2022 May/June · Paper 13 · Q211 markThermal decomposition of nitrates & carbonates
2022 May/June · Paper 21 · Q1 (b(i), b(ii), c, f(i))4 marksGroup 2 hydroxide & sulfate solubility · Group 2 reactions with water & oxygen · Thermal decomposition of nitrates & carbonates
2022 May/June · Paper 22 · Q2 (c(i), c(ii), c(iii), c(iv))6 marksGroup 2 reactions with water & oxygen
2022 May/June · Paper 41 · Q1 (a, b)4 marksGroup 2 hydroxide & sulfate solubility · Group 2 solubility & thermal stability trends (A Level)
2022 May/June · Paper 42 · Q1 (a)3 marksGroup 2 solubility & thermal stability trends (A Level)
2022 May/June · Paper 42 · Q4 (b(i), b(ii))3 marksGroup 2 solubility & thermal stability trends (A Level)
2022 May/June · Paper 43 · Q1 (a, b)4 marksGroup 2 hydroxide & sulfate solubility · Group 2 solubility & thermal stability trends (A Level)
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Practice questions
Original questions written by HomiLabs in the style of the exam, with answers and mark schemes. They are not
Cambridge past paper questions and have not been reviewed by Cambridge. Try each one before opening the answer.
Q1Thermal decomposition of nitrates & carbonates · Core · Paper 2 style · 5 marks
(a)Write an equation for the thermal decomposition of calcium nitrate.[2]
(b)State two observations you would make when calcium nitrate is heated strongly in a test-tube.[2]
(c)Write an equation for the thermal decomposition of strontium carbonate.[1]
Show answer
(a) 2Ca(NO₃)₂ → 2CaO + 4NO₂ + O₂
B1 correct products. B1 balanced.
(b) brown gas given off; a glowing splint relights (oxygen) / white solid remains
1 mark each for any two of: brown fumes (NO₂); glowing splint relights; white solid residue; crystals may melt/crackle.
(c) SrCO₃ → SrO + CO₂
B1.
Q2Thermal decomposition of nitrates & carbonates · Core · Paper 1 style · 1 mark
(a)0.0100 mol of magnesium nitrate is heated until decomposition is complete. What is the total volume of gas produced, measured at room conditions? (Molar gas volume = 24.0 dm³ mol⁻¹ at room conditions)[1]
Show answer
(a) C 600 cm³
2Mg(NO₃)₂ → 2MgO + 4NO₂ + O₂: 0.0100 mol gives 0.0200 mol NO₂ + 0.00500 mol O₂ = 0.0250 mol = 600 cm³. B counts only the NO₂; A counts only the O₂.
Q3Thermal decomposition of nitrates & carbonates · Core · Paper 2 style · 3 marks
(a)Magnesium carbonate is used as a drying agent for climbers' hands. Write an equation for its thermal decomposition.[1]
(b)Calculate the mass of solid remaining when 5.00 g of magnesium carbonate is heated to constant mass. Give your answer to 3 significant figures. (Mr: MgCO₃ 84.3, MgO 40.3)[2]
Show answer
(a) MgCO₃ → MgO + CO₂
B1.
(b) 2.39 g
M1 n = 5.00 ÷ 84.3 = 0.0593 mol. A1 × 40.3 = 2.39 g.
Q4Thermal decomposition of nitrates & carbonates · Standard · Paper 3 style · 5 marks
(a)A student heats a sample of a Group 2 carbonate, MCO₃, in a crucible to constant mass.mass of empty crucible = 18.452 gmass of crucible + MCO₃ = 21.047 gmass after first heating = 20.414 gmass after second heating = 20.274 gmass after third heating = 20.273 gExplain why the student heated the crucible three times.[1]
(b)Calculate the mass of carbon dioxide given off and the amount, in mol, of CO₂.[2]
(c)Calculate the Mr of MCO₃ and hence identify M.[2]
Show answer
(a) To make sure decomposition was complete (heating to constant mass)
B1 the last two masses agree (within 0.001 g), showing all the carbonate has decomposed.
