Identification of ions and gases
12.5What the syllabus asks of you
- Describe tests to identify the anions: (a) carbonate, CO3 2–, by reaction with dilute acid and then testing for carbon dioxide gas (b) chloride, Cl –, bromide, Br –, and iodide, I–, by acidifying with dilute nitric acid then adding aqueous silver nitrate (c) nitrate, NO3 –, by reduction with aluminium foil and aqueous sodium hydroxide and then testing for ammonia gas (d) sulfate, SO4 2–, by acidifying with dilute nitric acid then adding aqueous barium nitrate (e) sulfite, SO3 2–, by reaction with acidified aqueous potassium manganate(VII)
- Describe tests using aqueous sodium hydroxide and aqueous ammonia to identify the aqueous cations: (a) aluminium, Al 3+ (b) ammonium, NH4 + (c) calcium, Ca2+ (d) chromium(III), Cr3+ (e) copper(II), Cu2+ (f) iron(II), Fe2+ (g) iron(III), Fe3+ (h) zinc, Zn2+
- Describe tests to identify the gases: (a) ammonia, NH3, using damp red litmus paper (b) carbon dioxide, CO2, using limewater (c) chlorine, Cl 2, using damp litmus paper (d) hydrogen, H2, using a lighted splint (e) oxygen, O2, using a glowing splint (f) sulfur dioxide, SO2, using acidified aqueous potassium manganate(VII)
- Describe the use of a flame test to identify the cations: (a) lithium, Li+ (b) sodium, Na+ (c) potassium, K+ (d) calcium, Ca2+ (e) barium, Ba2+ (f) copper(II), Cu2+
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Chapter 12: Identification of ions and gases
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42 questions
1May / June 2026 · Paper 11 · Q40Show mark scheme →
AFe3+ and NH4+
BFe3+ and NO3–
CFe2+ and NH4+
DFe2+ and NO3–
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2May / June 2026 · Paper 12 · Q40Show mark scheme →
ANH$_4^+$ and SO$_3^{2-}$
BAl$^{3+}$ and NO$_3^-$
CCa$^{2+}$ and NO$_3^-$
DZn$^{2+}$ and SO$_3^{2-}$
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3Oct / Nov 2025 · Paper 11 · Q40Show mark scheme →
AAl3+
BCa2+
CCu2+
DNH4+
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4Oct / Nov 2025 · Paper 12 · Q39Show mark scheme →
AThe cation in J must be Al3+.
BThe cation in J must be Fe2+.
CWhen dilute nitric acid and then aqueous barium nitrate are added to an aqueous solution of J, a white precipitate is formed.
DWhen dilute nitric acid and then aqueous silver nitrate are added to an aqueous solution of J, a white precipitate is formed.
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5Oct / Nov 2025 · Paper 12 · Q40Show mark scheme →
Aammonium carbonate
Bammonium nitrate
Ccalcium carbonate
Dcalcium nitrate
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6May / June 2025 · Paper 11 · Q40Show mark scheme →
AP: K⁺ and SO₄²⁻; Q: Cr³⁺ and CO₃²⁻
BP: K⁺ and CO₃²⁻; Q: Fe²⁺ and SO₄²⁻
CP: K⁺ and CO₃²⁻; Q: Cr³⁺ and SO₄²⁻
DP: Li⁺ and CO₃²⁻; Q: Cr³⁺ and SO₄²⁻
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7May / June 2025 · Paper 12 · Q40Show mark scheme →
Aaluminium chloride
Baluminium sulfate
Ccalcium chloride
Dcalcium sulfate
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8Oct / Nov 2024 · Paper 11 · Q40Show mark scheme →
Aaluminium ✓, ammonium ✗, zinc ✓
Baluminium ✓, ammonium ✓, zinc ✗
Caluminium ✗, ammonium ✗, zinc ✓
Daluminium ✗, ammonium ✓, zinc ✗
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9Oct / Nov 2024 · Paper 12 · Q40Show mark scheme →
Aammonium chloride
Bammonium nitrate
Cbarium chloride
Dbarium nitrate
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10May / June 2024 · Paper 11 · Q40Show mark scheme →
ACa2+ and Br– ; Na+ and NO3–
BCa2+ and Cl– ; Na+ and I–
CCa2+ and Cl– ; Li+ and NO3–
DCa2+ and Cl– ; Na+ and NO3–
Mark scheme
11Oct / Nov 2023 · Paper 11 · Q40Show mark scheme →
Aexperiment 1: blue, experiment 2: blue
Bexperiment 1: blue, experiment 2: red
Cexperiment 1: red, experiment 2: blue
Dexperiment 1: red, experiment 2: red
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12Oct / Nov 2023 · Paper 12 · Q40Show mark scheme →
AAl$^{3+}$
BCa$^{2+}$
CFe$^{2+}$
DZn$^{2+}$
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13May / June 2023 · Paper 12 · Q40Show mark scheme →
ACr3+ ; NH4+
BCu2+ ; CO3 2–
CFe2+ ; CO3 2–
DFe3+ ; NH4+
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14Oct / Nov 2022 · Paper 11 · Q3Show mark scheme →
AHCl(aq) and AgNO3
BH2SO4(aq) and Ba(NO3)2
CNaOH(aq) and CuSO4
DNaOH(aq) and ZnSO4
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15Oct / Nov 2022 · Paper 12 · Q3Show mark scheme →
Aammonium, chromium(III), sulfate
Bammonium, iron(II), sulfate
Cchromium(III), carbonate, sulfate
Diron(II), nitrate, sulfate
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16May / June 2022 · Paper 11 · Q3Show mark scheme →
AThe anion present is Cl$^-$.
