Redox

The reaction shown below is known as the ‘thermite reaction’. $2\text{Al} + \text{Fe}_2\text{O}_3 \rightarrow 2\text{Fe} + \text{Al}_2\text{O}_3$ Which pair of substances undergoes a similar reaction?

Feb/March 2016

When petrol burns in a car engine, nitrogen monoxide is formed. The exhaust gases from the car engine are sent through a catalytic converter. Inside the catalytic converter, nitrogen monoxide reacts with carbon monoxide to produce nitrogen and carbon dioxide. Which statement is incorrect?

Feb/March 2016

In which reaction is the first substance in the equation oxidised?

Feb/March 2017

Two experiments are performed. In experiment 1, copper is heated in steam. In experiment 2, copper(II) oxide is heated with carbon. Which row gives the outcomes for experiments 1 and 2?

Feb/March 2017

Chlorine removes bromine from potassium bromide solution. $\text{Cl}_2 + 2\text{KBr} \rightarrow 2\text{KCl} + \text{Br}_2$. Which substance acts as the oxidising agent in this reaction?

Feb/March 2017

Hydrazine is a gas with molecular formula $\text{N}_2\text{H}_4$. When hydrazine burns in air, nitrogen gas and steam are formed. $\text{N}_2\text{H}_4(g) + \text{O}_2(g) \rightarrow \text{N}_2(g) + 2\text{H}_2\text{O}(g)$. Which statements are correct?

Feb/March 2017

In which equation does the underlined substance undergo oxidation?

Feb/March 2018

The ionic equation for the reaction between zinc and aqueous copper ions is given below. $\text{Zn}(s) + \text{Cu}^{2+}(aq) \rightarrow \text{Zn}^{2+}(aq) + \text{Cu}(s)$ Which statement about this reaction is correct?

Feb/March 2018

The equation shows the reaction of magnesium with carbon dioxide. $2\text{Mg} + \text{CO}_2 \rightarrow 2\text{MgO} + \text{C}$. Which statement correctly describes the change taking place in this reaction?

Feb/March 2019

The chemical reaction between magnesium and carbon dioxide is represented by the equation: $2\text{Mg} + \text{CO}_2 \rightarrow 2\text{MgO} + \text{C}$. Which statement correctly explains what occurs in this reaction?

Feb/March 2019

Which of these changes show reduction?

Feb/March 2019

In which reaction are Fe(s) ions formed when the mixture is heated?

Feb/March 2019

A vigorous reaction takes place when a mixture of chromium(III) oxide and aluminium is ignited using a magnesium fuse, as illustrated. The equation for the reaction is given below. $\text{Cr}_2\text{O}_3 + 2\text{Al} \rightarrow 2\text{Cr} + \text{Al}_2\text{O}_3$ Which substance is oxidised in the reaction?

Feb/March 2020

In which reaction does the underlined compound act as a reducing agent?

Feb/March 2020

Magnesium reacts with copper(II) oxide to form magnesium oxide and copper. Which substance acts as the oxidising agent in this reaction?

Feb/March 2021

In which equation is the underlined substance functioning as a reducing agent?

Feb/March 2023

The equations for two reactions are displayed below. equation 1: $\text{C} + \text{CO}_2 \rightarrow x\,\text{CO}$ equation 2: $2\text{C}_2\text{H}_6 + 7\text{O}_2 \rightarrow 4\text{CO}_2 + y\,\text{H}_2\text{O}$ Which row gives the value of $x$, the value of $y$ and the equations that are redox reactions?

Feb/March 2024

Silver oxide reacts with magnesium to produce silver and magnesium oxide. $\text{Ag}_2\text{O} + \text{Mg} \rightarrow 2\text{Ag} + \text{MgO}$. Which substance is oxidised in this reaction?

Feb/March 2024

In which equation does iron undergo oxidation?

Feb/March 2025

Mercury(II) oxide, $\text{HgO}$, breaks down on heating. The equation is shown. $2\text{HgO} \rightarrow 2\text{Hg} + \text{O}_2$ Why does this count as a reduction reaction?

Feb/March 2025

Nitrogen monoxide, NO, and carbon monoxide, CO, are each taken out of a car’s exhaust gases by a catalytic converter. Which statement explains how nitrogen monoxide and carbon monoxide are removed by a catalytic converter?

