AQA A-Level Chemistry: Group 2, the alkaline earth metals (7405) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover section 3.2.2 Group 2, the alkaline earth metals of the AQA AS and A-level Chemistry specification (7404/7405), version 1.2, July 2026, for AS and A-level exams June 2016 onwards, plus the Group 2 part of required practical 4. All of it is AS content, so nothing here is A-level only. The topic is examined on AS Paper 1 and A-level Paper 1, and A-level Paper 3 can test any content.

Learn the ideas first in the Group 2 study guide and the Group 2 revision notes. The course hub is AQA A-Level Chemistry, and the printable checklist lists every specification point. More mole practice is in the amount of substance questions. Use these Aᵣ values: H 1.0, C 12.0, O 16.0, Mg 24.3, S 32.1, Cl 35.5, Ca 40.1, Ti 47.9, Ba 137.3. Use R = 8.31 J K⁻¹ mol⁻¹. A calculator is needed for questions 6, 7, 8, 10 and 11.

Questions

1. Which statement about the Group 2 elements from magnesium to barium is correct?

• A First ionisation energy increases down the group.
• B Magnesium sulfate is the least soluble sulfate.
• C Barium hydroxide is the most soluble hydroxide.
• D Atomic radius decreases down the group.

[1]

2. State the trend in the solubility of the Group 2 sulfates from Mg to Ba, and name the sulfate that the specification describes as insoluble. [2]

3. (a) Write an equation, with state symbols, for the first ionisation energy of magnesium. [1] (b) Explain why strontium has a lower first ionisation energy than magnesium. [3]

4. Explain why calcium has a higher melting point than barium. [3]

5. (a) Write an equation for the reaction of barium with cold water. [1] (b) Write an equation for the reaction of magnesium with steam. [1] (c) State one observation when calcium is added to cold water. [1] (d) Use oxidation states to identify the species reduced in the reaction in (a). [2]

6. Titanium is extracted by the reaction TiCl₄ + 2Mg → Ti + 2MgCl₂.

(a) State the role of magnesium in this reaction. Use oxidation states to explain your answer. [2] (b) A batch uses 3.50 kg of TiCl₄ and 1.00 kg of magnesium. Show that TiCl₄ is the limiting reagent and calculate the maximum mass of titanium formed, in grams, to 3 significant figures. [4]

7. 0.120 g of calcium reacts completely with excess water. Calculate the volume of hydrogen formed, in cm³, at 100 kPa and 298 K. [3]

8. A student makes a saturated solution of calcium hydroxide and filters it. A 25.0 cm³ sample of the filtrate needs 20.0 cm³ of 0.0500 mol dm⁻³ hydrochloric acid for neutralisation.

(a) Write an equation for the reaction. [1] (b) Calculate the concentration of the calcium hydroxide solution in mol dm⁻³. [3] (c) Convert your answer to (b) into g dm⁻³. [1] (d) The student repeats the experiment with a saturated solution of barium hydroxide, using the same volumes and acid. Predict how the titre will change, and explain your answer. [2]

9. A student tests a solution for sulfate ions.

(a) Describe the test and the positive result. Include an ionic equation. [3] (b) Explain why the solution is acidified first. Include an equation. [2] (c) Explain why sulfuric acid must not be used to acidify the solution. [1]

10. A 1.20 g sample of impure Epsom salt, MgSO₄·7H₂O, is dissolved in water. Excess acidified barium chloride is added. The precipitate is filtered, washed and dried; its mass is 1.10 g. Calculate the percentage purity of the sample. Assume the impurities contain no sulfate. [4]

11. A coal-fired power station produces 2.40 tonnes of sulfur dioxide per hour. The SO₂ is removed from the flue gases using calcium oxide.

