Electrochemistry

Sodium chloride and sodium iodide are reacted with concentrated sulfuric acid. Which of these statements are correct?

Feb/March 2017

Which reaction is not a redox reaction?

Feb/March 2018

Bromine is obtained from sea-water. During the last part of the process, two redox reactions occur. $\text{Br}_2$(aq) $+\ \text{SO}_2$(g) $+\ \text{2H}_2\text{O}$(l) $\rightarrow\ \text{2HBr}$(aq) $+\ \text{H}_2\text{SO}_4$(aq) $\text{2HBr}$(aq) $+\ \text{Cl}_2$(g) $\rightarrow\ \text{Br}_2$(g) $+\ \text{2HCl}$(aq) Which row is the correct one?

Feb/March 2018

Chlorine reacts with hot aqueous sodium hydroxide. Which oxidation states are shown by chlorine in the products formed in this reaction?

Feb/March 2018

In acidic solution, potassium manganate(VII) is reacted with iron(II) ethanedioate, $\text{FeC}_2\text{O}_4$. The half-equations involved are shown below. $\text{MnO}_4^- + 8\text{H}^+ + 5\text{e}^- \rightarrow \text{Mn}^{2+} + 4\text{H}_2\text{O}$ $\text{Fe}^{2+} \rightarrow \text{Fe}^{3+} + \text{e}^-$ $\text{C}_2\text{O}_4^{2-} \rightarrow 2\text{CO}_2 + 2\text{e}^-$ How many moles of iron(II) ethanedioate are required to react with 1 mole of potassium manganate(VII)?

Feb/March 2019

What product is obtained if 3-methylpentane-1,3,4-triol is heated under reflux in the presence of excess acidified potassium dichromate(VI)?

Feb/March 2019

On heating compound X with $\text{Cr}_2\text{O}_7^{2-}/\text{H}^+$, the solution changes from orange to green. The organic product from this reaction is then tested in two ways. Tollens’ reagent: no visible change 2,4-dinitrophenylhydrazine: orange precipitate forms What could compound X be?

Feb/March 2019

In which of these reactions is the underlined substance reduced?

Feb/March 2019

After the equation has been balanced correctly, what is the value of $c$? $a\text{C}_2\text{H}_4 + b\text{H}_2\text{O} + c\text{H}^+ + 2\text{MnO}_4^- \rightarrow d\text{C}_2\text{H}_6\text{O}_2 + e\text{Mn}^{2+}$

Feb/March 2020

Aqueous sodium hydroxide, when heated, reacts with chlorine. $6\text{NaOH(aq)} + 3\text{Cl}_2(g) \rightarrow 5\text{NaCl(aq)} + \text{NaClO}_3(aq) + 3\text{H}_2\text{O(l)}$ Which statement is correct?

Feb/March 2020

For the redox equation below, in what way do the oxidation states of vanadium and sulfur alter? $\text{VO}_2^+ + \text{SO}_2 \rightarrow \text{V}^{3+} + \text{SO}_4^{2-}$

Feb/March 2020

Chlorine gas is treated with aqueous sodium hydroxide. The oxidation number of chlorine changes from $0$ to $-1$ and also from $0$ to $+1$. At what conditions does this reaction take place, and what is the colour of the solid silver salt containing chlorine in oxidation state $-1$?

Feb/March 2021

When concentrated sulfuric acid reacts with sodium iodide, the products formed include sulfur, iodine, hydrogen sulfide and sulfur dioxide. Which statement is correct in this case?

Feb/March 2021

$\text{NO}$, $\text{NO}_2$, $\text{CO}$ and unburnt hydrocarbons are found in the exhaust gases of internal combustion engines. If catalytic converters are fitted to remove these substances from the exhaust gases, redox reactions take place. What occurs to each compound inside the catalytic converter?

Feb/March 2021

Which compound, when refluxed with an acidified solution of potassium dichromate(VI), gives a ketone?