Feb/March 2025

The equations shown below each represent redox reactions. $\text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2$ $2\text{ZnO} + \text{C} \rightarrow 2\text{Zn} + \text{CO}_2$ $\text{Fe}_2\text{O}_3 + 2\text{Al} \rightarrow \text{Al}_2\text{O}_3 + 2\text{Fe}$ $2\text{CO} + 2\text{NO} \rightarrow 2\text{CO}_2 + \text{N}_2$ In these reactions, which oxide is oxidised?

May/June 2016

A highly vigorous reaction takes place when a mixture of chromium(III) oxide and aluminium is set alight using a magnesium fuse, as illustrated. The reaction equation is given below. $\text{Cr}_2\text{O}_3 + 2\text{Al} \rightarrow 2\text{Cr} + \text{Al}_2\text{O}_3$ Which substance is oxidised in the reaction?

May/June 2016

The diagram depicts a simple cell. Which statement about the process taking place while the cell is working is correct?

May/June 2016

Which equation shows a reduction reaction?

May/June 2016

A catalytic converter is fitted to many car exhaust systems. Which change does not take place in a catalytic converter?

May/June 2016

Which equation indicates a reduction reaction?

May/June 2016

Which equation shows a reduction reaction?

May/June 2016

Catalytic converters are used to eliminate certain gaseous pollutants from car exhaust fumes. Which gas is taken out of the fumes by oxidation?

May/June 2016

A teacher flowed hydrogen gas over copper(II) oxide that had been heated strongly. $CuO(s) + H_2(g) \rightarrow Cu(s) + H_2O(g)$

May/June 2016

The reactions shown below can take place in the air during a thunder-storm. $\text{N}_2 + \text{O}_2 \rightarrow 2\text{NO}$ $2\text{NO} + \text{O}_2 \rightarrow 2\text{NO}_2$ $\text{NO} + \text{O}_3 \rightarrow \text{NO}_2 + \text{O}_2$ Which row indicates what happens to the reactant molecules in each reaction?

May/June 2017

These reactions can take place in air during a thunder-storm. $\text{N}_2 + \text{O}_2 \rightarrow 2\text{NO}$ $2\text{NO} + \text{O}_2 \rightarrow 2\text{NO}_2$ $\text{NO} + \text{O}_3 \rightarrow \text{NO}_2 + \text{O}_2$ Which row indicates what happens to the reactant molecules in each reaction?

May/June 2017

The reactions illustrated can take place in the air during a thunderstorm. $\text{N}_2 + \text{O}_2 \rightarrow 2\text{NO}$ $2\text{NO} + \text{O}_2 \rightarrow 2\text{NO}_2$ $\text{NO} + \text{O}_3 \rightarrow \text{NO}_2 + \text{O}_2$ Which row indicates what happens to the reactant molecules in each of these reactions?

May/June 2017

A redox reaction is illustrated below. $\text{Zn} + \text{Cu}^{2+} \rightarrow \text{Zn}^{2+} + \text{Cu}$ Which statement about this reaction is correct?

May/June 2017

A redox reaction example is shown. $\text{Zn} + \text{Cu}^{2+} \rightarrow \text{Zn}^{2+} + \text{Cu}$ Which statement concerning the reaction is correct?

May/June 2017

A redox reaction is illustrated below. $\text{Zn} + \text{Cu}^{2+} \rightarrow \text{Zn}^{2+} + \text{Cu}$ Which statement concerning this reaction is correct?

May/June 2017

Which equation represents an oxidation reaction?

May/June 2018

Reaction X is used as a test for water. Reaction Y takes place in the blast furnace used to extract iron. Reaction X: $\text{CoCl}_2 + 6\text{H}_2\text{O} \rightleftharpoons \text{CoCl}_2\cdot 6\text{H}_2\text{O}$ Reaction Y: $\text{C} + \text{CO}_2 \rightarrow 2\text{CO}$ Reaction X is ......1...... . In reaction Y, the oxide $\text{CO}_2$ is ......2...... . Which words correctly fill gaps 1 and 2?

May/June 2018

Which equation represents an oxidation reaction?

May/June 2018

Which equation represents an oxidation reaction?

May/June 2018

Chlorine causes iodide ions in potassium iodide to be displaced: $\text{Cl}_2 + 2\text{I}^- \rightarrow \text{I}_2 + 2\text{Cl}^-$. Which species acts as the oxidising agent?

May/June 2018

Iron(II) chloride solution is reacted with chlorine gas. The equation is given below. $2\text{FeCl}_2(aq) + \text{Cl}_2(g) \rightarrow 2\text{FeCl}_3(aq)$ Which of these statements about this reaction are correct?