Q5Thermal decomposition of nitrates & carbonates · Standard · Paper 2 style · 4 marks
(a)Barium nitrate is used in green fireworks. Calculate the total volume of gas, in cm³ at room conditions, released when 2.61 g of barium nitrate (Mr 261.3) is fully decomposed by heat. Give your answer to 3 significant figures.[3]
(b)Barium nitrate must be heated more strongly than magnesium nitrate to decompose it. State what this tells you about the thermal stability of the Group 2 nitrates.[1]
Q6Thermal decomposition of nitrates & carbonates · Standard · Paper 1 style · 1 mark
(a)Equal amounts of four Group 2 nitrates are heated in the same way. Which nitrate gives a brown gas at the lowest temperature?[1]
Show answer
(a) C magnesium nitrate
Thermal stability of Group 2 nitrates increases down the group, so magnesium nitrate decomposes most easily. A (barium nitrate) is the most stable and is chosen by students who reverse the trend.
Q7Thermal decomposition of nitrates & carbonates · Standard · Paper 5 style · 6 marks
(a)Plan an experiment to compare the thermal stabilities of magnesium carbonate, calcium carbonate and barium carbonate using limewater. State the independent variable, the dependent variable and two variables that must be controlled.[4]
(b)State one safety precaution specific to this experiment and explain it.[1]
(c)Suggest why using equal masses rather than equal amounts in moles of each carbonate would make the comparison less fair.[1]
Show answer
(a) IV: the carbonate (identity of Group 2 metal). DV: time for limewater to turn milky. Controls: same amount (moles) of carbonate; same burner flame / heat; same volume and concentration of limewater; same tube size
B1 IV. B1 DV (time for cloudiness). B1 B1 any two controls; same mass is acceptable only if moles discussed as limitation.
(b) Remove the delivery tube from the limewater before stopping heating, to prevent suck-back of cold liquid into the hot tube (which could crack it)
B1 precaution with reason. Accept eye protection with reason, barium compounds are toxic – avoid ingestion/wash hands.
(c) The carbonates have different Mr, so equal masses contain different numbers of moles and give different amounts of CO₂
B1.
Q8Thermal decomposition of nitrates & carbonates · Challenge · Paper 2 style · 6 marks
(a)A 4.00 g sample of dolomitic limestone from the Salt Range contains only calcium carbonate and magnesium carbonate. After heating to constant mass, 2.118 g of solid remains. Write equations for the two decompositions.[2]
(b)Calculate the percentage by mass of calcium carbonate in the sample. Give your answer to 3 significant figures. (Mr: CaCO₃ 100.1, CaO 56.1, MgCO₃ 84.3, MgO 40.3)[4]
Show answer
(a) CaCO₃ → CaO + CO₂; MgCO₃ → MgO + CO₂
B1 each.
(b) 62.4 %
M1 let mass CaCO₃ = x g: residue = x(56.1/100.1) + (4.00 − x)(40.3/84.3). M1 2.118 = 0.5604x + 0.4781(4.00 − x). M1 x = 2.50 g. A1 62.4 %.
Q9Thermal decomposition of nitrates & carbonates · Challenge · Paper 2 style · 5 marks
(a)1.48 g of magnesium nitrate (Mr 148.3) is heated until there is no further change. Calculate the mass of the solid residue. Give your answer to 3 significant figures.[2]
(b)The gases are passed through aqueous sodium hydroxide, which absorbs all the nitrogen dioxide. Calculate the volume of gas, in cm³ at room conditions, that leaves the sodium hydroxide.[2]
(c)Suggest why the residue from heating magnesium nitrate is used to line some furnaces.[1]
Show answer
(a) 0.402 g
M1 n = 0.00998 mol; n(MgO) = n(nitrate). A1 × 40.3 = 0.402 g.
(c) MgO has a very high melting point (giant ionic lattice with strong attraction between small, doubly charged ions)
B1 high melting point / refractory.
Q10Thermal decomposition of nitrates & carbonates · Challenge · Paper 2 style · 4 marks
(a)3.00 g of a Group 2 nitrate, M(NO₃)₂, is heated until decomposition is complete, leaving 1.469 g of the oxide MO. Show that the Ar of M is given by the equation 1.469(Ar + 124) = 3.00(Ar + 16).[2]
(b)Solve the equation to find Ar and identify M.[2]
B1 Mr of M(NO₃)₂ = Ar + 124.0 and Mr of MO = Ar + 16.0. B1 equal amounts in mol leads to the equation.
(b) Ar = 87.6; strontium
M1 3.00 × 16 − 1.469 × 124 = (1.469 − 3.00)Ar so Ar = 87.6. A1 Sr.
Q11Group 2 solubility & thermal stability trends (A Level) · Core · Paper 4 style · 4 marks
(a)State the trend in thermal stability of the Group 2 carbonates down the group.[1]
(b)Explain this trend.[3]
Show answer
(a) increases (decomposition temperature increases)
B1.
