Formulae

A sample of an iron oxide contains $50.4\,\text{g}$ of iron and $21.6\,\text{g}$ of oxygen. Determine the empirical formula of the iron oxide.

Feb/March 2018

Lime is produced by heating limestone. Which equation shows this reaction?

Feb/March 2019

A nitrogen oxide contains the following percentages by mass: N, 30.4%; O, 69.6%. Its relative molecular mass is 92. Determine the molecular formula of this nitrogen oxide.

Feb/March 2019

Methane, $\text{CH}_4$, reacts with air to produce carbon dioxide and water. What balanced equation represents this reaction?

Feb/March 2020

A hydrocarbon has the formula $\text{C}_x\text{H}_y$. Its complete combustion equation is given below. $\text{C}_x\text{H}_y + 8\text{O}_2 \rightarrow 5\text{CO}_2 + 6\text{H}_2\text{O}$ What are the values of $x$ and $y$?

Feb/March 2021

Antifreeze is made from a blend of water and ethylene glycol. Their displayed formulae are shown in the diagram. What is the molecular formula for ethylene glycol?

Feb/March 2025

Which row gives the formula of the substance named?

Feb/March 2025

Which of the following is the correct formula for the named compound?

Feb/March 2025

A compound, X, has a mass composition of $40.0\%$ carbon, $6.7\%$ hydrogen and $53.3\%$ oxygen. Its relative molecular mass, $M_r$, is $60$. What is the molecular formula of X?

May/June 2016

An analysis of a compound made from magnesium and nitrogen found that it contained $14.4\,\text{g}$ of magnesium and $5.6\,\text{g}$ of nitrogen. Determine the empirical formula of the compound.

May/June 2016

Aluminium undergoes reaction with fluorine. $x\text{Al}(s) + y\text{F}_2(g) \rightarrow z\text{AlF}_3(s)$ What values of $x$, $y$ and $z$ make the equation balanced?

May/June 2017

Which of these equations are balanced? 1. $\text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2$ 2. $\text{ZnCO}_3 + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{CO}_2 + 2\text{H}_2\text{O}$ 3. $\text{Mg(NO}_3)_2 + \text{NaOH} \rightarrow \text{Mg(OH)}_2 + 2\text{NaNO}_3$ 4. $\text{CaCO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{CaSO}_4 + \text{H}_2\text{O} + \text{CO}_2$

May/June 2017

Propane reacts with oxygen. $\text{C}_3\text{H}_8 + x\text{O}_2 \rightarrow 3\text{CO}_2 + y\text{H}_2\text{O}$. What values of $x$ and $y$ make the equation balanced?

May/June 2019

An aluminium reaction is shown. $\;x\text{Al} + y\text{O}_2 + 6\text{H}_2\text{O} \rightarrow x\text{Al(OH)}_3$ What values of $x$ and $y$ make the equation balanced?

May/June 2021

An NPK fertiliser is produced by combining two compounds. The first compound has the formula $(\text{NH}_4)_2\text{HPO}_4$. State the formula of the second compound.

May/June 2021

An equation for a reaction of aluminium is given below. $x\text{Al} + y\text{O}_2 + 6\text{H}_2\text{O} \rightarrow x\text{Al(OH)}_3$ What are the values of $x$ and $y$ that make the equation balanced?

May/June 2021

A molecule of compound P has two carbon atoms and four hydrogen atoms. Which row shows P?

May/June 2022

Which equation correctly shows the decomposition of calcium nitrate?

May/June 2022

When sodium burns in oxygen, sodium oxide is formed. What balanced equation represents this reaction?

May/June 2023

Which formula counts as an empirical formula?

May/June 2023

Which row gives the correct formulae for lead(II) bromide and butane?

May/June 2024

Calcium phosphate is produced when solutions of calcium chloride and sodium phosphate are mixed together. $x\,\text{CaCl}_2 + y\,\text{Na}_3\text{PO}_4 \rightarrow 2\text{Ca}_3(\text{PO}_4)_2 + 12\text{NaCl}$. What are the values of $x$ and $y$ that balance the equation?

