IGCSE Chemistry (9–1) 0971 · Topic 3

Stoichiometry: past paper questions

169 real questionsasked in 10 of the last 10 exam series2019–2026usually: Calculate, Complete, Use, Deduce, Explain

Real questions on stoichiometry

The newest 20 of 110 written questions, plus 59 multiple-choice. Open one to see it on the real paper.

0971/32 · May/June 2026 · Q6e[2]
(e) Nickel(II) hydroxide has the formula Ni(OH),. Complete Table 6.1 to calculate the relative formula mass of Ni(OH),. Table 6.1 type of atom number of atoms | relative atomic mass nickel 1 59 1x 59 =59 oxygen 16 hydrogen 1 relative formula MASS .......... [2]
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0971/32 · May/June 2026 · Q7c[1]
(c) Potassium reacts with iodine to produce potassium iodide. 13.2g of potassium reacts with excess iodine to produce 56.2g of potassium iodide. Calculate the mass of potassium iodide produced when 6.6g of potassium reacts with excess iodine. MASS = oooe.eeeeeceeeteereetteteteeeees Q [1]
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0971/42 · May/June 2026 · Q3d(iii)[1]
(iii) Solution B is formed when solution A is evaporated until 20 cm? remains. Calculate the mass of ZnSO, that is formed from solution B. MASS = ooo. eects Q [1]
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0971/32 · October/November 2025 · Q4c[2]
A different molecule found in plants has the molecular formula C 10 H 16 O 2 . Complete Table 4.1 to calculate the relative molecular mass of C 10 H 16 O 2 . Table 4.1 type of atom number of atoms relative atomic mass carbon 10 12 hydrogen 1 oxygen 16 10 × 12 = 120 relative molecular mass =
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0971/32 · October/November 2025 · Q8a[1]
Use Fig. 8.1 to determine the total volume of H 2 S produced when the reaction is complete. total volume of H 2 S = cm 3
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0971/42 · October/November 2025 · Q3b[2]
mass = g (b) Calculate the mass of solid BaCl 2 dissolved in step 1.
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0971/42 · October/November 2025 · Q3c[1]
The concentration of Na 2 SO 4 (aq) in step 2 is 1.25 mol / dm 3 . Calculate the volume, in cm 3 , of 1.25 mol / dm 3 Na 2 SO 4 (aq) added in step 2 which contains 0.100 moles of Na 2 SO 4 . volume = cm 3
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0971/62 · October/November 2025 · Q1b(iii)[2]
After washing the residue, the student dries the residue in an oven. The student then measures the mass of the dry residue. The masses the student records are shown in Table 1.1. Table 1.1 mass of small pieces of eggshell / g 2.00 mass of dry residue after filtration / g 0.11 Use the data in Table 1.1 to calculate the...
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0971/31 · May/June 2025 · Q2a(ii)[1]
The total mass of compounds formed from 1000 cm 3 of sea water is 19.0 g. Calculate the total mass of compounds formed from 1750 cm 3 of sea water. mass = g
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0971/31 · May/June 2025 · Q3c[1]
A compound of sulfur has the formula Al 2 (SO 4 ) 3 . Complete Table 3.2 to calculate the relative formula mass of Al 2 (SO 4 ) 3 . Table 3.2 atom oxygen number of atoms relative atomic mass 12 16 aluminium 27 sulfur 32 12 × 16 = 192
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0971/31 · May/June 2025 · Q4e(i)[1]
Deduce the molecular formula of this molecule.
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0971/32 · May/June 2025 · Q3c[1]
A compound of phosphorus has the formula Ca 3 (PO 4 ) 2 . Complete Table 3.2 to calculate the relative formula mass of Ca 3 (PO 4 ) 2 . Table 3.2 atom number of atoms relative atomic mass oxygen 8 16 calcium 40 phosphorus 31 8 × 16 = 128
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0971/41 · May/June 2025 · Q4c(i)[1]
Balance the symbol equation for this reaction.
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0971/41 · May/June 2025 · Q4d[3]
Ammonia is converted into ammonium sulfate, (NH 4 ) 2 SO 4 . 2NH 3 (g) + H 2 SO 4 (aq) (NH 4 ) 2 SO 4 (s) 360 dm 3 of ammonia gas, measured at r.t.p., reacts with excess sulfuric acid. Calculate the mass of ammonium sulfate produced, using the following steps. • Calculate the number of moles of NH 3 (g) in 360 dm 3 . O...
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0971/41 · May/June 2025 · Q5e[2]
An organic compound has the following composition by mass: C, 64.87%; H, 13.51%; O, 21.62%. Calculate the empirical formula of the compound. empirical formula =
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0971/42 · May/June 2025 · Q4c(iii)[3]
When (NH 4 ) 2 Cr 2 O 7 is heated the following reaction occurs. (NH 4 ) 2 Cr 2 O 7 Cr 2 O 3 + 4H 2 O + N 2 Calculate the volume of nitrogen gas produced at r.t.p., in cm 3 , when 1.26 g of (NH 4 ) 2 Cr 2 O 7 is heated using the following steps. The M r of (NH 4 ) 2 Cr 2 O 7 is 252. • Calculate the number of moles of (...
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0971/42 · May/June 2025 · Q6e(iv)[1]
Explain why 1 mol of compound B reacts with 2 mol of sodium hydroxide, NaOH.
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0971/42 · May/June 2025 · Q6e(v)[2]
Calculate the volume, in cm 3 , of 0.250 mol / dm 3 NaOH that reacts with 0.100 mol of compound B. volume = cm 3
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0971/32 · October/November 2024 · Q4b[2]
Compound A reacts with ethanol to produce a compound with the molecular formula C 8 H 14 O 5 . Complete Table 4.1 to calculate the relative molecular mass of C 8 H 14 O 5 . number of atoms relative atomic mass carbon 8 12 hydrogen 1 oxygen 16 8 × 12 = 96 relative molecular mass = type of atom Table 4.1
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0971/32 · October/November 2024 · Q7a(i)[1]
State the meaning of the state symbol (aq).
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What examiners said