Feb/March 2021

$\text{VO}_2\text{Cl}$ reacts with NaI in acidic conditions. $2\text{VO}_2\text{Cl} + 2\text{H}_2\text{SO}_4 + 2\text{NaI} \rightarrow \text{VOCl}_2 + \text{VOSO}_4 + \text{I}_2 + \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O}$ The oxidation state of Cl is $-1$ in $\text{VO}_2\text{Cl}$ and in $\text{VOCl}_2$. Which row describing this reaction is correct?

Feb/March 2021

The two half-equations are given below. $\text{MnO}_4^- + 2\text{H}_2\text{O} + 3e^- \rightarrow \text{MnO}_2 + 4\text{OH}^-$ $2\text{OH}^- + \text{SO}_3^{2-} \rightarrow \text{SO}_4^{2-} + \text{H}_2\text{O} + 2e^-$ The balanced equation for the reaction of manganate(VII) ions with sulfite ions is written as $u\text{MnO}_4^- + v\text{H}_2\text{O} + w\text{SO}_3^{2-} \rightarrow x\text{MnO}_2 + y\text{SO}_4^{2-} + z\text{OH}^-$ Which of the statements below are correct?

Feb/March 2022

Four equations showing reactions of nitrogen or a compound of nitrogen are given. Which equation shows a disproportionation reaction?

Feb/March 2023

If illudin S is warmed under reflux with excess acidified potassium dichromate(VI), compound M is produced. What molecular formula does compound M have?

Feb/March 2023

Silicon reacts with a blend of calcium oxide and magnesium oxide at $1200\,^\circ\text{C}$. $2\text{MgO} + 2\text{CaO} + \text{Si} \rightarrow 2\text{Mg} + \text{Ca}_2\text{SiO}_4$ Which statement concerning this reaction is correct?

Feb/March 2023

The equation below represents one reaction in a rechargeable lead/acid battery. $\text{Pb}(s) + \text{PbO}_2(s) + 4\text{H}^+(aq) + 2\text{SO}_4^{2-}(aq) \rightarrow 2\text{PbSO}_4(s) + 2\text{H}_2\text{O}(l)$. Which statement concerning this reaction is correct?

Feb/March 2024

$\text{KMnO}_4$ acts as an oxidising agent. Its reaction with $\text{Fe}^{2+}$ is represented by the ionic equation below. $\ldots X\ldots \text{MnO}_4^- + \ldots \text{Fe}^{2+} + \ldots \text{H}^+ \rightarrow \ldots \text{Mn}^{2+} + \ldots Y\ldots \text{Fe}^{3+} + \ldots \text{H}_2\text{O}$ When the equation is balanced, what are $X$ and $Y$?

Feb/March 2024

Three reaction equations involving chlorine or chlorine compounds are given below. 1. $2\text{KClO}_3 \rightarrow 2\text{KCl} + 3\text{O}_2$ 2. $4\text{KClO}_3 \rightarrow 3\text{KClO}_4 + \text{KCl}$ 3. $6\text{KOH} + 3\text{Cl}_2 \rightarrow 3\text{H}_2\text{O} + 5\text{KCl} + \text{KClO}_3$ Which statement is correct for these equations?

Feb/March 2024

Hydroxyethanal, $\text{HOCH}_2\text{CHO}$, is heated under reflux in excess acidified $\text{K}_2\text{Cr}_2\text{O}_7$ until oxidation can no longer occur. Which skeletal formula represents the organic product?

Feb/March 2024

Copper undergoes reaction with nitric acid in certain conditions. The products formed are copper(II) nitrate, water and a nitrogen oxide. $3$ mol of copper reacts with exactly $8$ mol of nitric acid. What is the oxidation state of nitrogen in the oxide formed?