May/June 2024

Which statement gives the correct definition of molecular formula?

May/June 2024

The incomplete equation for photosynthesis is given below. $w\text{CO}_2 + x\text{H}_2\text{O} \rightarrow \text{P} + y\text{O}_2$ Compound P is one of the products formed in the reaction. Which row states the values of $w$, $x$ and $y$ and also gives the empirical formula of compound P?

May/June 2024

Which row gives the correct formula for the substance named?

May/June 2025

Which statement gives the description of a hydrated salt?

May/June 2025

The formulae for two hydrated salts are given. • $\text{CuSO}_4 \cdot x\text{H}_2\text{O}$ • $\text{CoCl}_2 \cdot y\text{H}_2\text{O}$ State the values of $x$ and $y$.

May/June 2025

Three organic molecules are given below. The molecular formula of propanoic acid is $\text{CH}_3\text{CH}_2\text{COOH}$. The molecular formula of lactic acid is $\text{CH}_3\text{CH(OH)COOH}$. A glucose molecule contains only $6$ carbon atoms, $6$ oxygen atoms and $12$ hydrogen atoms. Which molecules have the same empirical formula?

May/June 2025

Aluminium reacts with iron(III) oxide to produce aluminium oxide and iron. Which chemical equation for the reaction between aluminium and iron(III) oxide is correct?

May/June 2025

An analysis of a compound shows that it contains only $85.7\%$ carbon and $14.3\%$ hydrogen. What is the empirical formula?

May/June 2025

A molecule of X is made up of two carbon atoms, four hydrogen atoms and two oxygen atoms. What is the formula of X?

Oct/Nov 2016

X is made up of two bromine atoms, three carbon atoms, six hydrogen atoms and one oxygen atom in each molecule. What is the formula of X?

Oct/Nov 2016

Which elements are present in the compound BaCO$_3$?

Oct/Nov 2016

An analysis shows that a compound contains $85.7\%$ carbon and $14.3\%$ hydrogen. What empirical formula does it have?

Oct/Nov 2017

The chemical equation for the reaction of phosphorus with oxygen is given below. $x\text{P}_4 + y\text{O}_2 \rightarrow z\text{P}_2\text{O}_5$ What values of $x$, $y$ and $z$ are needed to balance the equation?

Oct/Nov 2017

The relative molecular mass of an alcohol is $88$. Its percentage composition by mass is given as: C, $54.5\%$; H, $9.1\%$; O, $36.4\%$. Which row gives the empirical formula and molecular formula of this alcohol?

Oct/Nov 2017

Which compound corresponds to silicon(IV) oxide?

Oct/Nov 2017

A compound is composed of $34.5\%$ calcium, $24.1\%$ silicon and $41.4\%$ oxygen by mass. What is the empirical formula of this compound?

Oct/Nov 2017

Calcium phosphate is produced when solutions of calcium chloride and sodium phosphate are mixed and react. $x\text{CaCl}_2 + y\text{Na}_3\text{PO}_4 \rightarrow 2\text{Ca}_3(\text{PO}_4)_2 + 12\text{NaCl$ What values of $x$ and $y$ balance the equation?

Oct/Nov 2018

Iron(III) chromate is a yellow solid composed of the ions $\text{Fe}^{3+}$ and $\text{CrO}_4^{2-}$. What is the formula for iron(III) chromate?

Oct/Nov 2018

The diagram shows the structure of a molecule. What is the formula of this molecule?

Oct/Nov 2019

The equation for the combustion of propane in air is given below. $\text{C}_3\text{H}_8(\text{g}) + x\text{O}_2(\text{g}) \rightarrow 3\text{CO}_2(\text{g}) + y\text{H}_2\text{O}(\text{g})$. What values of $x$ and $y$ make the equation balanced?

Oct/Nov 2020

How many atoms are present in a single molecule of ethanoic acid?

Oct/Nov 2020

What is the empirical formula of an iron oxide produced when 2.24 g of iron reacts with 0.96 g of oxygen?