(a) Explain why calcium oxide can remove sulfur dioxide. [1] (b) Write an equation for the reaction. [1] (c) Calculate the mass of calcium oxide needed per hour, in tonnes, to 3 significant figures. [3] (d) Calculate the mass of calcium sulfite formed per hour, in tonnes. [1] (e) Give one advantage of using calcium oxide instead of calcium carbonate. [1]

12. Three unlabelled solutions contain magnesium chloride, calcium chloride and barium chloride, all at the same concentration. Using only sodium hydroxide solution and dilute sulfuric acid, describe how you would identify each solution. Then explain why barium sulfate, but not barium chloride, can be swallowed for a medical X-ray. [6]

Answers

1. C [1]. [1] Examiner insight: Option B reverses the sulfate trend; check each option’s direction, not just its element.

2. Solubility decreases down the group [1]. Barium sulfate, BaSO₄ [1]. [2] Examiner insight: “Barium” alone does not name the compound; give the sulfate.

3. (a) Mg(g) → Mg⁺(g) + e⁻ [1]. (b) Strontium’s outer electron is in a higher shell (5s against 3s), further from the nucleus [1]. There is more shielding from inner shells [1]. So the outer electron is attracted less strongly and less energy is needed to remove it; this outweighs the larger nuclear charge [1]. [4] Examiner insight: Both state symbols must be (g); writing Mg(s) describes a different process.

4. Both are giant metallic lattices with metallic bonding [1]. Both form 2+ ions, but Ca²⁺ ions are smaller than Ba²⁺ ions, so the delocalised electrons are closer to the nucleus of each ion [1]. The attraction between the ions and the delocalised electrons is stronger in calcium, so more energy is needed to overcome it [1]. [3] Examiner insight: Words such as “intermolecular forces” or “ionic bonds” describe the wrong structure and undermine an otherwise correct answer.

5. (a) Ba + 2H₂O → Ba(OH)₂ + H₂ [1]. (b) Mg + H₂O → MgO + H₂ [1]. (c) Any one: fizzing (effervescence); the calcium dissolves or gets smaller; a white suspension or precipitate forms [1]. (d) Hydrogen in water is reduced [1], from +1 in H₂O to 0 in H₂ [1]. [5] Examiner insight: An observation must be something you see; “hydrogen gas is produced” names a product and is not an observation.

6. (a) Magnesium is the reducing agent [1]: it is oxidised from 0 in Mg to +2 in MgCl₂, while titanium is reduced from +4 to 0 [1]. (b)

Mr(TiCl₄) = 47.9 + (4 × 35.5) = 189.9
n(TiCl₄)  = 3500 ÷ 189.9 = 18.43 mol
n(Mg)     = 1000 ÷ 24.3  = 41.15 mol

n(TiCl₄) = 18.43 mol and n(Mg) = 41.15 mol [1]. Mg needed = 2 × 18.43 = 36.86 mol, which is less than 41.15 mol, so Mg is in excess and TiCl₄ is limiting [1]. n(Ti) = n(TiCl₄) = 18.43 mol [1]. Mass of Ti = 18.43 × 47.9 = 883 g [1]. [6] Examiner insight: “Show that” needs the comparison written out; stating “TiCl₄ is limiting” with no mole values proves nothing.

7. n(Ca) = 0.120 ÷ 40.1 = 2.99 × 10⁻³ mol, and n(H₂) = n(Ca) [1]. V = nRT ÷ p = (2.993 × 10⁻³ × 8.31 × 298) ÷ (100 × 10³) = 7.41 × 10⁻⁵ m³ [1]. V = 74.1 cm³ [1]. [3] Examiner insight: Pressure must be in Pa and the volume comes out in m³; forgetting to convert to cm³ (× 10⁶) loses the final answer.

8. (a) Ca(OH)₂ + 2HCl → CaCl₂ + 2H₂O [1]. (b) n(HCl) = 20.0 × 10⁻³ × 0.0500 = 1.00 × 10⁻³ mol [1]. n(Ca(OH)₂) = 1.00 × 10⁻³ ÷ 2 = 5.00 × 10⁻⁴ mol [1]. Concentration = 5.00 × 10⁻⁴ ÷ 0.0250 = 0.0200 mol dm⁻³ [1]. (c) Mr(Ca(OH)₂) = 74.1; 0.0200 × 74.1 = 1.48 g dm⁻³ [1]. (d) The titre would be larger [1], because barium hydroxide is more soluble than calcium hydroxide, so the saturated solution contains more hydroxide ions to neutralise [1]. [7] Examiner insight: The 2 : 1 ratio in the equation is where most errors start; dividing by 2 before finding the concentration should appear as a separate line of working.