May/June 2018

The redox equation below is given. $2\text{Fe}^{3+} + \text{Zn} \rightarrow 2\text{Fe}^{2+} + \text{Zn}^{2+}$ Which of the following statements are correct?

May/June 2018

This question concerns manganese and its compounds.

May/June 2018

Within a blast furnace, iron is obtained when iron(III) oxide reacts with carbon monoxide. The equation is given below. $\text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2$ Which substance is oxidised, and which substance is reduced?

May/June 2019

These reaction types are given: 1 oxidation, 2 decomposition, 3 combustion, 4 reduction. The equation represents magnesium reacting with oxygen: $2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}$. Which of these reaction types does magnesium undergo in this reaction?

May/June 2019

Zinc is produced when zinc oxide is heated together with carbon. $\text{zinc oxide} + \text{carbon} \rightarrow \text{zinc} + \text{carbon monoxide}$. Which substance is oxidised in this reaction?

May/June 2019

Which of the following changes are oxidation? 1. $2\text{I}^- \rightarrow \text{I}_2 + 2\text{e}^-$ 2. $\text{Cr(VI)} \rightarrow \text{Cr(III)}$ 3. $\text{Fe(II)} \rightarrow \text{Fe(III)}$

May/June 2019

Zinc is obtained from the ore zinc blende by means of two chemical reactions. 1. $\text{2ZnS} + 3\text{O}_2 \rightarrow 2\text{ZnO} + 2\text{SO}_2$ 2. $\text{ZnO} + \text{C} \rightarrow \text{Zn} + \text{CO}_2$ In reactions 1 and 2, which substance undergoes reduction?

May/June 2019

The ionic equation for the reaction between aqueous potassium bromide and chlorine gas is given. $2\text{Br}^- + \text{Cl}_2 \rightarrow \text{Br}_2 + 2\text{Cl}^-$ Which statement is right?

May/June 2019

Zinc is obtained from its ore, zinc blende, by means of two chemical reactions. 1. $2\text{ZnS} + 3\text{O}_2 \rightarrow 2\text{ZnO} + 2\text{SO}_2$ 2. $2\text{ZnO} + \text{C} \rightarrow 2\text{Zn} + \text{CO}_2$ Which substance undergoes reduction in reactions 1 and 2?

May/June 2019

Which of these changes are reductions? 1. $\text{Cl}_2 + 2e^- \rightarrow 2\text{Cl}^-$ 2. $\text{Mn(VII)} \rightarrow \text{Mn(II)}$ 3. sulfate(IV) $\rightarrow$ sulfate(VI)

May/June 2019

Zinc is obtained from its ore, zinc blende, by means of two chemical reactions. 1 $2\text{ZnS} + 3\text{O}_2 \rightarrow 2\text{ZnO} + 2\text{SO}_2$ 2 $2\text{ZnO} + \text{C} \rightarrow 2\text{Zn} + \text{CO}_2$ In reactions 1 and 2, which substance is reduced?

May/June 2019

Displacement reactions take place between metals and metal ions. They can be used to work out the reactivity order of metals such as lead (Pb), nickel (Ni), and silver (Ag). The ionic equation for a displacement reaction is shown. $\text{Ni(s)} + \text{Pb}^{2+}\text{(aq)} \rightarrow \text{Pb(s)} + \text{Ni}^{2+}\text{(aq)}$ The ionic half-equations for this reaction are shown. $\text{Ni(s)} \rightarrow \text{Ni}^{2+}\text{(aq)} + 2e^-$ $\text{Pb}^{2+}\text{(aq)} + 2e^- \rightarrow \text{Pb(s)}$ These ionic half-equations show nickel atoms donating electrons and lead ions accepting them.

May/June 2019

Copper(II) oxide reacts with iron. The equation for this reaction is shown below. $3\text{CuO} + 2\text{Fe} \rightarrow 3\text{Cu} + \text{Fe}_2\text{O}_3$ Why may this reaction be described as the reduction of copper(II) oxide?

May/June 2021

A redox reaction example is given below. $\text{Zn} + \text{Cu}^{2+} \rightarrow \text{Zn}^{2+} + \text{Cu}$ Which statement correctly describes this reaction?

May/June 2021

A redox reaction example is given. $\text{Zn} + \text{Cu}^{2+} \rightarrow \text{Zn}^{2+} + \text{Cu}$. Which statement about this reaction is correct?

