Quick answer: The amount of substance, in mol, links mass, particle number, solution volume and gas volume. This Chemistry 11-12 worksheet on ideal gas equation gives 20 problems from easy to hard: moles of salt, sodium hydroxide solution and unit conversions. The worked answers are on a separate page, and the worksheet is a free printable PDF.
These problems train the core tools of quantitative chemistry: converting between mass, moles, particles, solutions and gases, finding empirical and molecular formulae from masses or combustion data, and using pV = nRT with the correct units.
They suit A Level, IB Chemistry SL and CBSE Class 11-12. The early problems are single steps, and the last five combine several ideas and need careful units.
Level: Chemistry grades 11-12 (A Level · IB · Class 11-12) · Curriculum: A Level 3.1.2
Problem 1 Moles of salt ★★★
Chiamaka in Lagos weighs 117 g of sodium chloride (M = 58.5 g mol⁻¹).1. Calculate the amount of NaCl in mol.
2. Calculate the number of formula units, using 6.02 × 10²³ mol⁻¹.
3. Calculate the mass of 0.250 mol of NaCl.
Problem 2 Sodium hydroxide solution ★★★
A student in Leeds makes 0.250 dm³ of sodium hydroxide solution of concentration 0.400 mol dm⁻³.1. Calculate the amount of NaOH dissolved.
2. Calculate the mass of NaOH needed (M = 40.0 g mol⁻¹).
Problem 3 Unit conversions ★★★
Convert each value to the unit needed for pV = nRT.1. 250 cm³ to m³
2. 101 kPa to Pa
3. 27 °C to K
4. 2.40 dm³ to m³
Problem 4 Formula of an iron oxide ★★★
A sample contains 5.60 g of iron and 2.40 g of oxygen (Ar: Fe 56.0, O 16.0).1. Calculate the amount of each element.
2. Find the simplest whole-number ratio.
3. Write the empirical formula.
Problem 5 Vitamin C in a tablet ★★★
Vitamin C is C₆H₈O₆ (Ar: C 12.0, H 1.0, O 16.0). A tablet contains 500 mg.1. Calculate the molar mass.
2. Calculate the amount in mol in one tablet.
Problem 6 Why is atom economy 100 %? ★★★
Ethene reacts with steam: C₂H₄ + H₂O → C₂H₅OH.1. State the atom economy for making ethanol this way.
2. Explain why it takes this value.
Problem 7 Formula of sodium sulfate ★★★
A compound contains 32.4 % sodium, 22.6 % sulfur and 45.0 % oxygen by mass (Ar: Na 23.0, S 32.1, O 16.0).1. Calculate the amount of each element in 100 g.
2. Deduce the empirical formula.
Problem 8 Carbon dioxide at room conditions ★★★
Take R = 8.31 J K⁻¹ mol⁻¹.1. Calculate the volume in dm³ of 0.0800 mol of carbon dioxide at 25 °C and 100 kPa.
Problem 9 Gas in a cylinder ★★★
A cylinder of volume 2.40 dm³ holds oxygen at 1.50 × 10⁵ Pa and 20 °C.1. Calculate the amount of oxygen in mol.
2. Calculate its mass (M = 32.0 g mol⁻¹).
Problem 10 Molar mass of a volatile liquid ★★★
A student injects 0.150 g of a volatile liquid into the heated gas syringe. It becomes 62.0 cm³ of vapour at 100 °C and 101 kPa.2. Calculate the amount of vapour.
3. Calculate the molar mass of the liquid.
Problem 11 Phosphorus oxide ★★★
An oxide of phosphorus has empirical formula P₂O₅ and molar mass 284 g mol⁻¹ (Ar: P 31.0, O 16.0).1. Calculate the mass of the empirical formula unit.
2. Deduce the molecular formula.
Problem 12 Burning an organic liquid ★★★
A compound of carbon, hydrogen and oxygen (0.740 g, M = 74.0 g mol⁻¹) burns completely. The absorbers gain 0.900 g of water and 1.76 g of carbon dioxide.2. Calculate the mass of oxygen in the sample by difference.
3. Deduce the empirical and molecular formulae.
Problem 13 Atom economy in iron making ★★★
Iron is made in the reaction Fe₂O₃ + 3CO → 2Fe + 3CO₂ (Ar of Fe = 55.8; Mr of CO₂ = 44.0).1. Calculate the total mass of products per mole of equation.
2. Calculate the atom economy for iron.
Problem 14 Percentage yield of ethyl ethanoate ★★★
Emma in Leeds heats 4.60 g of ethanol (M = 46.0) with excess ethanoic acid and obtains 3.10 g of ethyl ethanoate (M = 88.0). The equation is 1 : 1.1. Calculate the maximum mass of ester.
2. Calculate the percentage yield.
Problem 15 Hydrated copper sulfate ★★★
Heating 2.50 g of CuSO₄·xH₂O leaves 1.60 g of anhydrous CuSO₄ (M = 159.6; H₂O = 18.0).1. Calculate the mass and the amount of water lost.
2. Calculate the amount of CuSO₄.
3. Deduce the value of x.
Problem 16 Reading a pressure graph ★★★
The graph is for a fixed amount of gas at 300 K, with V in dm³.2. Calculate n.
3. State what happens to the gradient if the temperature rises to 350 K.
Problem 17 Identifying a gas from density ★★★
A gas has density 1.94 g dm⁻³ at 25 °C and 100 kPa.1. Show that M = ρRT / p, where ρ is the density.
2. Calculate the molar mass.
3. Suggest the gas from O₂, O₃ and N₂O (Ar: N 14.0, O 16.0).
Problem 18 Gas from baking soda ★★★
Sodium hydrogencarbonate decomposes on heating: 2NaHCO₃(s) → Na₂CO₃(s) + H₂O(g) + CO₂(g). A baker heats 4.20 g (M = 84.0) to 200 °C at 100 kPa.1. Calculate the amount of NaHCO₃.
2. Calculate the total amount of gas formed, counting steam and CO₂.
3. Calculate the volume of gas in dm³.
Problem 19 Two routes to hydrogen ★★★
Route A: CH₄ + H₂O → CO + 3H₂. Route B: CH₄ + 2H₂O → CO₂ + 4H₂. (Mr: CO 28.0, CO₂ 44.0, H₂ 2.0.)1. Calculate the atom economy for hydrogen in each route.
2. Compare them and give one reason atom economy alone cannot decide the better route.
Problem 20 Hydrocarbon from gas data ★★★
A hydrocarbon contains 85.7 % carbon by mass. A 0.280 g sample forms 155 cm³ of vapour at 100 °C and 100 kPa.1. Calculate the amount of vapour and the molar mass.
2. Find the empirical formula.
3. Deduce the molecular formula.
