Chemistry › Practise › Questions › Formulae, equations and state symbols

Questions on formulae, equations and state symbols

Formulae of ionic compounds from the charges on common ions, including polyatomic ions and brackets, the diatomic elements, balancing equations by inspection, the four state symbols and the meaning of (aq), the solubility rules for deciding what precipitates, state symbols from observations, hydrated salts and water of crystallisation, ionic equations and spectator ions, the formulae of common acids, alkalis and their salts, ionic equations for acids with carbonates, and half-equations as a preview of redox.

20 original questions · 66 marks · the formulae, equations and state symbols notes · Working in the laboratory · Flashcards for this unit

To print: the questions (PDF, 81 KB) · the mark schemes (PDF, 87 KB)

How to use this page

• Every question here is written for this library rather than taken from a past paper. Write your answer out before opening a mark scheme: the schemes award marks point by point, and the points are much easier to see when you have something of your own to compare against.
• The player marks nothing for you. It shows one question, waits, then shows the scheme so you can mark yourself, and brings a question back sooner when it went badly.
• Each line of a scheme is one mark: B1 is a point that stands on its own, M1 a method mark, and A1 the answer or an accuracy point. A six-mark question marked by level lists what a full answer covers, then says which level an answer reaches.
• Each question’s code is the one printed in the workbook. Type inklearning.co.uk/q/ and a code to jump to its question.
• The PDF links above print the same questions, with the answers in a separate book.
• As a rough guide, allow about 1.4 minutes a mark; each board’s papers run at their own pace.

Question codes are permanent, so the numbers on this page can skip or run out of order; nothing is missing.

• 6 marks · Explain · FE-Q14

  Explain what is seen when dilute hydrochloric acid is added in turn to solid magnesium oxide, to solid magnesium carbonate and to sodium hydroxide solution, and what the full and ionic equations show about what reacts.

  Mark scheme

  Indicative content

  1. magnesium oxide dissolves to give a colourless solution with no gas: MgO(s) + 2HCl(aq) → MgCl₂(aq) + H₂O(l)
  2. the oxide is an insoluble solid, so it stays whole in the ionic equation, MgO(s) + 2H⁺(aq) → Mg²⁺(aq) + H₂O(l)
  3. magnesium carbonate fizzes and dissolves: MgCO₃(s) + 2HCl(aq) → MgCl₂(aq) + H₂O(l) + CO₂(g), the gas giving the fizz
  4. the carbonate is insoluble, so its ionic equation keeps it whole: MgCO₃(s) + 2H⁺(aq) → Mg²⁺(aq) + H₂O(l) + CO₂(g)
  5. sodium hydroxide shows no visible change, only warming, because both reactants and products are in solution: NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
  6. its ionic equation is H⁺(aq) + OH⁻(aq) → H₂O(l); in all three reactions H⁺ is what reacts and chloride is a spectator

  Levels

  • Level 3 (5–6 marks) all three observations are given and matched to what the full equations show, all three ionic equations are correct with the insoluble solids kept whole, and the answer draws the common conclusion that H⁺ reacts in every case and chloride is a spectator
  • Level 2 (3–4 marks) the observations and full equations are right; one ionic equation splits the oxide or carbonate into ions, or the spectator conclusion is not drawn
  • Level 1 (1–2 marks) fizzing with the carbonate is noted, with one equation; magnesium oxide is commonly written as separate Mg²⁺ and O²⁻ ions, and chloride is kept in the ionic equations

• 4 marks · Complete · FE-Q3

  Complete and balance these two equations, adding the state symbols that are missing: the complete combustion of propane, C₃H₈(g) + O₂ → CO₂ + H₂O, and the reduction of iron(III) oxide in a blast furnace, Fe₂O₃(s) + CO(g) → Fe(l) + CO₂(g).

  Mark scheme

  1. B1 C₃H₈ + 5O₂ → 3CO₂ + 4H₂O, with the coefficients 5, 3 and 4; allow multiples
  2. B1 state symbols (g) for oxygen and carbon dioxide and (l) for water; allow H₂O(g)
  3. B1 Fe₂O₃(s) + 3CO(g) → 2Fe(l) + 3CO₂(g)
  4. B1 2 iron atoms, 3 carbon atoms and 6 oxygen atoms on each side of the iron equation

• 4 marks · Explain · FE-Q4

  Explain why a student who balances the equation for hydrogen burning in oxygen as H₂(g) + O₂(g) → H₂O₂(l) is wrong, and give the correct balanced equation with state symbols.

