Atoms, molecules and stoichiometry — AS & A Level Chemistry (9701) questions by topic
Formula-writing and gas-volume stoichiometry anchor this small topic: identifying correctly paired ionic formulae, calculating gas volume from a copper carbonate and hydrochloric acid reaction, and comparing which 1.0 g carbonate sample releases the most CO2.
Calculate, identify, deduce and predict are the command words across 31 questions from 2023 to 2025 papers, worth 1 to 9 marks, where balancing an equation correctly is the gateway to every subsequent mole calculation. With only one recorded common mistake against no logged strong-answer comments, instant marking is most valuable here for confirming a balanced equation such as Al4C3 + NaOH + H2O is complete before the mole ratios built on it are trusted.
What examiners look for
- Examiners note the most commonly chosen incorrect answer required constructing the balanced equation Al4C3 + 4NaOH + 4H2O -> 4NaAlO2 + 3CH4, balancing aluminium and sodium first, then oxygen using water, before carbon and hydrogen give methane.
- A recurring point is that skipping the full balancing sequence for aluminium, sodium, oxygen, then carbon and hydrogen was the source of the commonest wrong choice.
May–June 2025, Paper 11
ICl3 reacts with water in a redox reaction. vICl3 + wH2O → xHCl + yHI + zHIO3 + zHClO3 What are the numbers v, x and z in the correctly balanced equation? A v=2, x=8, z=1 B v=2,…
Answer this question and get it marked →Barium dithionate, BaS2O6·2H2O, is soluble in water. S2O6^2-(aq) ions slowly decompose in acidic solution: S2O6^2-(aq) → SO2(g) + SO4^2-(aq) 3.513 g of BaS2O6·2H2O is dissolved in…
Answer this question and get it marked →May–June 2025, Paper 12
An experiment is carried out to determine the value of x in hydrated lithium hydroxide, LiOH·xH2O. A sample of the solid is heated in a crucible over a Bunsen flame. Complete…
Answer this question and get it marked →May–June 2025, Paper 13
Hydrogen peroxide, H2O2, decomposes into water and oxygen when a suitable catalyst is added. 20.0 cm^3 of aqueous hydrogen peroxide decomposes to produce 600 cm^3 of oxygen at…
Answer this question and get it marked →A washing powder contains sodium hydrogencarbonate, NaHCO3, as one of the ingredients. In a titration, a solution containing 1.00 g of this washing powder requires 7.15 cm^3 of…
Answer this question and get it marked →May–June 2025, Paper 14
A 69.0 g sample of nitrogen dioxide is placed in a reaction vessel. The initial pressure of the nitrogen dioxide is P. An effective catalyst is then added and the nitrogen dioxide…
Answer this question and get it marked →The juice of one lemon reacts completely with 120 cm^3 of 0.50 mol dm^-3 sodium carbonate solution. The formula of citric acid is HOOCCH2C(OH)(COOH)CH2COOH. No sodium carbonate is…
Answer this question and get it marked →May–June 2025, Paper 21
Deduce the empirical formula of vitamin C (molecular formula C6H8O6).
Answer this question and get it marked →May–June 2025, Paper 22
Deduce the empirical formula of vitamin C (molecular formula C6H8O6).