(b) Cation radius increases down the group, so charge density decreases; the cation polarises the carbonate ion (distorts its electron cloud) less; the C–O bonds are weakened less, so more energy is needed to decompose
B1 ionic radius of M²⁺ increases / charge density decreases. B1 less polarisation of the CO₃²⁻ anion. B1 C–O bond less weakened, so higher temperature needed. Do not credit 'polarisation of the cation'.
Q12Group 2 solubility & thermal stability trends (A Level) · Core · Paper 4 style · 4 marks
(a)Write an expression for the enthalpy change of solution of MgSO₄ in terms of its lattice energy and the enthalpy changes of hydration of its ions.[1]
(b)Explain why the solubility of the Group 2 sulfates decreases down the group.[3]
B1 (lattice energy defined as exothermic formation of the lattice from gaseous ions).
(b) Lattice energy becomes only slightly less exothermic (dominated by the large sulfate ion); hydration enthalpy of the cation becomes much less exothermic as the cation gets larger; so ΔHsol becomes more endothermic and solubility decreases
B1 lattice energy decreases only slightly because SO₄²⁻ is large. B1 hydration enthalpy decreases considerably as cation radius increases. B1 ΔHsol less exothermic / more endothermic, so less soluble.
Q13Group 2 solubility & thermal stability trends (A Level) · Core · Paper 4 style · 4 marks
(a)Explain why barium hydroxide is more soluble in water than magnesium hydroxide.[3]
(b)Suggest why the trend for hydroxides is the opposite of the trend for sulfates.[1]
Show answer
(a) OH⁻ is small, so lattice energy depends strongly on cation size and decreases a lot down the group; hydration enthalpy of the cation decreases less; ΔHsol becomes more exothermic (less endothermic) for Ba(OH)₂
B1 lattice energy falls more than hydration enthalpy down the group. B1 reason: small anion so inter-ionic distance changes greatly with cation radius. B1 ΔHsol more negative for Ba(OH)₂, so more soluble.
(b) The anions differ in size: with the small OH⁻ the lattice energy change dominates; with the large SO₄²⁻ the hydration enthalpy change dominates
B1.
Q14Group 2 solubility & thermal stability trends (A Level) · Standard · Paper 4 style · 6 marks
(a)Use these data (kJ mol⁻¹) to calculate the enthalpy change of solution of MgSO₄ and of BaSO₄.ΔHhyd: Mg²⁺ −1920; Ba²⁺ −1360; SO₄²⁻ −1160lattice energy: MgSO₄ −2989; BaSO₄ −2546[2]
(b)Use your answers to explain why barium sulfate is used in 'barium meals' for X-ray imaging of the gut, while magnesium sulfate is used as a bath salt.[2]
(c)Calculate the difference between the lattice energies of the two sulfates and the difference between the hydration enthalpies of Mg²⁺ and Ba²⁺. Use these to explain the trend.[2]
(b) ΔHsol of BaSO₄ is endothermic (+26), which together with the much larger hydration-enthalpy loss for Ba²⁺ is consistent with BaSO₄ being very insoluble – so toxic Ba²⁺ ions are not absorbed from the gut; ΔHsol of MgSO₄ is exothermic (−91) and MgSO₄ is soluble, so it dissolves in bath water
B1 BaSO₄: endothermic ΔHsol linked to very low solubility, so barium ions are not absorbed (safe). B1 MgSO₄: exothermic ΔHsol linked to high solubility.
(c) lattice energies differ by 443 kJ mol⁻¹; hydration enthalpies by 560 kJ mol⁻¹
B1 both differences. B1 hydration enthalpy falls by more (560) than lattice energy (443), so ΔHsol becomes more endothermic down the group.
Q15Group 2 solubility & thermal stability trends (A Level) · Standard · Paper 4 style · 4 marks
(a)Use these data (kJ mol⁻¹) to calculate the enthalpy change of hydration of Sr²⁺.lattice energy of SrCl₂ = −2156enthalpy change of solution of SrCl₂ = −52enthalpy change of hydration of Cl⁻ = −364[2]
(b)Predict, with a reason, whether the enthalpy change of hydration of Ca²⁺ is more or less exothermic than your answer.[2]
(b) More exothermic; Ca²⁺ is smaller with a higher charge density, so it attracts water molecules more strongly
B1 more exothermic. B1 smaller ion / higher charge density – stronger ion–dipole attraction.