Feb/March 2025

U, V and W are three different halogens. The table summarises nine experiments in which aqueous $\text{U}_2$, $\text{V}_2$ and $\text{W}_2$ were each added separately to aqueous solutions containing $\text{U}^-$, $\text{V}^-$ and $\text{W}^-$ ions. (Results summary) $\text{U}_2(aq)$ does not react with $\text{U}^-(aq)$, $\text{V}^-(aq)$ or $\text{W}^-(aq)$. $\text{V}_2(aq)$ produces $\text{U}_2$ with $\text{U}^-(aq)$, does not react with $\text{V}^-(aq)$, and produces $\text{W}_2$ with $\text{W}^-(aq)$. $\text{W}_2(aq)$ produces $\text{U}_2$ with $\text{U}^-(aq)$ and does not react with $\text{V}^-(aq)$ or $\text{W}^-(aq)$. Which row gives the ions $\text{U}^-$, $\text{V}^-$ and $\text{W}^-$ in descending order of reducing strength?

Feb/March 2025

Which of the following reactions are redox reactions?

May/June 2010

Sulfur dioxide and sulfites are added as food preservatives. What is the reason for using them in this way?

May/June 2010

When heated, ammonium nitrate, $\text{NH}_4\text{NO}_3$, may break down explosively. $\text{NH}_4\text{NO}_3 \rightarrow \text{N}_2\text{O} + 2\text{H}_2\text{O}$ How do the oxidation numbers of the two nitrogen atoms in $\text{NH}_4\text{NO}_3$ change as this reaction occurs?

May/June 2010

Which of these reactions count as redox reactions?

May/June 2010

Ammonium nitrate, $\text{NH}_4\text{NO}_3$, may break down explosively if heated. $\text{NH}_4\text{NO}_3 \rightarrow \text{N}_2\text{O} + 2\text{H}_2\text{O}$ How do the oxidation numbers of the two nitrogen atoms in $\text{NH}_4\text{NO}_3$ change as this reaction occurs?

May/June 2010

Which of the following reactions are redox reactions?

May/June 2010

Sulfur dioxide and sulfites are used in food preservation. What is the reason for using them for this purpose?

May/June 2010

Ammonium nitrate, $\text{NH}_4\text{NO}_3$, may undergo explosive decomposition on heating. $\text{NH}_4\text{NO}_3 \rightarrow \text{N}_2\text{O} + 2\text{H}_2\text{O}$ How do the oxidation numbers of the two nitrogen atoms in $\text{NH}_4\text{NO}_3$ change as this reaction occurs?

May/June 2010

X, Y and Z are three different halogens. The table presents the outcomes of nine experiments in which aqueous solutions of $\text{X}_2$, $\text{Y}_2$ and $\text{Z}_2$ were each added separately to aqueous solutions containing $\text{X}^-$, $\text{Y}^-$ and $\text{Z}^-$. Which row in the table below lists the ions $\text{X}^-$, $\text{Y}^-$ and $\text{Z}^-$ in descending order of reducing agent strength?

May/June 2011

A student noted the outcomes when sodium chloride and sodium iodide were each reacted separately with concentrated sulfuric acid and with concentrated phosphoric acid. The results are shown in the table. Which deduction can be made from these observations?

May/June 2011

In waterlogged soils, such as those used for rice growing, the oxygen level is low. In these soils, anaerobic bacteria lead to nitrogen being lost from the soil, as represented by the sequence below. $\text{NO}_3^-\text{(aq)} \xrightarrow{A} \text{NO}_2^-\text{(aq)} \xrightarrow{B} \text{NO(g)} \xrightarrow{C} \text{N}_2\text{O(g)} \xrightarrow{D} \text{N}_2\text{(g)}$ In which step does the change in oxidation number (oxidation state) of nitrogen differ from the changes in the other steps?

May/June 2011

In the extraction of aluminium by electrolysis of molten aluminium oxide, what is the purpose of adding cryolite to the aluminium oxide?

May/June 2011

Concentrated sulfuric acid may act both as a strong acid and as an oxidising agent. For which compound does concentrated sulfuric acid react in this manner?

