Chemistry 5070 · O Level
Relative masses of atoms and molecules
39 practice questions on Relative masses of atoms and molecules, with worked solutions and instant marking.
State the relative molecular mass, $M_r$, of $\text{CuSO}_4\cdot 5\text{H}_2\text{O}$?
May/June 2015
By referring to the Periodic Table for the relative atomic masses, which one has the smallest mass?
May/June 2015
By using the relative atomic masses from the Periodic Table, which one has the largest mass?
May/June 2015
Determine the relative molecular mass, $M_r$, of $\text{CuSO}_4\cdot5\text{H}_2\text{O}$?
May/June 2015
What are the mass percentages of nitrogen in ammonium nitrate, NH$_4$NO$_3$, and in calcium nitrate, Ca(NO$_3$)$_2$?
May/June 2018
A compound has a relative molecular mass of $166$. Which molecular formula could this compound have?
May/June 2018
These compounds can be used as nitrogenous fertilisers. Which compound has the smallest percentage by mass of nitrogen?
May/June 2018
What percentage by mass of nitrogen is present in ammonium nitrate, $\text{NH}_4\text{NO}_3$?
May/June 2019
Urea, a nitrogenous fertiliser, has the structure shown. What is the percentage by mass of nitrogen in it?
May/June 2019
Three nitrogen compounds and their formulae are listed: ammonia, $\text{NH}_3$; hydrazine, $\text{N}_2\text{H}_4$; hydroxylamine, $\text{NH}_2\text{OH}$. Which compound has the greatest relative molecular mass, $M_r$, and which compound has the largest percentage by mass of hydrogen?
May/June 2021
What mass, in tonnes, of aluminium oxide, $\text{Al}_2\text{O}_3$, is needed to make 27 tonnes of aluminium?
May/June 2022
For anhydrous sodium carbonate, what is the relative formula mass?
May/June 2022
The following three compounds are given: • calcium carbonate • potassium sulfate • zinc nitrate In which row is the element that makes up the largest percentage by mass in each compound shown? [$A_r$: Ca, $40$; C, $12$; O, $16$; K, $39$; S, $32$; Zn, $65$; N, $14$]
May/June 2023
The diagram illustrates the structures of the atoms of two elements, X and Z. X and Z are not the atomic symbols used for these elements. The elements combine to make a compound. What is the mass of 1 mole of this compound?
May/June 2023
Which compound has a nitrogen mass percentage of $45.2\%$? $[A_r: \text{C}, 12; \text{H}, 1; \text{N}, 14]$
May/June 2023
Which statements concerning relative atomic mass and relative molecular mass are correct?
May/June 2023
What is the relative formula mass, $M_r$, for aluminium oxide?
May/June 2024
Ammonium phosphate, $(\text{NH}_4)_3\text{PO}_4$, can be used as a fertiliser. What percentage by mass is made up of the elements that promote plant growth in ammonium phosphate?
May/June 2024
An organic compound with an $M_r$ of $88$ is given. What is its molecular formula?
May/June 2025
Hydrated sodium carbonate has the formula $\text{Na}_2\text{CO}_3\cdot10\text{H}_2\text{O}$. What is the percentage by mass of oxygen in hydrated sodium carbonate?
May/June 2025
Nitrates and ammonium salts are employed as fertilisers. Which fertiliser has the largest mass of nitrogen in $50\,\text{kg}$ of the compound? $[A_r: \text{H}, 1; \text{N}, 14; \text{O}, 16; \text{S}, 32; \text{Cl}, 35.5; \text{K}, 39]$
May/June 2025
Of the compounds, which one has the greatest relative formula mass, $M_r$? [$A_r$: $\text{K}$, $39$; $\text{N}$, $14$; $\text{O}$, $16$; $\text{Ca}$, $40$; $\text{C}$, $12$; $\text{Li}$, $7$; $\text{S}$, $32$; $\text{Mg}$, $24$; $\text{Cl}$, $35.5$]
May/June 2025
$25.0\,\text{g}$ of hydrated copper(II) sulfate crystals are heated so that anhydrous copper(II) sulfate and water vapour are produced. $\text{CuSO}_4\cdot5\text{H}_2\text{O(s)} \rightarrow \text{CuSO}_4\text{(s)} + 5\text{H}_2\text{O(g)}$ Calculate the mass of anhydrous copper(II) sulfate made. $[M_r: \text{CuSO}_4 = 160; \text{H}_2\text{O} = 18]$
Oct/Nov 2017
What are the relative formula masses for one mole of solid magnesium and one mole of chlorine gas?