9. (a) Add dilute hydrochloric (or nitric) acid, then barium chloride solution [1]. A white precipitate forms [1]. Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s) [1]. (b) To remove carbonate ions, which would otherwise form a white precipitate of barium carbonate [1]. 2H⁺ + CO₃²⁻ → CO₂ + H₂O [1]. (c) Sulfuric acid contains sulfate ions, so a precipitate would form whether or not the sample contained sulfate [1]. [6] Examiner insight: In (b) the reason must name the interfering ion; “to make the test work” is too vague.

10. Mr(BaSO₄) = 233.4 and Mr(MgSO₄·7H₂O) = 246.4 [1]. n(BaSO₄) = 1.10 ÷ 233.4 = 4.713 × 10⁻³ mol, which equals n(MgSO₄·7H₂O) [1]. Mass of MgSO₄·7H₂O = 4.713 × 10⁻³ × 246.4 = 1.161 g [1]. Purity = 1.161 ÷ 1.20 × 100 = 96.8% [1]. [4] Examiner insight: Leaving the 7H₂O out of the Mr gives a much smaller mass and a wrong percentage; the water of crystallisation is part of the formula.

11. (a) CaO is a base and SO₂ is an acidic oxide, so they react together [1]. (b) CaO + SO₂ → CaSO₃ [1]. (c) Mr(SO₂) = 64.1 and Mr(CaO) = 56.1 [1]. n(SO₂) = 2.40 × 10⁶ ÷ 64.1 = 3.744 × 10⁴ mol [1]. Mass of CaO = 3.744 × 10⁴ × 56.1 = 2.10 × 10⁶ g = 2.10 tonnes [1]. (d) Mr(CaSO₃) = 120.2; 3.744 × 10⁴ × 120.2 = 4.50 tonnes [1]. (e) CaO does not release carbon dioxide (or: all its atoms end up in the useful product) [1]. [7] Examiner insight: Convert tonnes to grams before dividing by Mr, then convert back at the end.

12.

• With NaOH(aq), magnesium chloride gives the most white precipitate, because Mg(OH)₂ is the least soluble hydroxide [1].
• Barium chloride gives the least (or no) precipitate with NaOH, because Ba(OH)₂ is the most soluble [1].
• With dilute H₂SO₄ (fresh samples), barium chloride gives a white precipitate, because BaSO₄ is insoluble; magnesium chloride gives none, because MgSO₄ is soluble [1].
• Calcium chloride gives intermediate results in both tests, so it is the remaining solution [1].
• Barium sulfate is opaque to X-rays, so it shows the outline of the digestive system [1].
• Barium ions are toxic; BaCl₂ is soluble so it would release Ba²⁺ into the body, but BaSO₄ is insoluble so barium ions are not absorbed [1]. [6] Examiner insight: Link each observation to a solubility trend; a bare list of results explains nothing.

Where marks are usually lost

• Explaining a lower ionisation energy down the group without mentioning shielding.
• Writing Mg(OH)₂ as the product of magnesium and steam.
• Swapping the hydroxide and sulfate solubility trends.
• Using sulfuric acid to acidify the sample in the sulfate test.
• Forgetting the 1 : 2 ratio of TiCl₄ to Mg when finding the limiting reagent.
• Leaving pressure in kPa in pV = nRT, or not converting m³ to cm³.

Next steps

• Group 2 revision notes
• Group 2 study guide
• AQA A-Level Chemistry course hub
• Printable AQA A-Level Chemistry checklist
• All free 10-minute diagnostics
• Book a free trial class

Official syllabus

AQA, AS and A-level Chemistry specification (7404/7405), version 1.2, July 2026, for AS and A-level exams June 2016 onwards: section 3.2.2 Group 2, the alkaline earth metals, with required practical 4 (listed in section 3.2.3).