Formulae
3.1What the syllabus asks of you
- State the formulae of the elements and compounds named in the subject content
- Define the molecular formula of a compound as the number and type of different atoms in one molecule
- Define the empirical formula of a compound as the simplest whole number ratio of the different atoms or ions in a compound
- Deduce the formula of a simple compound from the relative numbers of atoms or ions present in a model or a diagrammatic representation
- Deduce the formula of an ionic compound from the charges on the ions
- Construct word equations, symbol equations and ionic equations to show how reactants form products, including state symbols
- Deduce the symbol equation with state symbols for a chemical reaction, given relevant information
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Chapter 3: Formulae
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36 questions
1May / June 2026 · Paper 11 · Q8Show mark scheme →
Athe number and type of different atoms or ions in one mole of the compound
Bthe number of different atoms or ions in one mole of the compound
Cthe relative number of bonds between the different atoms or ions in the compound
Dthe simplest whole number ratio of the different atoms or ions in the compound
Mark scheme
2May / June 2026 · Paper 12 · Q6Show mark scheme →
ACHO
BC2H4O
CC4H8O2
DCH3COOCH2CH3
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3Oct / Nov 2025 · Paper 11 · Q8Show mark scheme →
Aempirical formula: AlSO$_4$; ionic formula: Al$^{3+}$SO$_4^{2-}$
Bempirical formula: Al$_2$S$_2$O$_8$; ionic formula: Al$^{3+}$(SO$_4^{2-}$)$_2$
Cempirical formula: Al$_2$S$_3$O$_{12}$; ionic formula: Al$^{3+}$$_2$(SO$_4$)$^{2-}$$_3$
Dempirical formula: Al$_3$S$_2$O$_8$; ionic formula: Al$^{2+}$$_3$(SO$_4^{3-}$)$_2$
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4Oct / Nov 2025 · Paper 12 · Q7Show mark scheme →
ACaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
BCaCO3(s) + 2H+(aq) → Ca2+(aq) + H2O(l) + CO2(g)
CCa2+(aq) + CO3^2–(aq) + 2H+(aq) → Ca2+(aq) + H2O(l) + CO2(g)
DCO3^2–(aq) + 2H+(aq) → H2O(l) + CO2(g)
Mark scheme
5Oct / Nov 2025 · Paper 12 · Q21Show mark scheme →
AXCl
BXCl₂
CXCl₄
DX₂Cl
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6May / June 2025 · Paper 11 · Q9Show mark scheme →
ACa2PO4
BCa(PO4)3
CCa2(PO4)3
DCa3(PO4)2
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7May / June 2025 · Paper 11 · Q10Show mark scheme →
AMg + CuSO4 → Cu + MgSO4
BMg + Cu2SO4 → 2Cu + MgSO4
C2Mg + CuSO4 → Cu + Mg2SO4
D2Mg + Cu2SO4 → 2Cu + Mg2SO4
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8Oct / Nov 2024 · Paper 11 · Q7Show mark scheme →
AKCrSO4
BKCr(SO4)2
CKCr(SO4)3
DK2Cr(SO4)3
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9Oct / Nov 2024 · Paper 11 · Q23Show mark scheme →
AZO
BZ2O2
CZO3
DZ2O
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10May / June 2024 · Paper 11 · Q6Show mark scheme →
AThe empirical and molecular formulae of a compound are always different.
BThe empirical formulae of ethyne, C2H2, and of benzene, C6H6, are the same.
CThe molecular formula always shows the simplest whole-number ratio of the different atoms or ions in a compound.
DThe empirical formula always shows the numbers and types of different atoms in one molecule of a compound.
