AQA GCSE Combined Science (8464), Higher tier · Chemistry › Bonding, structure, and the properties of matter › How bonding and structure are related to the properties of
Practise State symbols. 11 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
The four state symbols, (s), (l), (g) and (aq), and how to add them to equations. They are usually worth 1 or 2 marks in equation questions anywhere on either paper, and you should include them whenever a question asks for them.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Recall the four state symbols(s) solid, (l) liquid, (g) gas, (aq) aqueous: dissolved in water.
4
Know that aqueous means dissolved in waterAny solution in water, such as sodium chloride solution or dilute hydrochloric acid, is (aq).
5
Add state symbols to a simple equationFor example, Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g).
6
Tell (l) apart from (aq)Water itself and molten substances are (l); substances dissolved in water are (aq).
7
Use data and observations to choose state symbolsUse melting and boiling points, or words such as 'bubbles', 'precipitate' and 'solution', to decide each state.
Notes
The four state symbols
(s) solid
(l) liquid: a pure liquid or a molten (melted) substance
(g) gas
(aq) aqueous: dissolved in water (a solution in water)
Write the symbol in brackets straight after the formula, e.g. CO2(g), and give one to every reactant and product.
Choosing the right symbol
Metals, and oxides and carbonates added as powders or lumps, are solids: Mg(s), CuO(s), CaCO3(s).
Acids and alkalis used in the lab are solutions: HCl(aq), H2SO4(aq), NaOH(aq).
Water made in a reaction is (l), never (aq): water cannot be dissolved in itself.
Gases given off, e.g. H2(g), O2(g), CO2(g), Cl2(g).
A precipitate (an insoluble solid that forms when solutions are mixed) is (s). A soluble salt that stays dissolved is (aq).
A molten ionic compound is (l), e.g. molten lead bromide is PbBr2(l).
If you are given melting and boiling points, use them to decide the state at the temperature of the reaction.
Examples
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
CaCO3(s) → CaO(s) + CO2(g)
2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
Ionic equations use them too: H+(aq) + OH−(aq) → H2O(l)
Cheatsheet
(s) solid (l) liquid (g) gas (aq) aqueous = dissolved in water
Water made in a reaction: H2O(l)
Dilute acids and alkalis: (aq)
Metals and insoluble compounds: (s); a precipitate is (s)
Molten substance: (l)
Neutralisation: H+(aq) + OH−(aq) → H2O(l)
How to answer each type of question
Give the meaning of a state symbol
1 mark3
(s) solid, (l) liquid, (g) gas.
For (aq), explain it: 'dissolved in water'.
Example. NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l) What does the state symbol (aq) mean?
Show the model answer
Dissolved in water / in aqueous solution (1)
Add state symbols to an equation
1 to 2 marks5
Go through the formulae one at a time.
Ask: is it a solid, a pure liquid, a gas, or dissolved in water?
Use clues in the question: 'solution', 'bubbles', 'precipitate', 'molten'.
Check that water on its own is (l).
Example. Zinc reacts with dilute sulfuric acid. The zinc sulfate formed stays dissolved and bubbles of hydrogen are given off. Complete the equation by adding state symbols. Zn(....) + H2SO4(....) → ZnSO4(....) + H2(....)
Show the model answer
Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g) All four correct (2); two or three correct (1)
Write a balanced equation with state symbols
2 marks6
Write the correct formulae and balance the equation.
Add a state symbol to every substance, using the description in the question.
Example. When solutions of barium chloride, BaCl2, and sodium sulfate, Na2SO4, are mixed, a white precipitate of barium sulfate, BaSO4, forms. Sodium chloride stays in solution. Write a balanced equation for this reaction, including state symbols.
Compare it with each substance's melting and boiling points.
Give the symbol and the reason for each.
Example. Sulfur melts at 115 °C and boils at 445 °C. Sulfur dioxide boils at −10 °C. Sulfur reacts with oxygen at 250 °C: S + O2 → SO2 Give the state symbols for sulfur and for sulfur dioxide at 250 °C.
Show the model answer
S(l), because 250 °C is between its melting and boiling points (1) SO2(g), because 250 °C is above its boiling point (1)
Shortcuts and memory tricks
Aq sounds like aqua (water): aqueous means dissolved in water.