Oct/Nov 2020

What is the empirical formula of an oxide of iron produced by reacting 2.24 g of iron with 0.96 g of oxygen?

Oct/Nov 2020

Ethyl methanoate, $\text{HCOOC}_2\text{H}_5$, is combusted in an excess of oxygen, forming carbon dioxide and water. The equation is given below. $2\text{HCOOC}_2\text{H}_5 + x\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O}$ Determine the value of $x$?

Oct/Nov 2020

Determine the empirical formula for an iron oxide produced when $2.24\text{ g}$ of iron is reacted with $0.96\text{ g}$ of oxygen.

Oct/Nov 2020

The complete combustion of methane is represented by the chemical equation below. $\text{2CH}_4 + z\text{O}_2 \rightarrow \text{2CO}_2 + \text{4H}_2\text{O}$ What is the value of $z$?

Oct/Nov 2021

An aluminium ion has the formula $\text{Al}^{3+}$. What is the formula for aluminium sulfate?

Oct/Nov 2021

Aluminium oxide is an ionic compound made up of $\text{Al}^{3+}$ ions and $\text{O}^{2-}$ ions. Aluminium hydroxide is an ionic compound made up of $\text{Al}^{3+}$ ions and $\text{OH}^-$ ions. Which row shows the correct formulae for aluminium oxide and aluminium hydroxide?

Oct/Nov 2021

The formulae below are provided. CaCO$_3$ CaO Cl$_2$ CH$_4$ C$_2$H$_5$OH C$_2$H$_6$ CuSO$_4$ H$_2$ H$_2$O MgO NaCl SO$_2$ Use these formulae to answer the questions that follow. Each formula can be chosen once, more than once, or not used at all. State which formula stands for:

Oct/Nov 2021

Identify which of the following equations are balanced. 1. $\text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2$ 2. $\text{ZnCO}_3 + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{CO}_2 + 2\text{H}_2\text{O}$ 3. $\text{Mg(NO}_3)_2 + \text{NaOH} \rightarrow \text{Mg(OH)}_2 + 2\text{NaNO}_3$ 4. $\text{CaCO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{CaSO}_4 + \text{H}_2\text{O} + \text{CO}_2$

Oct/Nov 2023

Which of these equations are balanced?

Oct/Nov 2023

Which row gives the formulae for sodium carbonate, zinc nitrate and ammonium sulfate?

Oct/Nov 2023

By mass, a hydrocarbon is $85.7\%$ carbon. State the empirical formula of the hydrocarbon.

Oct/Nov 2023

The amounts, in moles, of atoms $X$, $Y$ and $Z$ present in a compound are given. What is the formula of the compound?

Oct/Nov 2023

What is the empirical formula of a compound containing $3.66\,\text{g}$ of hydrogen, $37.8\,\text{g}$ of phosphorus and $58.5\,\text{g}$ of oxygen?

Oct/Nov 2024

Which row identifies hydrated copper(II) sulfate and states its formula?

Oct/Nov 2024

Ammonium iron(III) citrate has these ions in its formula: • more than one ammonium ion • one iron ion • two $\text{C}_6\text{H}_4\text{O}_7^{4-}$ ions. What is the chemical formula of ammonium iron(III) citrate?

Oct/Nov 2024

Iron(III) chloride, $\text{FeCl}_3$, is a brown solid. What does (III) in the name indicate?

Oct/Nov 2025

Which statement gives the definition of the term molecular formula?

Oct/Nov 2025

The molecular formulae for four compounds are shown below. 1. $\mathrm{CH_4}$ 2. $\mathrm{C_2H_6}$ 3. $\mathrm{C_3H_8}$ 4. $\mathrm{C_3H_6}$ Which of these molecular formulae are also the empirical formulae of the compounds?

Oct/Nov 2025

A compound is made up of 40.0% carbon, 6.7% hydrogen and 53.3% oxygen only. The relative molecular mass, $M_r$, of the compound is 60. Which row gives the empirical formula and the molecular formula of the compound?

Oct/Nov 2025

Which compound has an empirical formula identical to its molecular formula?

Oct/Nov 2025