May/June 2021

A redox reaction example is given below. $\text{Zn} + \text{Cu}^{2+} \rightarrow \text{Zn}^{2+} + \text{Cu}$ Which statement about this reaction is correct?

May/June 2021

The formulae for two manganese compounds are $\text{MnO}_2$ and $\text{KMnO}_4$. For both of these compounds, potassium has an oxidation state of $+1$ and oxygen has an oxidation state of $-2$. What are the oxidation states of manganese in each compound?

May/June 2021

In which equation does carbon undergo both oxidation and reduction?

May/June 2022

When aqueous iron(III) chloride, $\text{FeCl}_3$, is mixed with aqueous potassium iodide, $\text{KI}$. $v\text{FeCl}_3 + w\text{KI} \rightarrow x\text{FeCl}_2 + y\text{KCl} + \text{I}_2$ Which of the following statements are correct?

May/June 2022

The transformation of ethanol with acidified potassium manganate(VII) is illustrated. $\text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{KMnO}_4,\ \text{H}^+} \text{CH}_3\text{COOH}$ What type of reaction is occurring?

May/June 2022

Substance J is involved in a redox reaction. During the reaction, J gains electrons. Which statement is correct?

May/June 2022

Metal M reacts with steam and gives off gas G. Which row correctly names gas G and states the type of reaction that takes place when metal M reacts with steam?

May/June 2022

Nitrogen oxide, NO, is produced inside the engine of petrol-powered cars. One component of petrol is octane, $\text{C}_8\text{H}_{18}$. Catalytic converters remove nitrogen oxide from exhaust fumes. Which row shows the reactants that form nitrogen oxide and a reaction that removes it in a catalytic converter?

May/June 2022

Four redox equations, plus statements about them, are presented. Which of these statements about the equations are correct?

May/June 2023

The chemical equation for the reaction of iron(III) oxide with carbon is given below. $2\text{Fe}_2\text{O}_3 + 3\text{C} \rightarrow 4\text{Fe} + 3\text{CO}_2$ What type of reaction does iron(III) oxide undergo?

May/June 2023

Acidified aqueous potassium manganate(VII) forms a purple solution. What does the (VII) in potassium manganate(VII) indicate?

May/June 2023

Sodium ions, $\text{Na}^+$, together with oxygen ions, $\text{O}^{2-}$, join with chromium ions to produce a salt. For sodium dichromate, the formula is $\text{Na}_2\text{Cr}_2\text{O}_7$. What is the oxidation state of chromium in this salt?

May/June 2023

The equation for the reaction between sulfur dioxide and acidified potassium dichromate(VI) is shown: $3\text{SO}_2 + \text{Cr}_2\text{O}_7^{2-} + 2\text{H}^+ \rightarrow 3\text{SO}_4^{2-} + 2\text{Cr}^{3+} + \text{H}_2\text{O}$. Which substance is oxidised, and which species acts as the oxidising agent?

May/June 2023

Which reaction involving hydrochloric acid is a redox reaction?

May/June 2023

Oxides of nitrogen are produced in car engines and then removed by catalytic converters. Which equation shows a reaction taking place in a catalytic converter?

May/June 2023

Which chemical equation represents an oxidation reaction?

May/June 2024

Iron(III) oxide is reduced by carbon monoxide to form iron and carbon dioxide. What balanced equation represents this reaction?

May/June 2024

In which of the reactions is the underlined substance reduced?

May/June 2024

In a blast furnace, iron is obtained when iron(III) oxide reacts with carbon monoxide. The reaction is given below. $\text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2$ Which substance undergoes oxidation, and which substance undergoes reduction in this reaction?

May/June 2024

The chemical equation for magnesium reacting with carbon dioxide is given below. $2\text{Mg} + \text{CO}_2 \rightarrow 2\text{MgO} + \text{C}$ Which of the following statements about this reaction is correct?

May/June 2024

Car engines produce oxides of nitrogen. Inside a catalytic converter, oxides of nitrogen are removed by letting them react with compound X. Which row states the reaction type that the oxides of nitrogen undergo and identifies compound X?

May/June 2024

Which equation shows a redox reaction?

May/June 2024

The reaction equation for aluminium and copper(II) oxide is given below. $2\text{Al} + 3\text{CuO} \rightarrow \text{Al}_2\text{O}_3 + 3\text{Cu}$ Which of the following statements about this equation are correct?