Q16Group 2 solubility & thermal stability trends (A Level) · Standard · Paper 4 style · 5 marks
(a)The ionic radii are Mg²⁺ 0.072 nm and Ba²⁺ 0.135 nm. Use these data to explain why barium carbonate must be heated to a much higher temperature than magnesium carbonate before it decomposes.[3]
(b)Magnesium oxide has a higher lattice energy than barium oxide. Explain how this also favours the decomposition of MgCO₃.[2]
Show answer
(a) Mg²⁺ is smaller with the same charge, so higher charge density; it polarises the carbonate ion more, weakening a C–O bond; MgCO₃ decomposes at a lower temperature, BaCO₃ needs a higher temperature
B1 Mg²⁺ higher charge density. B1 greater polarisation / distortion of CO₃²⁻ electron cloud. B1 C–O bond weakened more, so MgCO₃ less stable.
(b) The smaller Mg²⁺ forms a much more exothermic lattice with the small O²⁻ ion, so the products of decomposition are relatively more stable; ΔH of decomposition is less endothermic
B1 MgO lattice energy much more exothermic than BaO. B1 makes decomposition less endothermic for MgCO₃.
Q17Group 2 solubility & thermal stability trends (A Level) · Standard · Paper 4 style · 4 marks
(a)Beryllium carbonate is very unstable and decomposes near room temperature. Suggest an explanation in terms of the Be²⁺ ion.[2]
(b)Predict how the thermal stability of radium carbonate compares with that of barium carbonate. Explain.[2]
Show answer
(a) Be²⁺ is extremely small with very high charge density; it strongly polarises the carbonate ion
B1 very small ion / very high charge density. B1 strong polarisation of CO₃²⁻ weakens C–O bonds.
(b) More stable; Ra²⁺ is larger, lower charge density, polarises carbonate less
B1 more stable / higher decomposition temperature. B1 reason.
Q18Group 2 solubility & thermal stability trends (A Level) · Challenge · Paper 4 style · 7 marks
(a)Use these standard enthalpy changes of formation (kJ mol⁻¹) to calculate ΔH for the decomposition of calcium carbonate: CaCO₃ −1207; CaO −635; CO₂ −394.[2]
(b)ΔS for the decomposition is +161 J K⁻¹ mol⁻¹. Calculate the minimum temperature at which the decomposition becomes feasible. Give your answer to 3 significant figures.[2]
(c)Values of ΔH for decomposition are: MgCO₃ +117, CaCO₃ +178, SrCO₃ +234, BaCO₃ +267 kJ mol⁻¹. The values of ΔS are similar. Explain how these data are consistent with the trend in thermal stability, and give the chemical reason for the trend.[3]
M1 ΔG = 0 when T = ΔH/ΔS = 178 × 1000 ÷ 161. A1 1110 K.
(c) ΔH becomes more endothermic down the group, so T = ΔH/ΔS increases – stability increases; larger cations with lower charge density polarise the carbonate ion less
B1 increasing ΔH so higher decomposition temperature. B1 cation radius increases / charge density decreases. B1 less polarisation of anion.
Q19Group 2 solubility & thermal stability trends (A Level) · Challenge · Paper 4 style · 6 marks
(a)Lattice energies (kJ mol⁻¹): MgO −3791; BaO −3054; MgSO₄ −2989; BaSO₄ −2546. Calculate the change in lattice energy from Mg to Ba for the oxides and for the sulfates.[2]
(b)Explain why the lattice energy changes much more for the oxides than for the sulfates.[2]
(c)The radius of Ca²⁺ (0.100 nm) lies between those of Mg²⁺ (0.072 nm) and Ba²⁺ (0.135 nm). Predict, with a reason, how the lattice energy of CaSO₄ compares with those of MgSO₄ and BaSO₄, and state whether CaSO₄ is more or less soluble in water than MgSO₄.[2]
Show answer
(a) oxides: 737 kJ mol⁻¹ less exothermic; sulfates: 443 kJ mol⁻¹ less exothermic
B1 737. B1 443.
(b) Lattice energy depends on the sum of ionic radii; O²⁻ is small so changing the cation from Mg²⁺ to Ba²⁺ makes a large fractional change in the inter-ionic distance; SO₄²⁻ is large so the fractional change is small
B1 lattice energy ∝ 1/(r⁺ + r⁻). B1 large anion means cation size has a smaller effect.