Mark scheme
11May / June 2024 · Paper 12 · Q7Show mark scheme →
AZn2O
BZnO
CZn2O3
DZnO2
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12Oct / Nov 2023 · Paper 11 · Q7Show mark scheme →
A
B
C
D
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13Oct / Nov 2023 · Paper 11 · Q38Show mark scheme →
A1, 2 and 3
B1 only
C2 and 3 only
D3 and 4
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14Oct / Nov 2023 · Paper 12 · Q6Show mark scheme →
APb2+(aq) + 2HCl(aq) → PbCl2(s) + 2H+(aq)
BPb2+(aq) + 2HCl(aq) + 2HNO3(aq) → PbCl2(s) + 4H+(aq) + 2NO3−(aq)
CPb2+(aq) + 2Cl−(aq) → PbCl2(s)
DPb(NO3)2(aq) + 2HCl(aq) → Pb2+(aq) + 2Cl−(aq) + 2HNO3(aq)
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15May / June 2023 · Paper 12 · Q7Show mark scheme →
ANaCO3 + H2NO3 → NaNO3 + H2O + CO2
BNaCO3 + 2HNO3 → NaNO3 + H2O + CO2
CNa2CO3 + H2NO3 → Na2NO3 + H2O + CO2
DNa2CO3 + 2HNO3 → 2NaNO3 + H2O + CO2
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16May / June 2023 · Paper 12 · Q28Show mark scheme →
ACu(s) + O2(g) → 2CuO(s)
BMg(s) + H2SO4(aq) → MgSO4(aq) + H2(g)
CNa(s) + H2O(l) → NaO(aq) + H2(g)
D2Zn(s) + 2HNO3(aq) → 2ZnNO3(aq) + H2(g)
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17Oct / Nov 2022 · Paper 12 · Q12Show mark scheme →
ACO2 + Mg(OH)2 → MgCO3 + H2O
BCO2 + 2Mg(OH)2 → 2MgCO3 + 2H2O
C2CO2 + Mg(OH)2 → MgCO3 + H2O
D2CO2 + Mg(OH)2 → 2MgCO3 + H2O
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18Oct / Nov 2022 · Paper 12 · Q14Show mark scheme →
Abutanol, C4H10O
Bhydrogen peroxide, H2O2
Cnitrogen dioxide, NO2
Dwater, H2O
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19Oct / Nov 2022 · Paper 12 · Q37Show mark scheme →
A4 6 5
B5 4 6
C5 6 4
D6 4 5
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20May / June 2022 · Paper 11 · Q12Show mark scheme →
A2
B3
C4
D5
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21May / June 2022 · Paper 12 · Q12Show mark scheme →
A2AgNO3(aq) + K2CrO4(aq) → Ag2CrO4(s) + 2KNO3(aq)
B2Ag+(aq) + 2NO3–(aq) + 2K+(aq) + CrO4^2–(aq) → Ag2CrO4(s) + 2NO3–(aq) + 2K+(aq)
C2Ag+(aq) + CrO4^2–(aq) → Ag2CrO4(s)
DAg+(aq) + CrO4–(aq) → AgCrO4(s)
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22May / June 2022 · Paper 12 · Q38Show mark scheme →
Amethanol
Bmethanoic acid
Cethanol
Dethanoic acid
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23Oct / Nov 2021 · Paper 12 · Q9Show mark scheme →
AH-C(=O)-O-H
BH-C(H)(H)-C(=O)-O-H
CH-C(H)(H)-C(H)=O
DH-C(H)(H)-C(H)(H)-C(=O)-O-H
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24May / June 2021 · Paper 11 · Q9Show mark scheme →
ACH$_2$
BC$_2$H$_4$
CC$_5$H$_{10}$
DC$_n$H$_{2n}$
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25May / June 2021 · Paper 11 · Q12Show mark scheme →
A2
B4
C10
D15
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26Oct / Nov 2020 · Paper 12 · Q13Show mark scheme →
AMg + CuSO4 → Cu + MgSO4
BMg + Cu2SO4 → 2Cu + MgSO4
C2Mg + CuSO4 → Cu + Mg2SO4
D2Mg + Cu2SO4 → 2Cu + Mg2SO4
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27May / June 2020 · Paper 12 · Q13Show mark scheme →
As, aq, aq, aq, g
Bs, l, aq, l, g
Cs, l, l, aq, g
Ds, aq, aq, l, g
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28May / June 2019 · Paper 12 · Q10Also set in May / June 2019 Paper 11Show mark scheme →
ACaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
BCa2+(aq) + CO3^2–(aq) + 2H+(aq) → Ca2+(aq) + H2O(l) + CO2(g)
CCO3^2–(aq) + 2H+(aq) → H2O(l) + CO2(g)
DCaCO3(s) + 2H+(aq) → Ca2+(aq) + H2O(l) + CO2(g)
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29May / June 2019 · Paper 12 · Q26Show mark scheme →
AX$_2$Cl
BXCl
CXCl$_2$
DXCl$_4$
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30May / June 2019 · Paper 12 · Q37Also set in May / June 2019 Paper 11Show mark scheme →
ACH2O
BCH4O
CC2H3O
DC2H4O2
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31Oct / Nov 2018 · Paper 12 · Q10Show mark scheme →
A2
B3
C4
D5
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32Oct / Nov 2018 · Paper 12 · Q35Show mark scheme →
AC2H6
BC4H10
CC5H10
DC6H6
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33Oct / Nov 2017 · Paper 11 · Q31Show mark scheme →
AW 1, X 8, Y 8, Z 9
BW 1, X 17, Y 8, Z 9
CW 2, X 16, Y 8, Z 9
DW 2, X 25, Y 16, Z 18
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34Oct / Nov 2016 · Paper 11 · Q31Show mark scheme →
AZCl2
BZ2Cl
CZ2Cl7
DZ7Cl2
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35Oct / Nov 2016 · Paper 12 · Q8Show mark scheme →
APb⁺ + I⁻ → PbI
BPb⁺ + 2I⁻ → PbI₂
CPb²⁺ + I⁻ → PbI
DPb²⁺ + 2I⁻ → PbI₂
Mark scheme
36May / June 2016 · Paper 12 · Q9Show mark scheme →
AC2H4O
BC4H8O2
CC6H12O3
DC8H16O4
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