Bubbles or fizzing → a (g) product. Precipitate → (s). Solution → (aq).
Water is (l) in these equations, not (aq).
Where marks are lost
Writing H2O(aq). Water is (l).
Using (l) for a solution, e.g. HCl(l) for hydrochloric acid. Hydrochloric acid is a solution, so it is (aq); (l) is only for pure liquids and molten substances.
Giving a precipitate (aq). A solid that forms in a solution is (s).
Leaving out state symbols when the question asks for them: you can lose the mark even if the equation is balanced.
Exam technique
Add state symbols whenever a question asks for them, and check each one against the information given.
Read the question for clues about states: 'molten', 'solution', 'gas given off', 'white precipitate'.
Write the symbols in lower case, in round brackets, straight after each formula.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
State symbols show the states of the substances in a chemical equation. What does the state symbol (aq) mean?
aqueous: dissolved in water
Calcium carbonate decomposes when heated to form calcium oxide and carbon dioxide. Add state symbols to the equation. CaCO3(....) → CaO(....) + CO2(....)
CaCO3(s) → CaO(s) + CO2(g)
Methane burns in a gas cooker flame. CH4 + 2O2 → CO2 + 2H2O In the flame, the water is produced as a gas. Add state symbols to the equation.
CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
When solutions of silver nitrate and potassium iodide are mixed, a yellow precipitate of silver iodide, AgI, forms. Write the ionic equation for this reaction, including state symbols.
Ag+(aq) + I−(aq) → AgI(s)
Write a balanced symbol equation for this reaction, including state symbols.
Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g)
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
State symbols show the states of the substances in a chemical equation.
(a) What does the state symbol (aq) mean?[1]
(b) Give the state symbol for water at room temperature.[1]
(c) Complete the state symbols in the equation for the reaction of magnesium with hydrochloric acid. Mg(s) + 2HCl(....) → MgCl2(....) + H2(....)[2]
Show the answer and mark scheme
(a)Answer: aqueous: dissolved in water
aqueous / dissolved in water
(b)Answer: (l)
(l)
(c)Answer: HCl(aq), MgCl2(aq), H2(g)
HCl(aq) and MgCl2(aq)
H2(g)
Question 2Medium6 marks
Chemical equations should include state symbols.
(a) Calcium carbonate decomposes when heated to form calcium oxide and carbon dioxide. Add state symbols to the equation. CaCO3(....) → CaO(....) + CO2(....)[1]
(b) Add state symbols to the equation for the reaction of sodium with water. 2Na(....) + 2H2O(....) → 2NaOH(....) + H2(....)[2]
(c) When solutions of barium chloride and sodium sulfate are mixed, a white precipitate of barium sulfate forms. Add state symbols to the equation. BaCl2(....) + Na2SO4(....) → BaSO4(....) + 2NaCl(....)[2]
(d) In the electrolysis of molten sodium chloride, the sodium chloride is shown as NaCl(l), not NaCl(aq). Explain why.[1]
(d)Answer: Molten means melted (a pure liquid); it is not dissolved in water.
molten means melted / liquid, not dissolved in water
Question 3Hard7 marks
This question is about state symbols in equations.
(a) Write a balanced symbol equation, including state symbols, for the reaction of lithium with water. Lithium hydroxide is soluble in water.[3]
(b) A student wrote the state symbol for the sodium chloride in salt water as NaCl(l). Explain why this is wrong.[2]
(c) When solutions of silver nitrate and potassium iodide are mixed, a yellow precipitate of silver iodide, AgI, forms. Write the ionic equation for this reaction, including state symbols.[2]
Show the answer and mark scheme
(a)Answer: 2Li(s) + 2H2O(l) → 2LiOH(aq) + H2(g)
correct formulae: Li + H2O → LiOH + H2
balanced: 2Li + 2H2O → 2LiOH + H2
state symbols: (s), (l), (aq), (g)
(b)Answer: The sodium chloride is dissolved in water, so it should be (aq); (l) would mean molten sodium chloride, which only exists above 801 °C.
sodium chloride is dissolved in water so it should be (aq)
(l) means molten / pure liquid sodium chloride (which only exists at very high temperatures)