May/June 2011

In which compound do two different elements have the same oxidation state?

May/June 2011

Aluminium is the most plentiful metal in the Earth’s crust. Aluminium is obtained by electrolysing aluminium oxide dissolved in molten cryolite. What material is used to make each electrode in this electrolysis?

May/June 2011

If the yellow liquid $\text{NCl}_3(l)$ is added to aqueous sodium hydroxide and stirred, the reaction that takes place can be shown by the following equation. $2\text{NCl}_3(l) + 6\text{NaOH}(aq) \rightarrow \text{N}_2(g) + 3\text{NaCl}(aq) + 3\text{NaOCl}(aq) + 3\text{H}_2\text{O}(l)$ What outcome will this reaction produce?

May/June 2011

X, Y and Z are three different halogens. The table presents the outcomes of nine experiments in which aqueous solutions of $\text{X}_2$, $\text{Y}_2$ and $\text{Z}_2$ were added separately to separate aqueous solutions containing $\text{X}^-$, $\text{Y}^-$ and $\text{Z}^-$ ions. Which row in the table below lists the ions $\text{X}^-$, $\text{Y}^-$ and $\text{Z}^-$ in descending order of their reducing power?

May/June 2011

During the extraction of aluminium by electrolysis of molten aluminium oxide, why is cryolite mixed with the aluminium oxide?

May/June 2011

Sorbitol is an artificial sweetener that is used to make chocolate sweet and is suitable for diabetics. Which functional groups may be formed when this molecule undergoes oxidation under appropriate conditions?

May/June 2011

In waterlogged soils, such as those used for rice growing, the oxygen level is low. In these conditions, anaerobic bacteria remove nitrogen from the soil, as represented by the sequence below. $\text{NO}_3^-(aq) \xrightarrow{A} \text{NO}_2^-(aq) \xrightarrow{B} \text{NO}(g) \xrightarrow{C} \text{N}_2\text{O}(g) \xrightarrow{D} \text{N}_2(g)$ At which step does the change in oxidation number (oxidation state) of nitrogen differ from the changes in the other steps?

May/June 2011

Titanium oxide, $\text{TiO}_2$, is used as a ‘whitener’ in toothpaste. It is produced from the ore iron(II) titanate, $\text{FeTiO}_3$. What change, if any, occurs in the oxidation number (oxidation state) of titanium during the reaction $\text{FeTiO}_3 \rightarrow \text{TiO}_2$?

May/June 2012

The diagram illustrates a cell used in the production of aluminium. Which statement is not correct?

May/June 2012

During the treatment of domestic water supplies, chlorine is introduced into the water to produce $\text{HClO}$. $\text{Cl}_2(\text{aq}) + \text{H}_2\text{O(l)} \rightarrow \text{H}^+(\text{aq}) + \text{Cl}^-(\text{aq}) + \text{HClO(aq)}$ The $\text{HClO}$ then reacts further, forming $\text{ClO}^-$ ions. $\text{HClO(aq)} + \text{H}_2\text{O(l)} \rightarrow \text{H}_3\text{O}^+(\text{aq}) + \text{ClO}^-(\text{aq})$ Both $\text{HClO}$ and $\text{ClO}^-$ destroy bacteria through oxidation. What is the overall change in oxidation number of chlorine when the $\text{ClO}^-$ ion is formed from aqueous chlorine?

May/June 2012

In which substance is nitrogen found at its highest oxidation state?

May/June 2012

Titanium oxide, $\text{TiO}_2$, is used as a ‘whitener’ in toothpaste. It is made from the ore iron(II) titanate, $\text{FeTiO}_3$. What, if any, change takes place in the oxidation number (oxidation state) of titanium in the reaction $\text{FeTiO}_3 \rightarrow \text{TiO}_2$?

