May/June 2019

The temperature of a sample of an inert gas is raised. How does this affect the number of molecules with the most probable energy and the number of molecules with high energy?

States of matter

Hydrogen iodide gas can undergo reversible decomposition to form iodine vapour and hydrogen. $2\text{HI}(g) \rightleftharpoons \text{I}_2(g) + \text{H}_2(g) \quad \Delta H = +12\,\text{kJ mol}^{-1}$ The equilibrium position for this reaction can be changed by altering the external conditions. Which row correctly states the shift in equilibrium position?

Equilibria

Sulfur dioxide and oxygen react in a reversible reaction. $\text{2SO}_2(g) + \text{O}_2(g) \rightleftharpoons \text{2SO}_3(g)$  $K_c = 280\ \text{mol}^{-1}\text{dm}^3$ at $1000\ \text{K}$. For an equilibrium mixture at $1000\ \text{K}$, the concentration of sulfur trioxide is $6.00\ \text{mol dm}^{-3}$. The concentration of sulfur dioxide is twice that of oxygen. Calculate the sulfur dioxide concentration.

Equilibria

Under room conditions, $1.15\ \text{g}$ of a metallic element requires $300\ \text{cm}^3$ of oxygen to react fully and produce an oxide containing $\text{O}^{2-}$ ions. What might the metallic element be?

Atoms, molecules and stoichiometry

The graph displays the relative melting points of four elements that follow one another in the Periodic Table. Each of these elements has a proton number below $20$. Which one belongs to Group $16$?

The Periodic Table: chemical periodicity

Substance X is added to water. A gas is released and the pH of the resulting solution rises. The solution is then treated with sulfuric acid, producing a white precipitate. What could substance X be?

Group 2

The solutions of $0.1\ \text{mol dm}^{-3}\ \text{Mg(NO}_3)_2$ and $0.1\ \text{mol dm}^{-3}\ \text{Ba(NO}_3)_2$ are each treated separately in a sequence of reactions with pure reagents. M, N and P are magnesium compounds. Q, R and S are barium compounds. How many of M, N, P, Q, R and S are white precipitates?

Equilibria

Concentrated sulfuric acid is introduced to separate solid samples of sodium chloride, sodium bromide and sodium iodide. For which samples does sulfuric acid function as an oxidising agent?

Electrochemistry

If bromine is reacted with warm $\text{NaOH}(aq)$, the products formed have the same oxidation numbers, and in the same proportions, as those formed when chlorine reacts with hot $\text{NaOH}(aq)$. In one reaction between bromine and warm $\text{NaOH}(aq)$, a product containing sodium, bromine and oxygen has a mass of $30.2\ \text{g}$. What mass of $\text{NaOH}$ reacted?

Atoms, molecules and stoichiometry

When the temperature is $550\,^{\circ}\text{C}$, nitrogen dioxide reacts with unburnt hydrocarbon fragments such as $\text{CH}_3$ inside the catalytic converter of a motor vehicle. $\text{4CH}_3 + \text{7NO}_2 \rightarrow 3\tfrac{1}{2}\text{N}_2 + 4\text{CO}_2 + 6\text{H}_2\text{O}$ Which row indicates the energy change for this reaction and a plausible explanation for it?

Chemical energetics

Which of the following statements is correct?

Nitrogen and sulfur

A sample of element X is examined by mass spectrometry. The mass spectrum produced is shown. What is the relative atomic mass of this sample of element X?

Atomic structure

The diagrams illustrate two different compounds. Determine: • the total number of structural isomers, including compound $2$, that could result from adding a second methyl group to the ring of compound $1$? • the number of $\pi$ electrons in each compound?

Chemical bonding

Which compound is represented by the molecular formula $\text{C}_6\text{H}_{10}\text{O}$?

Atoms, molecules and stoichiometry

What is the structural formula of the main product formed when hydrogen bromide reacts with $2$-methylbut-$2$-ene?

Hydrocarbons

Which reaction is most likely to involve the formation of an intermediate carrying a positive charge?

Reaction kinetics

The infra-red spectrum of a substance whose empirical formula is $\text{C}_2\text{H}_4\text{O}$ is displayed. Which bonds cause peak X and peak Y?