BThe anion present is not Cl$^-$.
CThe cation present is Al$^{3+}$.
DThe cation present is Zn$^{2+}$.
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17May / June 2022 · Paper 12 · Q3Show mark scheme →
AX contains only aluminium sulfate, Al2(SO4)3.
BX contains only calcium sulfite, CaSO3.
CX must contain aluminium sulfite, Al2(SO3)3, or zinc sulfite, ZnSO3.
DX must contain aluminium sulfite, Al2(SO3)3, calcium sulfite, CaSO3, or zinc sulfite, ZnSO3.
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18Oct / Nov 2021 · Paper 11 · Q5Show mark scheme →
A1, 2 and 3
B1 and 3 only
C3 only
D2 and 4
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19Oct / Nov 2021 · Paper 12 · Q5Show mark scheme →
Achromium(III) sulfate
Bchromium(III) chloride
Ciron(III) chloride
Diron(III) sulfate
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20Oct / Nov 2021 · Paper 12 · Q6Also set in Oct / Nov 2021 Paper 11, May / June 2017 Paper 11, May / June 2017 Paper 12Show mark scheme →
Aacidified aqueous barium nitrate; forms a white precipitate
Baqueous ammonia; forms a white precipitate, soluble in excess of the reagent
Caqueous sodium hydroxide; forms a white precipitate, insoluble in excess of the reagent
Dpowdered copper; forms a grey precipitate
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21May / June 2021 · Paper 11 · Q4Show mark scheme →
AFe3+ and NH4+
BFe3+ and NO3–
CFe2+ and NH4+
DFe2+ and NO3–
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22May / June 2021 · Paper 12 · Q4Show mark scheme →
AThe cation in J must be Al³⁺.
BThe cation in J must be Fe²⁺.
CWhen dilute nitric acid and aqueous barium nitrate are added to an aqueous solution of J, a white precipitate is formed.
DWhen dilute nitric acid and aqueous silver nitrate are added to an aqueous solution of J, a white precipitate is formed.
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23May / June 2021 · Paper 12 · Q5Also set in May / June 2021 Paper 11Show mark scheme →
Aammonia
Bchlorine
Chydrogen
Doxygen
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24Oct / Nov 2020 · Paper 11 · Q5Show mark scheme →
Aammonium carbonate
Bsodium sulfate
Ccalcium nitrate
Dzinc chloride
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25Oct / Nov 2020 · Paper 12 · Q5Show mark scheme →
AAqueous ammonia gives a white precipitate which is soluble in excess reagent.
BCopper turnings give a precipitate of zinc.
CAcidified aqueous silver nitrate gives a yellow precipitate.
DAcidified aqueous barium nitrate gives a white precipitate.
