Question 1Multiple choice · 1 markA* challenge
What is the formula of iron(III) sulfate?
- A FeSO4
- B Fe3(SO4)2
- C Fe2SO12
- D Fe2(SO4)3
Show answer
Answer: D
10 free IGCSE Chemistry Stoichiometry questions written in the style of Cambridge Chemistry papers: 2 multiple-choice and 8 structured, each with its answer and mark scheme. 4 of them are A* challenge questions, built to catch the mistakes strong students still make.
This topic covers Formulae & equations, Relative masses & the mole, Concentration & titration. Work through the questions below, then generate a full Stoichiometry paper with a fresh set every time.
Generate a full Stoichiometry paper →What is the formula of iron(III) sulfate?
Answer: D
What is the formula of magnesium carbonate?
Answer: D
A student adds 12.5 g of calcium carbonate to 50 cm³ of 1.0 mol/dm³ hydrochloric acid.
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
Calculate the number of moles of calcium carbonate and the number of moles of hydrochloric acid used.
Deduce which reactant is in excess. Explain your answer.
Calculate the volume of carbon dioxide, in cm³, formed at room temperature and pressure.
The solution is evaporated and 2.22 g of anhydrous calcium chloride is obtained. Calculate the percentage yield.
Suggest why the reaction becomes slower as it proceeds, in terms of particles.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 0.125 mol, 0.05 mol 12.5 ÷ 100 = 0.125 B1 1 × 50 ÷ 1000 = 0.05 B1 | 2 |
| (b) | calcium carbonate is in excess: 0.125 mol CaCO3 needs 0.25 mol HCl 0.125 mol CaCO3 reacts with 0.25 mol HCl (or 0.05 mol HCl reacts with 0.025 mol CaCO3) M1 calcium carbonate in excess A1 | 2 |
| (c) | 600 cm³ moles CO2 = 0.025 (from limiting reactant) M1 600 A1 | 2 |
| (d) | 80% Mr CaCl2 = 111 B1 theoretical mass = 2.78 g M1 80 A1 | 3 |
| (e) | Concentration of acid falls, so fewer particles per unit volume and collisions become less frequent concentration of (acid) particles decreases B1 fewer collisions per second / lower collision frequency B1 | 2 |
A solution is made by dissolving sodium hydroxide in water. (Mr NaOH = 40)
Calculate the mass of sodium hydroxide needed to make 500 cm³ of a 0.50 mol/dm³ solution.
Convert this concentration into g/dm³.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 10 g moles = 0.5 × 0.5 C1 × 40 = 10 g A1 | 2 |
| (b) | 20 g/dm³ 20 g/dm³ B1 | 1 |
25.0 cm³ of 0.200 mol/dm³ aqueous sodium hydroxide is titrated with dilute sulfuric acid. The mean titre is 23.93 cm³.
2NaOH + H2SO4 → Na2SO4 + 2H2O
Calculate the concentration of the sulfuric acid in mol/dm³.
Name a suitable indicator and give the colour change at the end-point.
A sample of hydrated sodium carbonate, Na2CO3•xH2O, of mass 2.50 g is heated until all the water is removed. The mass of the anhydrous salt is 1.14 g.
Calculate the value of x.
Describe how the student can make sure that all of the water has been removed.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 0.104 mol/dm³ moles NaOH = 0.005 M1 moles H2SO4 = 0.0025 M1 0.104 A1 | 3 |
| (b) | methyl orange: yellow to orange/red (or phenolphthalein: pink to colourless) suitable indicator B1 correct colour change for that indicator, in the right direction B1 | 2 |
| (c) | 7 mass of water = 1.36 g B1 moles water = 0.0754; moles salt = 0.0108 M1 ratio water : salt M1 7 A1 | 4 |
| (d) | Heat, cool and weigh repeatedly until the mass is constant heat to constant mass B1 weigh after cooling, repeat until two readings agree B1 | 2 |
This question is about metal carbonates.
Write the equation, with state symbols, for the thermal decomposition of zinc carbonate.
Describe a test for carbon dioxide and give the result.
Calculate the mass of zinc oxide formed when 3.13 g of zinc carbonate is heated to constant mass. [Mᵣ: ZnCO₃, 125; ZnO, 81]
Calculate the volume of carbon dioxide produced at r.t.p. when 3.13 g of zinc carbonate decomposes.
Sodium carbonate does not decompose when heated in a Bunsen flame. Suggest why, in terms of reactivity.
Explain why the student heats the carbonate to constant mass.