Chemical bonding

The structure of coniine is shown here. Coniine may be prepared by allowing ammonia to react with a dibromo compound, X. $\text{NH}_3 + \text{C}_8\text{H}_{16}\text{Br}_2 \rightarrow \text{coniine} + 2\text{HBr}$ State the name of compound X.

Nitrogen compounds

When answering this question, consider both structural isomerism and stereoisomerism. 3-methylhexan-3-ol is heated with concentrated sulfuric acid to produce a number of isomeric compounds having the molecular formula $\text{C}_7\text{H}_{14}$. How many isomeric compounds can be formed in this reaction?

Hydrocarbons

Organic compound T takes part in these reactions. • T is oxidised by hot, acidified potassium manganate(VII). • T reacts with sodium and produces hydrogen. Which compound could T be?

Hydroxy compounds

Compound X is reacted in turn with two reagents, giving compound Z. Initially, X is treated with a mild oxidising agent to yield Y. Y is then reacted with $\text{NaBH}_4$ to give Z. What could Z be?

Carbonyl compounds

Which reagent can be used to tell propanone apart from ethanol?

Carbonyl compounds

A washing powder has sodium hydrogencarbonate, $\text{NaHCO}_3$, among its ingredients. In a titration, complete reaction of a solution containing $1.00\,\text{g}$ of this washing powder needs $7.15\,\text{cm}^3$ of $0.100\,\text{mol dm}^{-3}$ sulfuric acid. Only the sodium hydrogencarbonate in the washing powder reacts with the acid. What is the percentage by mass of sodium hydrogencarbonate in the washing powder?

Atoms, molecules and stoichiometry

Which one of the compounds is chiral?

Chemical bonding

A calcium-48 atom can produce a $2+$ ion. Which of these statements about the ion are correct?

Atomic structure

The four elements, W, X, Y and Z, are shown with the electronic configurations below. W: $2,4$ X: $2,6$ Y: $2,8,2$ Z: $2,8,8,1$ Which formulae are the ones that would have boiling points lower than room temperature?

Chemical bonding

Which of these statements about enthalpy changes are correct?

Chemical energetics

Vanadium and pepsin are both able to act as catalysts. Vanadium is a metal, whereas pepsin is an enzyme. Which of the following statements are true for both vanadium and pepsin?

Reaction kinetics

Which oxides will react with water after being left in cold water for one day?

The Periodic Table: chemical periodicity

A hard-glass test-tube is heated strongly while it contains a mixture of magnesium carbonate and magnesium nitrate. Which gases are produced?

Group 2

Which of the following statements about poly(alkene)s are true?

Polymerisation

Compound Y • reacts with alkaline aqueous iodine to produce a yellow precipitate • causes warm, acidified potassium dichromate(VI) solution to change colour. What might compound Y be?

Hydroxy compounds

Several different reactions can produce carboxylic acids. Which of the statements below are correct?

Carboxylic acids and derivatives

The outer electron in a neon atom is found in a specific orbital. Which row gives the orbital’s relative energy and shape?

Atomic structure

Carboxylic acids react with alcohols to form esters. Carboxylic acid X produces just one ester with molecular formula $\text{C}_5\text{H}_{10}\text{O}_2$. What might X be?

Atoms, molecules and stoichiometry

In which species does a lone pair of electrons occur?

Chemical bonding

If an evacuated tube with a volume of $400\,\text{cm}^3$ is filled with gas at $300\,\text{K}$ and $101\,\text{kPa}$, its mass rises by $0.65\,\text{g}$. Treat the gas as behaving ideally. What could be the identity of the gas?

States of matter

In what conditions will nitrogen act most nearly as an ideal gas?

States of matter

The following two reactions are given together with their enthalpy changes. $2\text{C}(s) + 2\text{H}_2(g) \rightarrow \text{C}_2\text{H}_4(g) \quad \Delta H^\circ = +52.2\,\text{kJ mol}^{-1}$ $\text{C}_2\text{H}_2(g) + \text{H}_2(g) \rightarrow \text{C}_2\text{H}_4(g) \quad \Delta H^\circ = -175.8\,\text{kJ mol}^{-1}$ The information above may be used to determine the enthalpy change for the reaction below. $2\text{C}(s) + \text{H}_2(g) \rightarrow \text{C}_2\text{H}_2(g) \quad \Delta H^\circ = X$ What is the value of $X$?