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26Oct / Nov 2020 · Paper 12 · Q6Also set in Oct / Nov 2020 Paper 11Show mark scheme →
AAl³⁺(aq)
BCa²⁺(aq)
CCu²⁺(aq)
DNa⁺(aq)
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27May / June 2020 · Paper 11 · Q4Show mark scheme →
Atest-tube 1: aqueous sodium hydroxide; test-tube 2: aqueous ammonia; test-tube 3: dilute hydrochloric acid and aqueous silver nitrate
Btest-tube 1: aqueous sodium hydroxide; test-tube 2: dilute nitric acid and aqueous silver nitrate; test-tube 3: dilute hydrochloric acid
Ctest-tube 1: aqueous ammonia; test-tube 2: dilute nitric acid and aqueous silver nitrate; test-tube 3: nitric acid and barium nitrate
Dtest-tube 1: aqueous sodium hydroxide; test-tube 2: aqueous ammonia; test-tube 3: dilute nitric acid and aqueous silver nitrate
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28May / June 2020 · Paper 11 · Q15Show mark scheme →
A0.01 mol of a white hydroxide and 0.01 mol of a blue hydroxide
B0.01 mol of a white hydroxide
C0.01 mol of a blue hydroxide
Dno solid residue
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29May / June 2020 · Paper 12 · Q4Show mark scheme →
Aexperiment 1: ✓ ; experiment 2: ✓
Bexperiment 1: ✓ ; experiment 2: ✗
Cexperiment 1: ✗ ; experiment 2: ✓
Dexperiment 1: ✗ ; experiment 2: ✗
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30Oct / Nov 2019 · Paper 11 · Q3Show mark scheme →
AExcess aqueous barium nitrate is added to aqueous sodium chloride.
BExcess aqueous sodium hydroxide is added to aqueous aluminium chloride.
CExcess aqueous sodium hydroxide is added to aqueous iron(II) sulfate.
DExcess hydrochloric acid is added to aqueous silver nitrate.
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31Oct / Nov 2019 · Paper 12 · Q20Also set in Oct / Nov 2019 Paper 11Show mark scheme →
AIt is a colourless, odourless gas.
BIt is a gas that turns damp blue litmus paper red.
CIt is formed when potassium nitrate is heated with aqueous sodium hydroxide and aluminium.
DIt is manufactured using vanadium(V) oxide as a catalyst.
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32May / June 2019 · Paper 12 · Q2Also set in May / June 2019 Paper 11Show mark scheme →
Acalcium iodide
Bcopper(II) chloride
Clead(II) iodide
Dsodium chloride
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33Oct / Nov 2018 · Paper 12 · Q3Also set in Oct / Nov 2018 Paper 11Show mark scheme →
Acalcium iodide
Bcopper(II) chloride
Ciron(II) iodide
Dsodium chloride
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34May / June 2018 · Paper 11 · Q3Show mark scheme →
ACr3+ and Cl–
BCr3+ and SO4 2–
CFe2+ and Cl–
DFe2+ and SO4 2–
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35May / June 2018 · Paper 12 · Q3Show mark scheme →
Adamp blue litmus paper; acidified potassium manganate(VII)
Bdamp blue litmus paper; damp red litmus paper
Cdamp red litmus paper; acidified potassium manganate(VII)
Ddamp red litmus paper; damp blue litmus paper
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36Oct / Nov 2017 · Paper 12 · Q2Also set in Oct / Nov 2017 Paper 11Show mark scheme →
AAl³⁺
BCa²⁺
CCu²⁺
DZn²⁺
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37May / June 2017 · Paper 11 · Q1Show mark scheme →
Aammonia
Bchlorine
Chydrogen
Doxygen
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38Oct / Nov 2016 · Paper 11 · Q2Show mark scheme →
Aexperiment 1: blue, experiment 2: blue
Bexperiment 1: blue, experiment 2: red
Cexperiment 1: red, experiment 2: blue
Dexperiment 1: red, experiment 2: red
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39Oct / Nov 2016 · Paper 12 · Q11Show mark scheme →
Aaluminium
Bcalcium
Ccopper(II)
Dzinc
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40Oct / Nov 2016 · Paper 12 · Q25Show mark scheme →
Acopper(II) chloride
Bcopper(II) sulfate
Ciron(II) chloride
Diron(II) sulfate
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41May / June 2016 · Paper 11 · Q2Show mark scheme →
Aammonia
Bchlorine
Chydrogen chloride
Doxygen
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42May / June 2016 · Paper 12 · Q1Show mark scheme →
Agas: Cl2; test: damp litmus paper; observation: the litmus paper turns blue
Bgas: NH3; test: damp litmus paper; observation: the litmus paper turns red
Cgas: O2; test: limewater; observation: no change is observed
Dgas: SO2; test: acidified aqueous potassium manganate(VII); observation: the colour of the solution changes from purple to colourless
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