May/June 2012

During the disinfection of domestic water supplies, chlorine is introduced into the water to produce HClO. $\text{Cl}_2(aq) + \text{H}_2\text{O}(l) \rightarrow \text{H}^+(aq) + \text{Cl}^-(aq) + \text{HClO}(aq)$ The HClO then goes on to form $\text{ClO}^-$ ions. $\text{HClO}(aq) + \text{H}_2\text{O}(l) \rightarrow \text{H}_3\text{O}^+(aq) + \text{ClO}^-(aq)$ Both HClO and $\text{ClO}^-$ destroy bacteria through oxidation. What is the net change in oxidation number of chlorine when the $\text{ClO}^-$ ion is formed from aqueous chlorine?

May/June 2012

The compounds below are identified as W, X, Y and Z: $\text{W: CH}_3\text{COCH}_2\text{CH}_2\text{OH}$ $\text{X: CH}_3\text{COCH}_2\text{CHO}$ $\text{Y: CH}_3\text{CH(OH)CH}_2\text{CH}_3$ $\text{Z: CH}_3\text{CH}_2\text{CH}_2\text{CHO}$ Which one or more of these compounds may be oxidised by acidified dichromate(VI) solution and also gives a positive result with Tollens’ reagent?

May/June 2012

The diagram depicts a cell used for the production of aluminium. Which statement is not correct?

May/June 2012

Solutions that contain chlorate(I) ions are used as household bleach agents and disinfectants. On heating, these solutions decompose as shown. $3\text{ClO}^- \rightarrow \text{ClO}_3^- + 2\text{Cl}^-$ What oxidation state does chlorine have in each of these three ions?

May/June 2013

A solution containing $ ext{Sn}^{2+}$ ions can reduce an acidified solution of $ ext{MnO}_4^-$ ions to form $ ext{Mn}^{2+}$ ions. In this process, the $ ext{Sn}^{2+}$ ions are oxidised into $ ext{Sn}^{4+}$ ions. How many moles of $ ext{Mn}^{2+}$ ions are produced when a solution made from $9.5\,\text{g}$ of $ ext{SnCl}_2$ ($M_r = 190$) is added to excess acidified $ ext{KMnO}_4$ solution?

May/June 2013

What occurs when iodine solution is added to a sodium bromide solution?

May/June 2013

Element $85$, astatine, belongs to Group VII. Concentrated sulfuric acid is added to sodium astatide. A mixture of products is formed, containing astatine, hydrogen astatide, hydrogen sulfide, and sodium sulfate. Which product is produced by the oxidation of one of the ions in sodium astatide?

May/June 2013

The diagram illustrates an electrolytic cell used to extract aluminium. Which statement is correct?

May/June 2013

In which reactions does the reagent oxidise the organic compound?

May/June 2013

In the electrolysis of molten aluminium oxide for the production of aluminium with carbon electrodes, two reactions take place one after the other at the anode, and each one gives a different gas. What happens to the oxidation number of oxygen in these reactions?

May/June 2013

What occurs when bromine solution is added to a solution of sodium iodide?

May/June 2013

How many of the compounds listed below give a carboxylic acid when heated under reflux with hot acidified $\text{K}_2\text{Cr}_2\text{O}_7$? $\text{CH}_3\text{CH}_2\text{CHO}$ $\text{CH}_3\text{COCH}_3$ $\text{CH}_3\text{CH}_2\text{CH}_2\text{OH}$ $\text{CH}_3\text{CHOHCH}_3$

May/June 2013

Which substance is formed when an aqueous solution of butan-2-ol undergoes oxidation under suitable conditions?

May/June 2013

For the redox equation below, what happens to the oxidation states of vanadium and sulfur? $\text{VO}_2^{+} + \text{SO}_2 \rightarrow \text{V}^{3+} + \text{SO}_4^{2-}$

May/June 2013

The upward thrust of a space shuttle was produced by the following reaction between aluminium and ammonium perchlorate. $10\text{Al} + 6\text{NH}_4\text{ClO}_4 \rightarrow 4\text{Al}_2\text{O}_3 + 2\text{AlCl}_3 + 12\text{H}_2\text{O} + 3\text{N}_2$ Which of the statements about this reaction are correct?

