Relative masses of atoms and molecules
3.2What the syllabus asks of you
- Describe relative atomic mass, Ar, as the average mass of the isotopes of an element compared to 1/12th of the mass of an atom of 12C
- Define relative molecular mass, Mr, as the sum of the relative atomic masses. Relative formula mass, Mr, will be used for ionic compounds
Read the notes first
Chapter 3: Relative masses of atoms and molecules
Drill this topic
Every question on Relative masses of atoms and molecules, untimed, marked as you go.
Make a worksheet
Choose the years and how many questions, then print it with the answers on separate pages.
15 questions
1May / June 2026 · Paper 12 · Q7Show mark scheme →
A26
B42
C52
D84
Mark scheme
2Oct / Nov 2025 · Paper 11 · Q9Show mark scheme →
AThe concentration of a solution is expressed in dm$^3$ / mol.
BThe empirical formula of a compound always gives the actual numbers of each type of atom in one molecule.
CThe molecular formula of a compound always contains more atoms than the empirical formula.
DThe relative atomic mass of an element is $\dfrac{\text{the average mass of one atom of the element}}{\frac{1}{12}\text{ the mass of one atom of carbon-12}}$.
Mark scheme
3May / June 2025 · Paper 11 · Q11Show mark scheme →
AC$_{10}$H$_{20}$O
BC$_5$H$_{10}$O
CC$_4$H$_8$O$_2$
DC$_2$H$_4$O
Mark scheme
4May / June 2025 · Paper 12 · Q9Show mark scheme →
Acalcium carbonate
Blithium sulfate
Cmagnesium chloride
Dpotassium nitrate
Mark scheme
5Oct / Nov 2024 · Paper 12 · Q7Show mark scheme →
Athe average mass of the isotopes of C and H compared to $\frac{1}{12}$ of the mass of an atom of $^{12}$C
Bthe atomic numbers of the isotopes of C and H compared to $\frac{1}{12}$ of the mass of an atom of $^{12}$C
Ctwice the $A_r$ of C plus four times the $A_r$ of H
Dtwice the $A_r$ of C plus six times the $A_r$ of H
Mark scheme
6Oct / Nov 2024 · Paper 12 · Q8Show mark scheme →
A22
B30
C44
D46
Mark scheme
7May / June 2024 · Paper 11 · Q7Show mark scheme →
A43
B75
C102
D113
Mark scheme
8May / June 2024 · Paper 12 · Q8Show mark scheme →
AIf the relative formula mass of hydrated sodium carbonate, Na2CO3•xH2O, is 286, then x is 10.
BPhosphoric(V) acid, H3PO4, has a relative molecular mass of 50.
CThe relative atomic mass of a sample of an element with isotopes of masses 20 and 22 can only be equal to 21.
DThe relative atomic mass of an element is the average mass of atoms of isotopes of the element compared with the mass of a hydrogen atom.
Mark scheme
9Oct / Nov 2023 · Paper 12 · Q7Show mark scheme →
AX: CH3CH2CH3, Y: CO2
BX: CH3CH2Cl, Y: CH2ClCH2Cl
CX: CH3CO2H, Y: CH3CH2CH3
DX: CO2, Y: CH3CO2C2H5
Mark scheme
10May / June 2023 · Paper 12 · Q8Show mark scheme →
A1 and 2 only
B1 and 3 only
C2 and 3 only
D1, 2 and 3
Mark scheme
11May / June 2022 · Paper 12 · Q13Show mark scheme →
A51
B83
C106
D124
Mark scheme
12Oct / Nov 2020 · Paper 12 · Q15Show mark scheme →
AThe concentration of a solution is expressed in dm3 / mol.
BThe empirical formula of a compound always gives the actual numbers of each type of atom in one molecule.
CThe molecular formula of a compound always contains more atoms than the empirical formula.
DThe relative atomic mass of an element is \frac{\text{the average mass of one atom of the element}}{\frac{1}{12}\text{ the mass of one atom of carbon-12}}.
Mark scheme
13May / June 2020 · Paper 12 · Q14Show mark scheme →
Agap 1: atom; gap 2: $\frac{1}{6}$
Bgap 1: atom; gap 2: $\frac{1}{12}$
Cgap 1: molecule; gap 2: $\frac{1}{6}$
Dgap 1: molecule; gap 2: $\frac{1}{12}$
Mark scheme
14Oct / Nov 2018 · Paper 11 · Q10Show mark scheme →
Amagnesium 12, chlorine 17
Bmagnesium 24, chlorine 35.5
Cmagnesium 24, chlorine 71
Dmagnesium 48, chlorine 71
Mark scheme
15May / June 2018 · Paper 12 · Q11Show mark scheme →
AC4H3O2
BC6H4O4
CC6H8O2
DC8H6O4
Mark scheme