May/June 2024

A redox equation is given below. $\text{H}_2\text{O}_2 + 2\text{KI} + \text{H}_2\text{SO}_4 \rightarrow \text{I}_2 + \text{K}_2\text{SO}_4 + 2\text{H}_2\text{O}$ Potassium iodide is the ..... 1 ..... agent in this reaction because iodide ions ..... 2 ..... electrons. Which words should be used to fill spaces 1 and 2?

May/June 2024

The chemical equation for the reaction of copper(II) oxide with carbon is given below. $2\text{CuO} + \text{C} \rightarrow 2\text{Cu} + \text{CO}_2$ Which statement about this reaction is correct?

May/June 2025

Which of the following reactions are redox reactions?

May/June 2025

Steam combines with carbon to form carbon monoxide and hydrogen. $\text{C(s)} + \text{H}_2\text{O(g)} \rightarrow \text{CO(g)} + \text{H}_2\text{(g)}$ Which substance is reduced in this reaction?

May/June 2025

In which equations does the underlined species act as a reducing agent?

May/June 2025

The reaction equation for iron(II) sulfate with bromine is given as: $6\text{FeSO}_4 + 3\text{Br}_2 \rightarrow 2\text{Fe}_2(\text{SO}_4)_3 + 2\text{FeBr}_3$. Which row correctly names the oxidising agent and the reducing agent?

May/June 2025

This equation shows a redox reaction: $2\text{Al} + \text{Fe}_2\text{O}_3 \rightarrow 2\text{Fe} + \text{Al}_2\text{O}_3$. What is the change in the oxidation number of iron in this reaction?

May/June 2025

Nitrogen monoxide is formed in a car engine when petrol is burnt. The exhaust gases from the car engine are sent through a catalytic converter. Inside the catalytic converter, the nitrogen monoxide, NO, reacts with carbon monoxide, CO, to produce nitrogen and carbon dioxide. Which statement is not correct?

May/June 2025

This question concerns sulfur compounds.

May/June 2025

Tin is produced when tin(II) oxide is heated with carbon. What change does the tin in tin(II) oxide undergo in this reaction?

Oct/Nov 2016

In which reaction does the copper compound undergo reduction?

Oct/Nov 2016

The equations for three reactions are listed below. 1. $\text{CuO} + \text{H}_2 \rightarrow \text{Cu} + \text{H}_2\text{O}$ 2. $\text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2$ 3. $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$ Which statement about these reactions is not correct?

Oct/Nov 2016

Four ionic half-equations are presented below. 1. $\text{Cu}^{2+}\text{(aq)} + 2e^- \rightarrow \text{Cu(s)}$ 2. $2\text{I}^-\text{(aq)} \rightarrow \text{I}_2\text{(aq)} + 2e^-$ 3. $\text{Fe}^{2+}\text{(aq)} \rightarrow \text{Fe}^{3+}\text{(aq)} + e^-$ 4. $\text{Cl}_2\text{(g)} + 2e^- \rightarrow 2\text{Cl}^-\text{(aq)}$ Which statement is correct?

Oct/Nov 2016

Sulfuric acid is produced by the Contact process. The key reaction occurs in the presence of a catalyst. What are the reactants and the catalyst for this reaction?

Oct/Nov 2016

Which change shows an oxidation reaction?

Oct/Nov 2016

The equations for two reactions P and Q are shown below. P: $2\text{NaNO}_2 + \text{O}_2 \rightarrow 2\text{NaNO}_3$ Q: $2\text{HgO} \rightarrow 2\text{Hg} + \text{O}_2$ For which of these reactions does oxidation of the underlined substance take place?

Oct/Nov 2017

The equations for reactions P and Q are shown below. $\text{P}\quad 2\text{NaNO}_2 + \text{O}_2 \rightarrow 2\text{NaNO}_3$ $\text{Q}\quad 2\text{HgO} \rightarrow 2\text{Hg} + \text{O}_2$ For which of these reactions does oxidation of the underlined substance take place?

Oct/Nov 2017

The reaction equations for P and Q are shown below. P: $2\text{NaNO}_2 + \text{O}_2 \rightarrow 2\text{NaNO}_3$ Q: $2\text{HgO} \rightarrow 2\text{Hg} + \text{O}_2$ For which of these reactions does oxidation of the underlined substance take place?

Oct/Nov 2017

Which metal pairing gives the greatest voltage reading in the cells shown?

Oct/Nov 2017

Copper(II) oxide reacts with hydrogen. $\text{CuO} + \text{H}_2 \rightarrow \text{Cu} + \text{H}_2\text{O}$ Which row is the correct one?

Oct/Nov 2017