May/June 2013

J is a solid element. It is present as an impurity in fossil fuels. Its oxide K is produced in car engines. In the atmosphere, K can be oxidised further to L. Which of the following statements about J, K and L are correct?

May/June 2013

Hydroxyethanal, $\text{HOCH}_2\text{CHO}$, is warmed under reflux with excess acidified potassium dichromate(VI) until oxidation no longer occurs. What is the skeletal formula of the organic product?

May/June 2014

Which pair of reagents would undergo a redox reaction?

May/June 2014

When solid sodium iodide is treated with concentrated sulfuric acid, the products formed are NaHSO$_4$, H$_2$S, SO$_2$ and S. During the formation of which product does sulfur’s oxidation state change by 8?

May/June 2014

Under suitable conditions, which reagent pairs undergo a redox reaction?

May/June 2014

In which reaction does the species shown in bold act as an oxidising agent?

May/June 2014

Which statements explain why sulfur dioxide is used as a food preservative?

May/June 2014

Electrolysing brine in a diaphragm cell is an important industrial process. What occurs at the anode?

May/June 2014

During the industrial electrolysis of brine to produce chlorine, the diaphragm is a porous screen that lets electrolytes pass through while keeping other chemicals apart. Which substance has to be kept separate from the chlorine by the diaphragm?

May/June 2015

Aluminium is produced from aluminium oxide using electrolysis. Which statements are correct?

May/June 2015

Within oxygen difluoride, $\text{OF}_2$, fluorine has an oxidation number of $-1$. $\text{OF}_2$ reacts with sulfur dioxide in accordance with the equation below. $\text{OF}_2 + \text{SO}_2 \rightarrow \text{SO}_3 + \text{F}_2$ What is oxidised and what is reduced in this reaction?

May/June 2015

The diagram illustrates a diaphragm cell used to carry out the electrolysis of brine. Brine is concentrated aqueous sodium chloride. A solution of sodium chlorate(I), which is widely used as bleach, can be prepared by mixing which two substances?

May/June 2015

Chlorate(V) ions, $\text{ClO}_3^-$, form in the redox reaction of chlorine with hot aqueous sodium hydroxide. Oxidation numbers may be used to help balance this reaction equation. What are the coefficients $v$, $x$ and $y$ in the balanced equation? $v\text{Cl}_2(g) + w\text{OH}^-(aq) \rightarrow x\text{Cl}^-(aq) + y\text{ClO}_3^-(aq) + z\text{H}_2\text{O}(l)$

May/June 2015

Which reactions in this list are redox reactions?

May/June 2015

In industry, copper metal is purified using electrolysis. What happens to the masses of the electrodes, and how does the colour of the electrolyte change during this process?

May/June 2015

Barium has a greater reactivity than aluminium. Which extraction process would be appropriate for barium?

May/June 2015

On adding dilute acid to an aqueous solution that contains nitrite ions, $\text{NO}_2^-(aq)$, a mixture of gases is formed. $2\text{H}^+(aq) + 2\text{NO}_2^-(aq) \rightarrow \text{H}_2\text{O}(l) + \text{NO}(g) + \text{NO}_2(g)$ Which statements correctly describe the process?

May/June 2015

Which pairs of reagents would react together in a redox reaction?

May/June 2015

In which reaction does an element undergo the greatest change in oxidation number?

May/June 2015

Brine is a concentrated aqueous solution of sodium chloride. Brine is electrolysed in a diaphragm cell. What is the purpose of the diaphragm?

May/June 2015

Which two reagents would undergo a redox reaction?