(c) Lattice energy of CaSO₄ lies between −2989 and −2546 kJ mol⁻¹ (less exothermic than MgSO₄, more exothermic than BaSO₄) because Ca²⁺ is intermediate in size; CaSO₄ is less soluble than MgSO₄
B1 between the two values, with reason: larger cation → greater inter-ionic distance → weaker attraction. B1 less soluble than MgSO₄ (sulfate solubility decreases down the group).
Q20Group 2 solubility & thermal stability trends (A Level) · Challenge · Paper 4 style · 6 marks
(a)Lithium nitrate decomposes in the same way as Group 2 nitrates, but sodium nitrate decomposes to sodium nitrite and oxygen. Write equations for the decomposition of lithium nitrate and of sodium nitrate.[2]
(b)Li⁺ has an ionic radius of 0.076 nm, similar to Mg²⁺ (0.072 nm). Na⁺ has a radius of 0.102 nm. Use the idea of charge density to explain why LiNO₃ behaves like Mg(NO₃)₂ and why NaNO₃ is more thermally stable.[3]
(c)Predict whether magnesium nitrate or calcium nitrate would release nitrogen dioxide at a lower temperature, giving a reason.[1]
(b) Li⁺ is small, so its charge density is high enough to polarise the nitrate ion strongly, like Mg²⁺; Na⁺ is larger with the same +1 charge, so lower charge density; nitrate ion is polarised less, so NaNO₃ does not decompose to the oxide
B1 Li⁺ small, high charge density (comparable effect to Mg²⁺). B1 polarises NO₃⁻, weakening N–O bonds. B1 Na⁺ lower charge density – less polarisation – more stable.
(c) magnesium nitrate; Mg²⁺ is smaller with higher charge density so it polarises the nitrate ion more
B1 both.
Q21Group 2 hydroxide & sulfate solubility · Core · Paper 1 style · 1 mark
(a)[1]
Show answer
(a) A dilute sulfuric acid
BaSO₄ is insoluble but MgSO₄ is soluble. C is the main distractor: aqueous NaOH gives a white precipitate of Mg(OH)₂ with Mg²⁺, not with Ba²⁺ (barium hydroxide is fairly soluble).
Q22Group 2 hydroxide & sulfate solubility · Core · Paper 2 style · 4 marks
(a)State the trends in solubility down Group 2 of (i) the hydroxides and (ii) the sulfates.[2]
(b)Magnesium hydroxide is used in some antacid tablets sold in Pakistani pharmacies. Write an equation for its reaction with stomach acid (hydrochloric acid).[1]
(c)Suggest why magnesium hydroxide is preferred to calcium hydroxide or barium hydroxide as an antacid.[1]
Show answer
(a) (i) hydroxides become more soluble; (ii) sulfates become less soluble
B1 each.
(b) Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O
B1.
(c) It is only sparingly soluble, so the solution is only weakly alkaline (and Mg²⁺ is not toxic, unlike Ba²⁺)
B1 low solubility gives mild alkalinity / Ba compounds toxic.
Q23Group 2 hydroxide & sulfate solubility · Standard · Paper 2 style · 6 marks
(a)Aqueous sodium hydroxide is added drop by drop to separate solutions of magnesium chloride and barium chloride of the same concentration. Describe and explain what is seen in each case.[3]
(b)Write an ionic equation, with state symbols, for the formation of the precipitate.[2]
(c)Dilute sulfuric acid is then added to a fresh sample of each solution. Describe what is seen.[1]
Show answer
(a) MgCl₂: white precipitate; BaCl₂: no precipitate (or only a very faint one); Mg(OH)₂ is sparingly soluble, Ba(OH)₂ is much more soluble
B1 white ppt with Mg²⁺. B1 no (or faint) ppt with Ba²⁺. B1 solubility of hydroxides increases down the group.
(b) Mg²⁺(aq) + 2OH⁻(aq) → Mg(OH)₂(s)
B1 equation. B1 state symbols.
(c) white precipitate (BaSO₄) with barium chloride; no change with magnesium chloride
B1.
Q24Group 2 hydroxide & sulfate solubility · Challenge · Paper 3 style · 6 marks
(a)Three solutions, P, Q and R, are calcium nitrate, magnesium nitrate and barium nitrate, but not in that order. Results:P: aqueous NaOH – white precipitate, insoluble in excess; aqueous NH₃ – white precipitate; dilute H₂SO₄ – no changeQ: aqueous NaOH – no precipitate; aqueous NH₃ – no precipitate; dilute H₂SO₄ – dense white precipitateR: aqueous NaOH – white precipitate, insoluble in excess; aqueous NH₃ – no precipitate; dilute H₂SO₄ – slight white precipitateIdentify P, Q and R.[3]
(b)Explain why R gives only a slight precipitate with dilute sulfuric acid while Q gives a dense one.[2]
(c)Explain why aqueous ammonia gives a precipitate with P but not with R.[1]
Show answer
(a) P magnesium nitrate; Q barium nitrate; R calcium nitrate
B1 each.
