Formulae

An organic compound is represented by the molecular formula $\text{C}_8\text{H}_{16}\text{O}_4$. Determine the empirical formula of this compound.

May/June 2016

On heating zinc in air, it reacts with oxygen to produce an oxide. A student carries out an experiment to determine the formula of zinc oxide.

May/June 2016

A compound is made up of $70\%$ iron by mass and $30\%$ oxygen by mass. What is the empirical formula of this compound? [$A_r$: O, $16$; Fe, $56$]

May/June 2017

What empirical formula does ethanoic acid have?

May/June 2019

W is a compound made up of carbon, hydrogen and oxygen.

May/June 2019

The empirical formula of compound X is $\text{CH}_2$ and the relative molecular mass, $M_r$, of X is $70$. What is the molecular formula for X?

May/June 2021

The relative molecular mass, $M_r$, of liquid Z is 60. Z is made up of 40.0% carbon, 6.70% hydrogen and 53.3% oxygen. Which row gives the correct empirical formula and molecular formula of Z?

May/June 2022

Two statements are provided. statement 1: The mass percentage of carbon is higher in methane than in butane. statement 2: Butane is one of two isomers that have the molecular formula $\text{C}_4\text{H}_{10}$. Which of these statements are correct?

May/June 2022

Which equation is the correct one?

May/June 2023

A sample of substance X is made up of iron and sulfur only. $[A_r: \text{Fe},\,56;\,\text{S},\,32]$ In which row could both statements about X be correct?

May/June 2024

Several statements concerning empirical and molecular formulae are provided. Which one is correct?

May/June 2024

Which statement concerning water of crystallisation is correct?

May/June 2024

What formula represents zinc oxide?

May/June 2024

By mass, compound $Q$ consists of $40.00\%$ carbon, $6.67\%$ hydrogen and $53.33\%$ oxygen. [$A_r$: $\text{C}$, $12$; $\text{H}$, $1$; $\text{O}$, $16$]

Oct/Nov 2015

A compound, T, is composed by mass of $41.0\%$ potassium, $33.7\%$ sulfur and $25.3\%$ oxygen. [$A_r$: K, $39$; S, $32$; O, $16$]

Oct/Nov 2015

A compound made up solely of carbon and hydrogen contains $80.0\%$ carbon by mass. Determine its empirical formula?

Oct/Nov 2016

A student determines that a compound has $4.8\text{ g}$ of carbon, $0.8\text{ g}$ of hydrogen and $6.4\text{ g}$ of oxygen. $[A_r: \text{C}, 12; \text{H}, 1; \text{O}, 16]$

Oct/Nov 2016

A student combusts $4.8\,\text{g}$ of an element $X$ in excess oxygen. The mass of the oxide formed is $8.0\,\text{g}$. [$A_r: X,\,24;\,O,\,16$]

Oct/Nov 2016

A liquid compound has the empirical formula $\text{C}_2\text{H}_4\text{O}$. In order to determine the empirical formula, it is necessary to know

Oct/Nov 2017

Octane, $\text{C}_8\text{H}_{18}$, is a hydrocarbon that burns by combustion in a petrol engine. $\ldots w\,\text{C}_8\text{H}_{18} + \ldots x\,\text{O}_2 \rightarrow \ldots y\,\text{CO}_2 + \ldots z\,\text{H}_2\text{O}$ Which row contains the numbers required to balance the equation?

Oct/Nov 2017

The empirical formula of a liquid compound is $\text{C}_2\text{H}_4\text{O}$. In order to determine the empirical formula, it is necessary to know

Oct/Nov 2017

By mass, a compound is made up of $40.0\%$ carbon, $6.7\%$ hydrogen and $53.3\%$ oxygen. Its relative molecular mass falls between 55 and 65. What is the molecular formula of this compound?

Oct/Nov 2018

A section of the Periodic Table is shown containing four elements, W, X, Y and Z. These are not the elements’ true symbols. Some of these pairs of elements may react to produce compounds. Which formulae are correct?

Oct/Nov 2019

X contains, by mass, $63.6\%$ nitrogen and $36.4\%$ oxygen. State the empirical formula of X.

Oct/Nov 2020

Ruthenium has atomic number $44$. One oxide of ruthenium is the black solid, X. A sample of X with mass $5.79\,\text{g}$ contains $1.39\,\text{g}$ of oxygen. Determine the empirical formula of X.

Oct/Nov 2022

Which compound has an empirical formula that differs from its molecular formula?

Oct/Nov 2022

This equation represents the reaction when butanol burns completely in air. $\text{C}_4\text{H}_9\text{OH}(l) + x\text{O}_2(g) \rightarrow y\text{CO}_2(g) + z\text{H}_2\text{O}(g)$ Determine the values of $x$, $y$ and $z$?

Oct/Nov 2022

A few compounds that may be used as fertilisers are shown below. ammonium nitrate potassium nitrate potassium phosphate sodium phosphate Three elements needed for plant growth have the atomic symbols N, P and K. For each compound, how many of these three elements are present?

Oct/Nov 2023

Compound X is made up of carbon, hydrogen and oxygen only. Its $M_r$ is $90$. In $100\,\text{g}$ of compound X, there are $40.0\,\text{g}$ of carbon and $6.7\,\text{g}$ of hydrogen. How many oxygen atoms are present in one molecule of compound X?

Oct/Nov 2024

Chrome alum is a salt made up of two different cations together with one anion. The ions present in chrome alum are $\text{K}^+$, $\text{Cr}^{3+}$ and $\text{SO}_4^{2-}$. What is the formula of this salt?

Oct/Nov 2024

Compound Z consists only of carbon, hydrogen and oxygen. By mass, Compound Z is $48.65\%$ carbon and $8.11\%$ hydrogen. Determine the empirical formula of Z.

Oct/Nov 2024

Aluminium ions, $\mathrm{Al^{3+}}$, react with sulfate ions, $\mathrm{SO_4^{2-}}$, to produce aluminium sulfate. Which row gives the correct empirical formula and ionic formula for aluminium sulfate?

Oct/Nov 2025