May/June 2016

Bromine is in equilibrium with water. $\text{Br}_2 + \text{H}_2\text{O} \rightleftharpoons \text{HOBr} + \text{HBr}$. Which oxidation states of bromine occur in the equilibrium mixture?

May/June 2016

Nitrogen(II) oxide, $\text{NO}$, nitrogen(IV) oxide, $\text{NO}_2$, carbon monoxide, $\text{CO}$, and unburnt hydrocarbons are found in the exhaust gases of internal combustion engines. When catalytic converters are used to remove these compounds from the exhaust gases, redox reactions take place. What change does each compound undergo in the catalytic converter?

May/June 2016

In which reaction is the organic compound oxidized?

May/June 2016

In the treatment of domestic water supplies, chlorine is introduced into the water so that $\text{HClO}$ is formed. $\text{Cl}_2(aq) + \text{H}_2\text{O}(l) \rightarrow \text{H}^+(aq) + \text{Cl}^-(aq) + \text{HClO}(aq)$. The $\text{HClO}$ then reacts further to produce $\text{ClO}^-$ ions. $\text{HClO}(aq) + \text{H}_2\text{O}(l) \rightleftharpoons \text{H}_3\text{O}^+(aq) + \text{ClO}^-(aq)$. Both $\text{HClO}$ and $\text{ClO}^-$ destroy bacteria by oxidation. By how much does the oxidation number of chlorine change when the $\text{ClO}^-$ ion is formed from aqueous chlorine?

May/June 2016

In a set of nine experiments used to compare the reactivity of the halogens, an aqueous solution of each halogen was mixed with an equal volume of an aqueous solution containing halide ions, as set out in the table below. The nine mixtures were then shaken with hexane. After that, the nine tubes were corked and left standing so that the aqueous and organic solvents could separate into layers. In how many test-tubes did a purple upper layer appear?

May/June 2016

Retinol is present in Vitamin A. In suitable conditions, acidified $\text{KMnO}_4$(aq) may be used to cleave C=C bonds. Once these bonds have been cleaved, the fragments may undergo further oxidation. Under what conditions is acidified $\text{KMnO}_4$(aq) used, and what are the final oxidation products said to include?

May/June 2016

On heating $ ext{KClO}_3$, this reaction takes place: $4 ext{KClO}_3 ightarrow 3 ext{KClO}_4 + ext{KCl}$. Which of the statements below are correct?

May/June 2016

If concentrated sulfuric acid is allowed to react with sodium iodide, the products formed include sulfur, iodine, hydrogen sulfide and sulfur dioxide. Which statement is correct?

May/June 2017

Redox reactions occur frequently in Group 17 chemistry. Which statement is correct?

May/June 2017

Household bleaches and disinfectants often contain solutions with chlorate(I) ions. When these solutions are heated, they decompose as shown: $3\text{ClO}^- \rightarrow \text{ClO}_3^- + 2\text{Cl}^-$. Which oxidation state is shown by chlorine in each of these three ions?

May/June 2017

When $\text{K}_2\text{MnO}_4$ is added to water, this reaction takes place: $a\,\text{MnO}_4^{2-}(aq) + b\,\text{H}_2\text{O}(l) \rightarrow c\,\text{MnO}_4^{-}(aq) + d\,\text{MnO}_2(s) + e\,\text{OH}^-(aq)$. What are the values of $a$ and $c$ in the balanced chemical equation?

May/June 2017

When element X is treated with cold, dilute, aqueous sodium hydroxide, two distinct chlorine-containing products, Y and Z, are produced. What are the oxidation states of chlorine in Y and Z?

May/June 2017

A reaction pathway is illustrated. $\text{SO}_2 \xrightarrow{1} \text{SO}_3 \xrightarrow{2} \text{H}_2\text{SO}_4 \xrightarrow{3} \text{H}_2\text{S} \xrightarrow{4} \text{SO}_2$ At each step in this pathway, sulfur is oxidised, reduced, or neither oxidised nor reduced. Which row is correct?

May/June 2017