(b) CaSO₄ is slightly soluble; BaSO₄ is much less soluble (sulfate solubility decreases down the group)
(c) Aqueous ammonia gives only a low concentration of OH⁻; this is enough to exceed the solubility of Mg(OH)₂ but not of the more soluble Ca(OH)₂
B1.
Q25Group 2 reactions with water & oxygen · Core · Paper 2 style · 5 marks
(a)Write an equation for the reaction of calcium with cold water and describe two observations.[3]
(b)Magnesium reacts only very slowly with cold water. Write an equation for this reaction.[1]
(c)Write an equation for the reaction of strontium with oxygen to form its oxide.[1]
Show answer
(a) Ca + 2H₂O → Ca(OH)₂ + H₂; fizzing/bubbles; calcium sinks/disappears; cloudy white suspension forms
B1 equation. B1 B1 any two observations: effervescence, metal disappears, milky solution / white solid, warmth.
(b) Mg + 2H₂O → Mg(OH)₂ + H₂
B1 (hydroxide, not oxide, with cold water).
(c) 2Sr + O₂ → 2SrO
B1.
Q26Group 2 reactions with water & oxygen · Standard · Paper 1 style · 1 mark
(a)Which equation correctly represents the reaction of magnesium with steam?[1]
Show answer
(a) B Mg + H₂O → MgO + H₂
With steam, magnesium forms the oxide and hydrogen. A is the slow reaction with cold water, which forms the hydroxide.
Q27Group 2 reactions with water & oxygen · Challenge · Paper 2 style · 5 marks
(a)0.100 g of calcium reacts completely with water and the solution is made up to 250 cm³. Calculate the volume of hydrogen produced, in cm³ at room conditions. Give your answer to 3 significant figures.[2]
(b)Calculate the concentration of hydroxide ions in the solution.[1]
(c)Calculate the volume of 0.0200 mol dm⁻³ hydrochloric acid needed to neutralise 25.0 cm³ of the solution.[2]
Q28Group 2 reactivity & carbonate stability · Core · Paper 1 style · 1 mark
(a)Why does the reactivity of the Group 2 elements with water increase down the group?[1]
Show answer
(a) A The first and second ionisation energies decrease.
Less energy is needed to remove the two outer electrons, so M²⁺ forms more easily. C is wrong: nuclear charge increases down the group, but shielding and distance outweigh it.
Q29Group 2 reactivity & carbonate stability · Standard · Paper 2 style · 5 marks
(a)Explain why the first ionisation energy decreases down Group 2.[3]
(b)A student heats equal amounts of calcium carbonate and barium carbonate with the same Bunsen flame and passes the gas into limewater. Predict which limewater turns milky first and state the trend shown.[2]
Show answer
(a) Outer electron further from nucleus (more shells); more shielding by inner electrons; weaker attraction despite larger nuclear charge
B1 increased atomic radius / distance. B1 increased shielding. B1 weaker attraction for the outer electron.
(b) calcium carbonate; thermal stability of carbonates increases down the group
B1 CaCO₃ first. B1 trend.
Q30Group 2 compounds & uses · Standard · Paper 2 style · 5 marks
(a)Farmers in Sindh spread calcium hydroxide (slaked lime) on acidic soil. Write an equation for the reaction of calcium hydroxide with nitric acid in the soil.[1]
(b)A field contains acid equivalent to 50.0 mol of H⁺ ions. Calculate the mass, in kg, of calcium hydroxide (Mr 74.1) needed to neutralise it. Give your answer to 3 significant figures.[2]
(c)Calcium hydroxide is made by adding water to calcium oxide, which is made from limestone. Write equations for the two steps.[2]
Show answer
(a) Ca(OH)₂ + 2HNO₃ → Ca(NO₃)₂ + 2H₂O
B1.
(b) 1.85 kg
M1 n(Ca(OH)₂) = 50.0 ÷ 2 = 25.0 mol. A1 × 74.1 = 1850 g = 1.85 kg.
(c) CaCO₃ → CaO + CO₂; CaO + H₂O → Ca(OH)₂
B1 each.
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