  Mark scheme

  1. B1 the subscripts are part of a formula and fix which substance it represents
  2. B1 H₂O₂ is hydrogen peroxide, which the reaction does not produce; the product is water
  3. B1 the equation is balanced with coefficients only: 2H₂ + O₂ → 2H₂O
  4. B1 2H₂(g) + O₂(g) → 2H₂O(l), with state symbols; allow H₂O(g)

• 4 marks · State · FE-Q5

  State the four state symbols used in equations, and explain why ethanol in water is written C₂H₅OH(aq) but water itself is always H₂O(l).

  Mark scheme

  1. B1 (s) means solid and (l) means liquid
  2. B1 (g) means gas and (aq) means dissolved in water
  3. B1 (aq) is different from (l): pure ethanol is C₂H₅OH(l), and only ethanol dissolved in water is (aq)
  4. B1 water cannot be dissolved in water, so as a pure liquid it is always (l); reject H₂O(aq)

• 4 marks · Suggest · FE-Q8

  Suggest why the enthalpy change of neutralisation is almost the same for hydrochloric acid with sodium hydroxide as for nitric acid with potassium hydroxide, but slightly less exothermic for ethanoic acid with sodium hydroxide.

  Mark scheme

  1. B1 the ionic equation for both strong-acid reactions is H⁺(aq) + OH⁻(aq) → H₂O(l)
  2. B1 the other ions are spectators, so the same chemical change happens in both and releases the same energy per mole of water
  3. B1 ethanoic acid is weak and mostly un-ionised, so it stays whole: CH₃COOH(aq) + OH⁻(aq) → CH₃COO⁻(aq) + H₂O(l)
  4. B1 that is a different reaction, in which some energy goes into ionising the acid, so less energy is released overall

• 4 marks · Compare · FE-Q10

  Compare what happens, and the equations, when barium chloride solution is mixed with sodium sulfate solution and when barium nitrate solution is mixed with potassium sulfate solution.

  Mark scheme

  1. B1 both mixtures give a white precipitate of barium sulfate
  2. B1 both ionic equations are Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)
  3. B1 the full equations differ only in the spectator ions, Na⁺ and Cl⁻ in one and K⁺ and NO₃⁻ in the other
  4. B1 any soluble barium salt with any soluble sulfate is the same reaction, which is the basis of the sulfate test

• 4 marks · Give · FE-Q13

  Give the two half-equations, with state symbols, for zinc powder becoming coated with silver in silver nitrate solution, and combine them into the ionic equation, showing how the electrons are balanced.

  Mark scheme

  1. B1 Zn(s) → Zn²⁺(aq) + 2e⁻
  2. B1 Ag⁺(aq) + e⁻ → Ag(s)
  3. B1 the silver half-equation is doubled so that two electrons are gained for the two that zinc loses
  4. B1 Zn(s) + 2Ag⁺(aq) → Zn²⁺(aq) + 2Ag(s), with the electrons cancelled; ignore nitrate shown on both sides

• 3 marks · Give · FE-Q1

  Give the formulae of calcium hydroxide, aluminium sulfate and ammonium carbonate.

  Mark scheme

  1. B1 calcium hydroxide is Ca(OH)₂; reject CaOH₂
  2. B1 aluminium sulfate is Al₂(SO₄)₃
  3. B1 ammonium carbonate is (NH₄)₂CO₃

• 3 marks · Explain · FE-Q6

  Explain why sodium ions and chloride ions do not appear in the ionic equation for the reaction of barium chloride solution with sodium sulfate solution.

  Mark scheme

  1. B1 sodium chloride is soluble, so the sodium and chloride ions stay dissolved after mixing
  2. B1 they are present on both sides of the equation unchanged, so they are spectator ions
  3. B1 spectator ions are cancelled, leaving Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)

• 3 marks · Give · FE-Q7

  Give the ionic equation, with state symbols, for the reaction of silver nitrate solution with potassium bromide solution, and name the spectator ions.

  Mark scheme

  1. B1 Ag⁺ + Br⁻ → AgBr, with the species in the right places
  2. B1 state symbols Ag⁺(aq), Br⁻(aq) and AgBr(s)
  3. B1 the spectator ions are the potassium ion, K⁺, and the nitrate ion, NO₃⁻

• 3 marks · Suggest · FE-Q9

  Suggest the identity of the yellow precipitate formed when lead(II) nitrate solution is mixed with potassium iodide solution, and give the ionic equation for its formation.