Answer this question and get it marked →May–June 2024, Paper 11
Sample X is added to water and made up to a total volume of 200 cm^3. This gives a solution of 0.100 mol dm^-3 HCl. What is X? A 10 cm^3 of 1.00 mol dm^-3 HCl B 30 cm^3 of 0.90…
Answer this question and get it marked →A mixture of 10 cm^3 of methane and 10 cm^3 of ethane was sparked with an excess of oxygen. After cooling, the residual gas was passed through aqueous potassium hydroxide. All gas…
Answer this question and get it marked →May–June 2024, Paper 12
Which pair of formulae is correct? A Ag2CO3 and (NH4)3NO3 B K2HCO3 and Zn3(PO4)2 C AgHCO3 and K3PO4 D ZnCO3 and (NH4)2PO4
Answer this question and get it marked →How many molecules are present in 62 g of solid white phosphorus, P4? (L is the Avogadro constant.) A L B 2L C L/2 D L/4
Answer this question and get it marked →May–June 2024, Paper 13
X is an impure sample of a Group 2 metal carbonate, MCO3. X contains 57% by mass of MCO3. The impurities in X do not react with hydrochloric acid. 7.4 g of X is reacted with an…
Answer this question and get it marked →Which of these samples of gas contains the same number of atoms as 1 g of hydrogen gas? A 22 g of carbon dioxide (Mr: CO2, 44) B 8 g of methane (Mr: CH4, 16) C 20 g of neon (Mr:…
Answer this question and get it marked →October–November 2024, Paper 11
Glauber's salt consists of crystals of hydrated sodium sulfate, Na₂SO₄•xH₂O, which can be used for the manufacture of detergents. When a sample of Glauber's salt was heated, 1.91…
Answer this question and get it marked →What contains the greatest number of the named particles? A 6.0 dm³ of argon atoms at room conditions B 6.0 g of carbon dioxide molecules C 6.0 g of magnesium atoms D 6.0 g of…
Answer this question and get it marked →7.5 g of nitrogen monoxide reacts with 7.0 g of carbon monoxide on the surface of the catalytic converter in the exhaust system of a car. What is the total volume of the product…
Answer this question and get it marked →October–November 2024, Paper 12
A 0.216 g sample of aluminium carbide reacts with an excess of water to produce methane gas. This is the only carbon-containing product formed in the reaction. This methane gas…
Answer this question and get it marked →October–November 2024, Paper 13
Glauber's salt consists of crystals of hydrated sodium sulfate, Na₂SO₄•xH₂O, which can be used for the manufacture of detergents. When a sample of Glauber's salt was heated, 1.91…
Answer this question and get it marked →What contains the greatest number of the named particles? A 6.0 dm³ of argon atoms at room conditions B 6.0 g of carbon dioxide molecules C 6.0 g of magnesium atoms D 6.0 g of…
Answer this question and get it marked →7.5 g of nitrogen monoxide reacts with 7.0 g of carbon monoxide on the surface of the catalytic converter in the exhaust system of a car. What is the total volume of the product…
Answer this question and get it marked →February–March 2023, Paper 12
Molten aluminium chloride has a simple molecular structure. Each molecule consists of two aluminium atoms and six chlorine atoms. Which statement is correct? A All the chlorine…
Answer this question and get it marked →May–June 2023, Paper 11
Which statement is correct? A The relative atomic mass of a ³⁵Cl atom is 35.5. B The relative formula mass of CaCO3 is 100.1. C The relative isotopic mass of a ²⁴Mg atom is 24.3.…
Answer this question and get it marked →May–June 2023, Paper 12
If 1 mol of hexane combusts in an excess of oxygen, how many moles of products are formed? A 11 B 12 C 13 D 14
Answer this question and get it marked →Separate samples, each of mass 1.0 g, of the compounds listed are treated with an excess of dilute acid. Which compound releases the largest amount of CO2? A 1.0 g CaCO3 B 1.0 g…
Answer this question and get it marked →May–June 2023, Paper 13
A piece of rock has a mass of 2.00 g. It contains calcium carbonate, but no other basic substances. It neutralises exactly 36.0 cm3 of 0.500 mol dm^-3 hydrochloric acid. What is…
Answer this question and get it marked →October–November 2023, Paper 11
Aluminium carbide, Al4C3, reacts readily with aqueous sodium hydroxide. The two products of the reaction are NaAlO2 and a hydrocarbon. Water molecules are also involved as…
Answer this question and get it marked →If ammonium cyanate is heated in the absence of air, the only product of the reaction is urea, CO(NH2)2; no other products are formed. What is the formula of the cyanate ion…
Answer this question and get it marked →October–November 2023, Paper 12
A 3.7 g sample of copper(II) carbonate is added to 25 cm3 of 2.0 mol dm-3 hydrochloric acid. Which volume of gas is produced at room conditions? A: 0.60 dm3. B: 0.72 dm3. C: 1.20…
Answer this question and get it marked →October–November 2023, Paper 13
A sample of 35.6 g of hydrated sodium carbonate contains 25.84% sodium ions by mass. When this sample is heated, anhydrous sodium carbonate and water are formed. Which mass of…
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