IGCSE Chemistry 0620 · Stoichiometry · 3.3

The mole and the Avogadro constant: past paper questions

88 real questionsasked in 9 of the last 10 exam series2019–2026usually: Calculate, State, Suggest, Explain, Use

Real questions on the mole and the avogadro constant

The newest 20 of 88 written questions. Open one to see it on the real paper.

0620/32 · May/June 2026 · Q7c[1]
Potassium reacts with iodine to produce potassium iodide. 13.2 g of potassium reacts with excess iodine to produce 56.2 g of potassium iodide. mass = g Calculate the mass of potassium iodide produced when 6.6 g of potassium reacts with excess iodine.
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0620/41 · May/June 2026 · Q6b(i)[3]
Chromium( III ) oxide is a product of the thermal decomposition of potassium dichromate( VI ), K 2 Cr 2 O 7 . The other products are potassium chromate( VI) , K 2 CrO 4 , and oxygen, O 2 . The equation for the thermal decomposition is shown. 4K 2 Cr 2 O 7 4K 2 CrO 4 + 2Cr 2 O 3 + 3O 2 Calculate the maximum mass of Cr 2...
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0620/43 · May/June 2026 · Q4d(ii)[3]
The equation for the reaction is shown. 2KMnO 4 Calculate the mass of KMnO 4 used to produce 0.64 g of O 2 . [M r : KMnO 4 , 158; O 2 , 32] Use the following steps. • Calculate the number of moles of O 2 produced. mol • Calculate the number of moles of KMnO 4 used. mol • K 2 MnO 4 + MnO 2 + O 2 Calculate the mass of KM...
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0620/32 · February/March 2026 · Q8d[1]
Potassium reacts with iodine to produce potassium iodide. When a 5.6 g sample of potassium reacts with excess iodine, 23.8 g of potassium iodide is produced. Calculate the mass of potassium iodide produced when 2.8 g of potassium reacts with excess iodine. mass = g
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0620/33 · October/November 2025 · Q4c[2]
A different molecule found in plants has the molecular formula C 9 H 10 O 3 . Complete Table 4.1 to calculate the relative molecular mass of C 9 H 10 O 3 . Table 4.1 type of atom number of atoms relative atomic mass carbon 9 12 hydrogen 1 oxygen 16 9 × 12 = 108 relative molecular mass =
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0620/41 · October/November 2025 · Q1e[2]
Calculate the number of atoms in 2.00 g of argon. Give your answer in standard form. number of atoms =
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0620/42 · 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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0620/43 · October/November 2025 · Q4b[3]
Ethene, C 2 H 4 , reacts with chlorine, Cl 2 , to form 1,2-dichloroethane, CH 2 Cl CH 2 Cl . The equation for this reaction can be represented as shown. H C C + Cl H H Cl Cl H H C C H H Cl Table 4.2 shows some bond energies. Table 4.2 bond bond energy in kJ / mol C–C 350 C=C 610 C–H 410 Cl –Cl 240 C–Cl 340 Use the bond...
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0620/43 · October/November 2025 · Q4d(ii)[3]
Calculate the volume, in cm 3 , of CO 2 (g) that is produced at room temperature and pressure (r.t.p.) when 50.0 cm 3 of 0.100 mol / dm 3 HCl reacts with excess MgCO 3 . The volume of 1 mol of any gas is 24 000 cm 3 at r.t.p. Use the following steps. • Calculate the number of moles of HCl in 50.0 cm 3 of 0.100 mol / dm...
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0620/42 · February/March 2025 · Q1f[1]
number of particles in one mole, in standard form.
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0620/41 · October/November 2024 · Q4a(iii)[4]
Calculate the volume of NO 2 gas, at r.t.p., formed when 7.40 g of Mg(NO 3 ) 2 is heated. Use the following steps. ● Calculate the M r of Mg(NO 3 ) 2 . Calculate the number of moles of Mg(NO 3 ) 2 used. mol Determine the number of moles of NO 2 formed. mol ● Calculate the volume of NO 2 gas, in cm 3 , at r.t.p. 3 ● ●
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0620/43 · October/November 2024 · Q3a[1]
Tin( IV ) oxide has the formula SnO 2 . The relative formula mass, M r , of SnO 2 is 151. Calculate the percentage by mass of tin in SnO 2 . percentage by mass of tin in SnO 2 = %
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0620/43 · October/November 2024 · Q4f(ii)[2]
In another experiment, 48.0 cm 3 of hydrogen gas, H 2 , is produced. The experiment is carried out at room temperature and pressure, r.t.p. Calculate the number of molecules in 48.0 cm 3 of H 2 gas measured at r.t.p. The value of the Avogadro constant is 6.02 × 10 23 . molecules
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0620/61 · October/November 2024 · Q1b[1]
State what is removed from the ﬁltrate in step 3.
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0620/61 · October/November 2024 · Q1c[1]
Describe what must be done after the ﬁltrate has been heated in step 3 to obtain a larger amount of sodium sulfate crystals.
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0620/61 · October/November 2024 · Q2a[4]
Use the information in the description of the experiments and the measuring cylinder diagrams to complete Table 2.1.
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0620/61 · October/November 2024 · Q2b[5]
Complete a suitable scale on the y-axis and plot the results from Experiments 1 to 8 on Fig. 2.1. Draw two straight lines of best ﬁt through your points. The ﬁrst straight line should be for the ﬁrst ﬁve experiments and must be extended to pass through (0,0). The second straight line should be for the last three experi...
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0620/61 · October/November 2024 · Q2c[2]
Use Fig. 2.1 to deduce the level of precipitate on the measuring cylinder scale when the experiment is repeated using 2.8 cm⁳ of aqueous barium nitrate. Show clearly on Fig. 2.1 how you worked out your answer.
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0620/61 · October/November 2024 · Q2d[2]
The student repeats the experiment using 6.5 cm³ of aqueous barium nitrate. Predict the level of precipitate on the measuring cylinder scale. Explain your answer.
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0620/61 · October/November 2024 · Q2e[2]
Sketch on Fig. 2.1 the graph obtained if all of the experiments are repeated using aqueous barium nitrate of half the concentration used in Experiments 1 to 8.
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What examiners said

Comprehensive responses • Many candidates knew the correct answer to this calculation question. Limited responses • Some candidates confused the ratios in this question and would benefit from more practice on this type of question.
— Examiner report, February/March 2026, 0620/32 Q8(d) (Cambridge)

Most candidates were able to correctly recall the number of particles in one mole. Most candidates gave the syllabus value of 6.02 1023. There is no need for candidates to give this value to 4 significant figures, 6.022 1023.
— Examiner report, February/March 2025, 0620/42 Q1(f) (Cambridge)

This question was done very well by the majority of the candidates and full credit was often seen. Weaker responses calculated the number of moles of Ca(OH)2 used and the Mr of HNO3 only. Candidates should be advised not to use fractions as answers.
— Examiner report, February/March 2024, 0620/42 Q3(g) (Cambridge)

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In the syllabus

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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