  Mark scheme

  1. B1 potassium salts and nitrates are always soluble, so the precipitate must be lead(II) iodide
  2. B1 lead(II) iodide has the formula PbI₂, because Pb²⁺ needs two I⁻ ions
  3. B1 Pb²⁺(aq) + 2I⁻(aq) → PbI₂(s); state symbols required

• 3 marks · Describe · FE-Q11

  Describe how an ionic equation is written from a balanced full equation with state symbols.

  Mark scheme

  1. B1 split every aqueous ionic compound and strong acid into its ions, keeping the coefficients
  2. B1 leave solids, liquids, gases and covalent molecules whole
  3. B1 cancel ions that appear unchanged on both sides, then check that atoms and total charge balance

• 3 marks · Evaluate · FE-Q16

  Evaluate a student's ionic equation for magnesium with hydrochloric acid: Mg(s) + 2H⁺(aq) + 2Cl⁻(aq) → Mg²⁺(aq) + 2Cl⁻(aq) + H₂(g).

  Mark scheme

  1. B1 the equation is balanced in atoms and in charge, and the state symbols are correct
  2. B1 it is not a complete ionic equation, because Cl⁻(aq) appears unchanged on both sides and is a spectator
  3. B1 cancelling it gives Mg(s) + 2H⁺(aq) → Mg²⁺(aq) + H₂(g)

• 3 marks · Explain · FE-Q18

  Explain why the formula of iron(III) sulfate is Fe₂(SO₄)₃.

  Mark scheme

  1. B1 the Roman numeral shows the iron ion is Fe³⁺, and sulfate is SO₄²⁻
  2. B1 two Fe³⁺ ions give 6+ and three SO₄²⁻ ions give 6−, the lowest whole numbers for which the charges cancel
  3. B1 more than one sulfate ion is needed, so the sulfate is written in brackets with the 3 outside

• 3 marks · Give · FE-Q19

  Give the formulae of potassium sulfate, ammonium nitrate and sodium ethanoate.

  Mark scheme

  1. B1 potassium sulfate is K₂SO₄
  2. B1 ammonium nitrate is NH₄NO₃
  3. B1 sodium ethanoate is CH₃COONa; allow CH₃CO₂Na

• 3 marks · Explain · FE-Q20

  Explain why the ionic equation for hydrochloric acid with sodium carbonate solution contains CO₃²⁻(aq), but the ionic equation for hydrochloric acid with calcium carbonate contains CaCO₃(s).

  Mark scheme

  1. B1 sodium carbonate is soluble, so in solution it is split into Na⁺(aq) and CO₃²⁻(aq), and Na⁺ cancels as a spectator, giving CO₃²⁻(aq) + 2H⁺(aq) → H₂O(l) + CO₂(g)
  2. B1 calcium carbonate is an insoluble solid, so it has no free ions in solution and is left whole
  3. B1 its calcium ions appear as a product: CaCO₃(s) + 2H⁺(aq) → Ca²⁺(aq) + H₂O(l) + CO₂(g)

• 3 marks · Suggest · FE-Q21

  Suggest the identity of the pale blue solid that forms when sodium hydroxide solution is added to blue copper(II) sulfate solution, and give the ionic equation, with state symbols, for its formation.

  Mark scheme

  1. B1 sodium salts are soluble, so the solid must be copper(II) hydroxide, a precipitate
  2. B1 its formula is Cu(OH)₂, because Cu²⁺ needs two OH⁻ ions
  3. B1 Cu²⁺(aq) + 2OH⁻(aq) → Cu(OH)₂(s)

• 2 marks · Give · FE-Q2

  Give the formulae of the seven elements that exist as diatomic molecules at room temperature.

  Mark scheme

  1. B1 hydrogen H₂, nitrogen N₂ and oxygen O₂
  2. B1 the halogens F₂, Cl₂, Br₂ and I₂

• 2 marks · Identify · FE-Q15

  Identify the precipitate formed when calcium nitrate solution is mixed with sodium carbonate solution, and give its ionic equation.

  Mark scheme

  1. B1 calcium carbonate, because carbonates other than those of Group 1 and ammonium are insoluble
  2. B1 Ca²⁺(aq) + CO₃²⁻(aq) → CaCO₃(s)

• 2 marks · Explain · FE-Q22

  Explain what the formula CuSO₄·5H₂O shows, and why the crystals turn white when heated.

  Mark scheme

  1. B1 the crystals hold five molecules of water of crystallisation for each CuSO₄, joined to the formula by the raised dot
  2. B1 heating drives the water off as steam, leaving white anhydrous CuSO₄: CuSO₄·5H₂O(s) → CuSO₄(s) + 5H₂O(g)

Practise formulae, equations and state symbols one question at a time