Chemical energetics

Ethanedioic acid, $\text{HO}_2\text{CCO}_2\text{H}$, may be oxidised using $\text{KMnO}_4$ in dilute sulfuric acid. This reaction forms carbon dioxide, water, potassium sulfate and manganese(II) sulfate as products. During this oxidation, each ethanedioic acid molecule gives up two electrons. The half-equation for this change is shown below. $\text{HO}_2\text{CCO}_2\text{H} \rightarrow 2\text{CO}_2 + 2\text{H}^+ + 2e^-$ When five ethanedioic acid molecules are oxidised by $\text{KMnO}_4$ in dilute sulfuric acid, how many water molecules are formed?

Electrochemistry

The Boltzmann distribution showing the molecular energies in a sample of aqueous hydrogen peroxide at room temperature is displayed. Which diagram represents the Boltzmann distribution of molecular energies for aqueous hydrogen peroxide kept at room temperature after the catalyst, manganese(IV) oxide, has been added?

Reaction kinetics

Ethyl ethanoate undergoes the reaction shown below. $\text{CH}_3\text{CO}_2\text{C}_2\text{H}_5 + \text{H}_2\text{O} \rightleftharpoons \text{C}_2\text{H}_5\text{OH} + \text{CH}_3\text{CO}_2\text{H}$ \quad $K_c = 0.27$ Ethanol and ethanoic acid were combined in equal amounts and left until equilibrium was reached. When equilibrium was established, the concentrations of ethanoic acid and ethanol were each $0.42\,\text{mol dm}^{-3}$. What is the equilibrium concentration of ethyl ethanoate?

Equilibria

Which row gives an example of heterogeneous catalysis?

Reaction kinetics

Element Q is easily oxidised when it is in air. The oxide formed then reacts with water to give a solution with a very low pH. In which part of the Periodic Table could element Q be placed?

The Periodic Table: chemical periodicity

The eight elements from sodium through to argon are all in the same period of the Periodic Table. The equation for the first ionisation energy is given below. $\text{X}(g) \rightarrow \text{X}^+(g) + e^-$ Which one of these eight elements has the electron in this equation taken from a filled orbital?

Atomic structure

Elements D and E are each in Period 3. Element D has the smallest atomic radius in Period 3. Only two elements in Period 3 have a melting point lower than that of element E. When elements D and E react together, they form compound L. Which compound might L be?

The Periodic Table: chemical periodicity

How many of the solutions shown, when each is added to a separate sample of magnesium sulfate solution, give a white precipitate? HCl(aq) \quad NH$_3$(aq) \quad $(\text{NH}_4)_2\text{CO}_3$(aq) \quad $\text{Ba(NO}_3)_2$(aq)

Atoms, molecules and stoichiometry

Z is a white solid that dissolves in water. A portion of Z is heated using a Bunsen burner until no more change is seen. When the residue is mixed by shaking with water, a solution is produced and no solid is left behind. What could Z be?

States of matter

An excess of chlorine was passed through $100\,\text{cm}^3$ of hot $6.0\,\text{mol dm}^{-3}$ sodium hydroxide. What amount, in moles, of sodium chloride would form in the reaction?

Atoms, molecules and stoichiometry

Ammonium sulfate, $(\text{NH}_4)_2\text{SO}_4$, and ammonium nitrate, $\text{NH}_4\text{NO}_3$, are both used as fertilisers. These salts contain different percentages by mass of nitrogen. They have the same effect on the pH of wet neutral soil as each other. Which row is the correct one?

Nitrogen and sulfur

Which reaction produces a product that is an atmospheric pollutant responsible for acid rain?

Nitrogen and sulfur

Oxygen possesses three stable isotopes, $^{16}\text{O}$, $^{17}\text{O}$ and $^{18}\text{O}$. A specimen of oxygen gas, $\text{O}_2$, contains all three isotopes and is examined with a mass spectrometer. How many peaks caused by the $\text{O}_2^+$ ion would be expected?

Atoms, molecules and stoichiometry

3-methylbut-1-ene is capable of taking part in several kinds of reaction. Which row correctly gives the reaction types?