Oct/Nov 2018
Iron may be obtained from the ore haematite, $\text{Fe}_2\text{O}_3$. What is the greatest mass of iron that could be formed from $500\,\text{kg}$ of haematite? $[\text{Ar}:\ \text{O}=16,\ \text{Fe}=56]$
Oct/Nov 2018
Which compound has an empirical formula with the largest relative formula mass?
Oct/Nov 2018
Which contains the largest mass of oxygen?
Oct/Nov 2020
To determine which nitrogenous fertiliser is superior, a student works out the percentage by mass of nitrogen in both ammonium sulfate and ammonium nitrate. Which row shows the correct answers?
Oct/Nov 2021
What mass of oxygen gas is needed to react completely with exactly $16\,\text{g}$ of sulfur to produce sulfur dioxide, $\text{SO}_2$?
Oct/Nov 2022
The three compounds below are given: - copper(II) nitrate, $\text{Cu(NO}_3)_2$ - zinc sulfate, $\text{ZnSO}_4$ - sodium thiosulfate, $\text{Na}_2\text{S}_2\text{O}_3$ Which row shows the element that makes up the largest percentage by mass in each compound? Relative formula masses, $M_r$: $\text{Cu(NO}_3)_2 = 188$; $\text{ZnSO}_4 = 161$; $\text{Na}_2\text{S}_2\text{O}_3 = 158$
Oct/Nov 2023
Chrome alum is the usual name for a salt with the formula $\text{CrK(SO}_4)_2$. What is the percentage by mass of chromium in chrome alum?
Oct/Nov 2023
Which row gives a pair of molecules in which the $M_r$ of compound X is exactly half the $M_r$ of compound Y? [$A_r$: C, $12$; Cl, $35.5$; H, $1$; O, $16$]
Oct/Nov 2023
Sodium phosphate, $\text{Na}_3\text{PO}_4$, and ammonium nitrate, $\text{NH}_4\text{NO}_3$, are both employed as fertilisers. Which row gives the correct percentage by mass of the element in each compound that helps plant growth?
Oct/Nov 2024
Which fertiliser has the greatest percentage by mass of nitrogen? $[M_r:\ \text{NH}_4\text{NO}_3, 80;\ (\text{NH}_4)_3\text{PO}_4, 149;\ (\text{NH}_4)_2\text{SO}_4, 132;\ (\text{NH}_2)_2\text{CO}, 60]$
Oct/Nov 2024
Iron may be obtained from the ore hematite. What is the greatest mass of iron that can be obtained from 500 kg of hematite? $[A_r: \text{O}, 16; \text{Fe}, 56]$
Oct/Nov 2024
What is ethene's relative molecular mass, $M_r$?
Oct/Nov 2024
State the relative molecular mass, $M_r$, of $\text{N}_2\text{O}$.
Oct/Nov 2024
Which one has the largest mass of oxygen?
Oct/Nov 2024
A sample containing sodium hydrogencarbonate mixed with sodium chloride is heated. The reaction equation for the decomposition of sodium hydrogencarbonate on heating is shown. $\mathrm{2NaHCO_3(s) \rightarrow Na_2CO_3(s) + CO_2(g) + H_2O(g)}$. Sodium chloride does not change when heated. If $6.0\,\mathrm{g}$ of the mixture is heated and the decrease in mass is $1.5\,\mathrm{g}$, what is the percentage by mass of sodium hydrogencarbonate in the mixture? [relative molecular mass, $M_r$: $\mathrm{NaHCO_3}$, 84; $\mathrm{Na_2CO_3}$, 106; $\mathrm{CO_2}$, 44; $\mathrm{H_2O}$, 18]
Oct/Nov 2025