Zinc oxide is a basic oxide. Write the equation for its reaction with dilute nitric acid.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | ZnCO₃(s) → ZnO(s) + CO₂(g) correct formulae B1 balanced B1 state symbols B1 | 3 |
| (b) | bubble through limewater; turns milky limewater B1 turns milky / cloudy B1 | 2 |
| (c) | 2.03 g moles = 3.13/125 = 0.0250 M1 1 : 1 ratio, × 81 M1 2.03 g A1 | 3 |
| (d) | 0.601 dm³ 0.0250 × 24 = 0.601 dm³ B1 | 1 |
| (e) | carbonates of more reactive metals are more stable sodium is very reactive so its carbonate is more stable / thermal stability increases with reactivity B1 | 1 |
| (f) | to make sure decomposition is complete to ensure all the carbonate has decomposed B1 | 1 |
| (g) | ZnO + 2HNO₃ → Zn(NO₃)₂ + H₂O correct formulae B1 balanced B1 | 2 |
25.0 cm³ of sodium hydroxide solution is titrated with 0.100 mol/dm³ hydrochloric acid. The average titre is 25.00 cm³. NaOH + HCl → NaCl + H₂O
Calculate the number of moles of hydrochloric acid used.
Calculate the concentration of the sodium hydroxide in mol/dm³.
Name a suitable indicator and state the colour change at the end-point.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 0.0025 mol 0.0025 mol B1 | 1 |
| (b) | 0.1 mol/dm³ moles NaOH = 0.0025 C1 ÷ 0.0250 = 0.1 mol/dm³ A1 | 2 |
| (c) | methyl orange yellow → orange/red (or phenolphthalein pink → colourless) Any 2 of: methyl orange; yellow to orange (or phenolphthalein; pink to colourless) B2 | 2 |
Calcium carbonate decomposes on heating: CaCO₃ → CaO + CO₂. (Mr CaCO₃ = 100, CaO = 56)
Calculate the mass of calcium oxide made from 20 g of calcium carbonate.
Calculate the volume of carbon dioxide produced at r.t.p.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 11.2 g moles = 20 ÷ 100 C1 × 56 = 11.2 g A1 | 2 |
| (b) | 4.8 dm³ moles × 24 C1 4.8 dm³ A1 | 2 |
This question is about the reaction between aqueous sodium hydroxide and sulfuric acid.
Write the ionic equation for the neutralisation of an acid by an alkali.
Write the symbol equation for the reaction between sodium hydroxide and sulfuric acid.
A student titrates 25.0 cm³ of aqueous sodium hydroxide with 0.100 mol/dm³ sulfuric acid, using methyl orange indicator. Fig. 9.1 shows the burette readings at the start and end of the first (rough) titration.
Use Fig. 9.1 to find the volume of acid added in the rough titration.
Name the piece of apparatus used to measure exactly 25.0 cm³ of sodium hydroxide.
Give the colour change at the end-point.
The mean volume of acid used is 15.00 cm³. Calculate the concentration of the sodium hydroxide in mol/dm³.
Convert your answer to (c)(iv) into a concentration in g/dm³. [Mᵣ: NaOH, 40]
Explain why the student repeats the titration until two concordant results are obtained.
The student wants to make pure sodium sulfate crystals. Explain why the indicator method must be changed before evaporating the solution.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | H⁺ + OH⁻ → H₂O H⁺ + OH⁻ → H₂O B1 | 1 |
| (b) | 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O correct formulae B1 balanced B1 | 2 |
| (c)(i) | 15.40 cm³ readings 1.20 and 16.60 cm³ B1 15.40 cm³ B1 | 2 |
| (ii) | volumetric pipette (volumetric) pipette B1 | 1 |
| (iii) | yellow to orange / red yellow to orange (or red) B1 | 1 |
| (iv) | 0.120 mol/dm³ moles of acid = 0.100 × 15.00/1000 = 1.50 × 10−3 M1 moles NaOH = 2 × moles acid = 3.00 × 10−3 M1 ÷ 0.0250 = 0.120 mol/dm³ A1 | 3 |
| (v) | 4.80 g/dm³ 0.120 × 40 = 4.80 g/dm³ B1 | 1 |
| (vi) | to check reliability / identify anomalies to make sure the results are repeatable / to identify anomalous results B1 | 1 |
| (d) | repeat without indicator using the same volumes, indicator would contaminate repeat the titration with the same volumes but without the indicator B1 otherwise the crystals would be contaminated with indicator B1 | 2 |
Write balanced symbol equations for these reactions, including state symbols.
Magnesium reacts with dilute hydrochloric acid to form magnesium chloride and hydrogen.
Methane burns completely in oxygen.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g) correct formulae and balancing B1 correct state symbols B1 | 2 |
| (b) | CH₄ + 2O₂ → CO₂ + 2H₂O correct formulae B1 balanced B1 | 2 |
In the 0620 syllabus, Stoichiometry covers Formulae & equations, Relative masses & the mole, Concentration & titration.
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