Hydrocarbons

Compound X does not exhibit cis-trans isomerism. What might compound X be?

Chemical bonding

The diagram shows the repeat unit of an addition polymer. What is the correct name of the monomer that would produce this polymer?

Chemical bonding

A molecule of geraniol is shown. What product is obtained when geraniol is reacted with excess cold, dilute, acidified manganate(VII) ions?

Hydroxy compounds

Alcohol W cannot be prepared by reducing a carboxylic acid using LiAlH$_4$. When Alcohol W is dehydrated with concentrated sulfuric acid, it forms only one product. What is a possible identity for W?

Hydroxy compounds

Which product can be formed from bromoethane through an elimination reaction?

Chemical bonding

Propene, bromine and hydrogen bromide are combined in the absence of light. Several products are produced, with some present only in very small amounts. Which substance will be absent from the product mixture?

Hydrocarbons

Which reagent could be used to tell ethanal and propanal apart?

Carbonyl compounds

The diagram indicates that a carboxylic acid P can be made from X, Y or Z. Which row is the correct one?

Carboxylic acids and derivatives

A single molecule of compound R is shown. Identify compound R and state how its boiling point compares with that of butanoic acid?

States of matter

The graphs display the first eight consecutive ionisation energies for two elements from Period 3 of the Periodic Table. What is the formula of the ionic compound produced by these elements?

The Periodic Table: chemical periodicity

The diagram presents the infra-red spectrum of Q. What substance could Q be?

Chemical bonding

If $\text{O}_2$ reacts with $\text{H}_2\text{S}$, the products formed are $\text{SO}_2$ and $\text{H}_2\text{O}$. Mixture Y has an equal count of the two molecules shown, with no additional molecules present. Which statements about Y are correct?

Atoms, molecules and stoichiometry

Which statements regarding an atom of $^{99}\text{Tc}$ are correct?

Atomic structure

In which reactions do the nitrogen atoms undergo reduction?

Nitrogen and sulfur

The production of ammonia from nitrogen and hydrogen is a significant industrial process. Which of the following would keep the equilibrium constant, $K_p$, for ammonia formation unchanged?

Equilibria

Which reactions involving calcium and its compounds result in two gaseous products?

Group 2

A small amount of hot, concentrated sulfuric acid is added separately to solid samples of potassium halides, $\text{KX}$. Which of the potassium halides reacts to form a mixture of products that includes a halogen, $\text{X}_2$?

Group 17

The diagram depicts a compound that is used as a flame retardant. Which of the statements about this structure are correct?

Chemical bonding

Hydrolysis of halogenoalkanes can be carried out with aqueous sodium hydroxide. Which compounds are generally hydrolysed by an $\text{S}_\text{N}1$ mechanism?

Reaction kinetics

In an organic synthesis, the product is obtained in 62% yield. Which of the following conversions fit this information?

Atoms, molecules and stoichiometry

A $\sigma$ bond forms between two carbon atoms in an ethene molecule. Which diagram shows the orbital overlap that happens in forming this bond?

Chemical bonding

An oxidising agent that can turn ethanal into ethanoic acid or ethanoate ions will also oxidise methanoic acid, $\text{HCO}_2\text{H}$, to carbon dioxide and water. Which reagents, when heated, react in different ways with $\text{HCO}_2\text{H}$ and $\text{CH}_3\text{CO}_2\text{H}$?

Electrochemistry

The table compares some properties of four substances. Which substance might be potassium iodide?

Chemical bonding

X, Y and Z are all gases that behave ideally and react according to the equation shown. $\text{X(g)} + 2\text{Y(g)} \rightarrow 2\text{Z(g)}$ If $3.0\,\text{mol}$ of X and $3.0\,\text{mol}$ of Y are put into a container of volume $1.0\,\text{dm}^3$, they react to produce the maximum possible amount of Z. The final temperature of the reaction vessel is $120\,^{\circ}\text{C}$. What pressure is finally present in the reaction vessel?

States of matter

Which two substances are both simple molecules?

Chemical bonding

A reaction pathway diagram is displayed. Which row is the correct one?

