common Mistakes
- Writing (aq) for water: water is the solvent, so it is always written as H₂O(l) in aqueous reactions, never H₂O(aq).
- Putting the state symbol before the formula, such as (s)NaCl: the symbol belongs after the formula, so write NaCl(s).
- Using (aq) for a liquid metal such as mercury: mercury is Hg(l), because (aq) means dissolved in water.
- Labelling a precipitate as (aq) because it forms in water: an insoluble solid is (s), so write AgCl(s).
- Giving water (aq) in a neutralisation equation: water is the solvent, so correct it to H₂O(l).
- Omitting state symbols from one side of the equation: apply them to every formula on both sides.