Candidates should be reminded to give all numerical answers in the decimal format. Some calculators produce answers as fractions e.g. 133/4 which are not accepted.
— Examiner report, May/June 2025, 0971/31 Q2(a)(ii) (Cambridge)

The use of a formula with brackets caused significant confusion. Many candidates did not know what they represented and frequently multiplied all the numbers together. Some candidates confused atomic mass and atomic number. The contribution of aluminium atoms to the relative mass was often correct.
— Examiner report, May/June 2025, 0971/31 Q3(c) (Cambridge)

This was answered very well. The most common error was an incorrect number of oxygen molecules.
— Examiner report, May/June 2025, 0971/41 Q4(c)(i) (Cambridge)

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In the syllabus

3.1 Formulae

State the formulae of the elements and compounds named in the subject content
Define the molecular formula of a compound as the number and type of different atoms in one molecule
Deduce the formula of a simple compound from the relative numbers of atoms present in a model or a diagrammatic representation
Construct word equations and symbol equations to show how reactants form products, including state symbols
Define the empirical formula of a compound as the simplest whole number ratio of the different atoms or ions in a compound
Deduce the formula of an ionic compound from the relative numbers of the ions present in a model or a diagrammatic representation or from the charges on the ions
Construct symbol equations with state symbols, including ionic equations
Deduce the symbol equation with state symbols for a chemical reaction, given relevant information

3.2 Relative masses of atoms and molecules

Describe relative atomic mass, Ar, as the average mass of the isotopes of an element compared to 1/12th of the mass of an atom of 12C
Define relative molecular mass, Mr, as the sum of the relative atomic masses. Relative formula mass, Mr, will be used for ionic compounds
Calculate reacting masses in simple proportions. Calculations will not involve the mole concept

3.3 The mole and the Avogadro constant

State that concentration can be measured in g / dm3 or mol / dm3
State that the mole, mol, is the unit of amount of substance and that one mole contains 6.02 × 1023 particles, e.g. atoms, ions, molecules; this number is the Avogadro constant
Use the relationship mass (g) amount of substance (mol) = molar mass (g / mol) to calculate: (a) amount of substance (b) mass (c) molar mass (d) relative atomic mass or relative molecular / formula mass (e) number of particles, using the value of the Avogadro constant
Use the molar gas volume, taken as 24 dm3 at room temperature and pressure, r.t.p., in calculations involving gases
Calculate stoichiometric reacting masses, limiting reactants, volumes of gases at r.t.p., volumes of solutions and concentrations of solutions expressed in g / dm3 and mol / dm3, including conversion between cm3 and dm3
Use experimental data from a titration to calculate the moles of solute, or the concentration or volume of a solution
Calculate empirical formulae and molecular formulae, given appropriate data
Calculate percentage yield, percentage composition by mass and percentage purity, given appropriate data

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