Chemical energetics

X may be either chlorine or a chlorine oxide. When X reacts with water, under suitable conditions, it produces the two acids HCl and HClO$_3$ in the mole ratio of $1$ (HCl) : $5$ (HClO$_3$). What might X be?

Electrochemistry

Manganese and nitrogen are able to exhibit a variety of oxidation states. Calculate the total of the oxidation states of Mn and N in each row of the table. In which row is this total the smallest?

Electrochemistry

X and Y combine to make Z in a reversible reaction. At a higher temperature, the equilibrium yield of Z is lower. At a lower pressure, the equilibrium yield of Z is lower. Which equation could show this reaction?

Equilibria

The amount of carbon dioxide gathered when $0.100\,\text{mol}$ of magnesium carbonate reacts with $50.0\,\text{cm}^3$ of $1.00\,\text{mol dm}^{-3}$ sulfuric acid is recorded as time passes. The gas volume is then drawn on a graph against time, producing the line called P. The investigation is carried out again with $0.100\,\text{mol}$ of the same magnesium carbonate, but using another acid sample. All other conditions are kept unchanged. When these readings are plotted, they produce the line called Q. Which acid sample could produce the line called Q?

Reaction kinetics

Sodium and sulfur combine to produce sodium sulfide, $\text{Na}_2\text{S}$. How does the atomic radius and the ionic radius of sodium compare with the corresponding values for sulfur?

The Periodic Table: chemical periodicity

Which graph shows how electronegativity varies across the elements in Period 3?

Chemical bonding

Separate test-tubes each contain solid barium carbonate and solid magnesium carbonate, and dilute hydrochloric acid is then added. Separate test-tubes each contain $0.1\,\text{mol dm}^{-3}$ barium chloride and $0.1\,\text{mol dm}^{-3}$ magnesium chloride, and dilute sodium hydroxide is then added. Which row is the correct one?

Group 2

Water from a river in an agricultural region contains $\text{NH}_4^+$, $\text{CO}_3^{2-}$, $\text{HCO}_3^-$, $\text{Cl}^-$ and $\text{NO}_3^-$ ions. At a water treatment plant, a calculated amount of calcium hydroxide is added to treat this water. Which substance is formed as a precipitate when calcium hydroxide is added to the river water?

Group 2

Solid sodium chloride and solid sodium iodide each react with concentrated sulfuric acid at room temperature. For $\text{NaCl}$, the products formed are $\text{NaHSO}_4$ and $\text{HCl}$. For $\text{NaI}$, the products are $\text{NaHSO}_4$, $\text{HI}$, $\text{I}_2$, $\text{SO}_2$, $\text{H}_2\text{O}$, $\text{S}$ and $\text{H}_2\text{S}$. What explains the difference between these products?

Electrochemistry

A solution in water of a calcium compound is first treated with a mixture of dilute aqueous nitric acid and aqueous silver nitrate. The white precipitate that forms then dissolves after dilute aqueous ammonia is added. What is the relative molecular mass, $M_r$, of the calcium compound?

Analytical techniques

Which statement concerning the ammonium ion is correct?

Chemical bonding

Inside a catalytic converter, $5.6\,\text{g}$ of carbon monoxide reacts with an excess of nitrogen monoxide. What is formed in this reaction?

Atoms, molecules and stoichiometry

A mass spectrum for an alloy made of copper and gold is displayed. Which expression can be used to find the relative atomic mass, $A_r$, of the copper in this sample?

Analytical techniques

The Finkelstein reaction takes place when NaI in propanone is used with either a chloroalkane or a bromoalkane. The halogen atom is replaced directly by I. This reaction functions only with primary halogenoalkanes. Which halogenoalkane gives compound X?

Halogen compounds

The diagram depicts the skeletal formula of compound Y. Determine the empirical formula of Y.

An introduction to AS Level organic chemistry

In polymer Z, each carbon atom along the polymer chain is attached to one hydrogen atom and one methyl group. Which alkene can be polymerised to produce polymer Z?

Chemical bonding

Which compound would, on treatment with hot, concentrated acidified manganate(VII) ions, give a carboxylic acid and a ketone?

Electrochemistry

Water is added to a sample of $2,3$-dibromohexane. Some of the $2,3$-dibromohexane is completely hydrolysed, while the rest is only partially hydrolysed. Which substance is absent from the mixture of products?

Halogen compounds

Which statement about the mechanism of an $\text{S}_\text{N}1$ reaction involving a halogenoalkane is correct?

Reaction kinetics

When answering this question, take account of structural isomerism and stereoisomerism. Which isomer of $\text{C}_6\text{H}_{13}\text{OH}$ produces the largest number of distinct alkenes on dehydration?

Hydroxy compounds

When compound Q is treated with $2,4$-dinitrophenylhydrazine, a precipitate forms. Compound Q does not form a precipitate on warming with Fehling’s solution. What might compound Q be?

Carbonyl compounds

Only structural isomerism is to be taken into account for this question. A collection of isomeric compounds, each with molecular formula $\text{C}_5\text{H}_{10}\text{O}$, all undergo nucleophilic addition with excess HCN in a $1:1$ ratio. How many isomeric compounds are there in the collection?

Carbonyl compounds

Which two substances could react to produce the ester $\text{CH}_3\text{CH}_2\text{CO}_2\text{CH}_3$?

Carboxylic acids and derivatives

Which atom contains exactly three unpaired electrons?

Atomic structure

An ester is shown. What structure would the carboxylic acid have that is produced when the ester linkage undergoes acid hydrolysis?

Carboxylic acids and derivatives

Which statements about the $^{209}_{83} \text{Bi}$ atom are correct?

Atomic structure

When looking at the two common isotopes of chlorine, which statements are correct?

Atomic structure

Which enthalpy changes always have a negative value of $\Delta H$?

Chemical energetics

The diagram illustrates the Boltzmann distribution of molecular energies for one mole of a gas at two temperatures, $T_1$ and $T_2$. Which statements are correct?

Reaction kinetics

Which of the following statements about sodium chloride are correct?

Chemical bonding

Which gases dissolve in water and make the pH lower?

Equilibria

Which compounds possess optical isomers?

Chemical bonding

Bromine undergoes addition with ethene. Which of the following statements about this reaction are correct?

Chemical bonding

An unidentified organic compound $Z$ reacts with sodium to produce a flammable gas as one product. $Z$ does not form a yellow precipitate with alkaline aqueous iodine. Which of the following could be the identity of $Z$?

Hydroxy compounds

W is an element in period three of the Periodic Table, and it forms a white solid oxide, X. X is thermally stable, has a very high melting point, and dissolves slightly in water. Which row identifies the structure and bonding of X?

Chemical bonding

An organic molecule $X$ has the molecular formula $\text{C}_5\text{H}_{10}\text{O}_2$. Its infra-red spectrum shows a strong peak at $1250\,\text{cm}^{-1}$, another strong peak at $1720\,\text{cm}^{-1}$, but no strong peak above $3100\,\text{cm}^{-1}$. Which one of the following compounds could $X$ be?

Carboxylic acids and derivatives

Ethane, $\text{CH}_3\text{CH}_3$, and fluoromethane, $\text{CH}_3\text{F}$, contain the same total number of electrons in their molecules. Their boiling points are listed as follows: $\text{CH}_3\text{CH}_3$ = $184.5\,\text{K}$, $\text{CH}_3\text{F}$ = $194.7\,\text{K}$. What causes this difference in boiling points?

States of matter

A reaction pathway diagram for a chemical reaction is shown. Which statement is correct?

Chemical energetics

Which changes in conditions or molecular properties make gases more likely to behave in an ideal way?

States of matter

Dilute acidified dichromate(VI) ions can oxidise ethanol to ethanal. The oxidation reaction equation is $\text{C}_2\text{H}_5\text{OH} \rightarrow \text{C}_2\text{H}_4\text{O} + 2\text{H}^+ + 2e^-.$ The reduction reaction equation is $\text{Cr}_2\text{O}_7^{2-} + 14\text{H}^+ + 6e^- \rightarrow 2\text{Cr}^{3+} + 7\text{H}_2\text{O}.$ Which of these equations is correct?

Electrochemistry

Which is the correct expression for $K_c$ for the reaction shown? $\text{I}_2(aq) + 2\text{Fe}^{2+}(aq) \rightleftharpoons 2\text{I}^-(aq) + 2\text{Fe}^{3+}(aq)$

Equilibria