May/June 2020

Ethene may be oxidised to produce epoxyethane, $\text{C}_2\text{H}_4\text{O}$. $\text{C}_2\text{H}_4(g) + \tfrac{1}{2}\text{O}_2(g) \rightleftharpoons \text{C}_2\text{H}_4\text{O}(g) \quad \Delta H^{\circ} = -107\,\text{kJ mol}^{-1}$ Which combination of conditions results in the highest equilibrium yield of epoxyethane?

Equilibria

For which pair does every species have the same number of unpaired electrons?

Atomic structure

When a sample of solid ammonium chloride is heated, it breaks down. solid ammonium chloride $\rightarrow$ ammonia gas $+$ hydrogen chloride gas In total, $2.4 \times 10^{21}$ molecules of gas are produced. How many hydrogen atoms are there in the gaseous products?

Atoms, molecules and stoichiometry

A white solid consists of a mixture of sodium chloride and sodium iodide. It is dissolved in water in a test-tube. Excess aqueous silver nitrate is then added to the test-tube. A precipitate, X, is formed. Next, excess concentrated ammonia is added to the test-tube that contains X. Once the test-tube has been shaken, a precipitate, Y, is formed. Which statement about X or Y is correct?

Analytical techniques

$6.90\,\text{g}$ of an ammonium salt is heated with excess aqueous sodium hydroxide. The volume of ammonia given off, measured under room conditions, is $2.51\,\text{dm}^3$. Which ammonium salt has been used?

Atoms, molecules and stoichiometry

An excess of MgO is mixed by shaking with water. The mixture produced is then filtered into test-tube P. An excess of BaO is mixed by shaking with water. The mixture produced is then filtered into test-tube Q. Which oxide reacts more quickly with water, and which filtrate has the lower pH?

Group 2

Z is an element with a giant structure. When the chloride of Z reacts with water, it produces a solution with a pH below $5$. Which pair identifies two elements that could be Z?

The Periodic Table: chemical periodicity

Sodium, aluminium and silicon are three elements in Period 3. Each of these elements forms an oxide. Which row shows three correct properties of these oxides?

The Periodic Table: chemical periodicity

$0.25\,\text{g}$ of anhydrous magnesium nitrate is heated strongly until it has fully decomposed. What total volume of gas is formed, measured under room conditions?

Atoms, molecules and stoichiometry

Astatine, At, is positioned beneath iodine in Group $17$ of the Periodic Table. Which statement is most likely to be true?

Group 17

What is the sequence of increasing melting point for the three chlorides shown? $\text{CCl}_4$, $\text{MgCl}_2$, $\text{PCl}_5$

Chemical bonding

Cobalt is able to form the cation $\text{Co(NH}_3)_4\text{Cl}_2^{+}$. What oxidation number does cobalt have in this ion?

Electrochemistry

The skeletal formula for compound X appears below. Which row is the correct one?

An introduction to AS Level organic chemistry

Which of the following statements is correct?

Atoms, molecules and stoichiometry

But-1-ene and but-2-ene are examined separately using cold, dilute acidified manganate(VII) ions. The four students, W, X, Y and Z, each make statements about these alkenes and the diols produced from them.

Electrochemistry

2-bromo-2-methylpentane is a tertiary halogenoalkane. Which organic products are produced when 2-bromo-2-methylpentane is reacted with a hot concentrated ethanolic solution of sodium hydroxide?

Halogen compounds

Poly(propene) is classed as an addition polymer. What are the $\text{C-C-C}$ bond angles in its polymer chain?

Chemical bonding

One alcohol has the molecular formula $\text{C}_5\text{H}_{12}\text{O}$. It exists in several isomeric forms. Which isomer gives a yellow precipitate with alkaline aqueous iodine?

Hydroxy compounds

If compound X is heated under reflux with aqueous sodium hydroxide solution, the products obtained are sodium ethanoate and hexan-1-ol. Which compound is X?

Carboxylic acids and derivatives

What is the principal product Z formed in the reaction shown below? The compound given reacts with an excess of dry HBr when warmed, producing Z.

Halogen compounds

The structural formula of compound Q is given below. What is the number of chiral centres in one molecule of Q?

Chemical bonding

The infra-red spectrum of compound X is shown below. What might compound X be?

Analytical techniques

For a single molecule of ethene, which row gives both the hybridisation of the carbon atoms’ atomic orbitals and the type of bonding present overall?

Chemical bonding

Which reaction results in an organic anion with a high yield?

Organic synthesis

The meanings of many chemical terms can be shown using chemical equations. Which terms can be shown by an equation that includes the formation of a positive ion?

Electrochemistry

Which of these molecules has no overall dipole moment?

Chemical bonding

Carbon is found in a number of different forms. Buckminsterfullerene and graphene are two of these forms. Buckminsterfullerene is a fullerene allotrope of carbon. Which of the statements about buckminsterfullerene and graphene are correct?

Chemical bonding

Carbon monoxide reacts easily with oxygen to produce carbon dioxide. What conclusion does this information imply?

Electrochemistry

Cars are fitted with catalytic converters that eliminate pollutants from the exhaust gases. Some of the reactions involved need oxygen, and this oxygen is taken from the air. Which exhaust pollutants will react with oxygen on the catalyst surface of the catalytic converter?

Hydrocarbons

Chlorine reacts with sodium hydroxide in two different ways, depending on the temperature. reaction 1: $\text{Cl}_2 + 2\text{OH}^- \rightarrow \text{Cl}^- + \text{ClO}^- + \text{H}_2\text{O}$ reaction 2: $3\text{Cl}_2 + 6\text{OH}^- \rightarrow 5\text{Cl}^- + \text{ClO}_3^- + 3\text{H}_2\text{O}$ Which of the following statements about these reactions is correct?

Electrochemistry

Which of the reactions below shows the organic compound being oxidised by the reagent given?

Electrochemistry

With the apparatus arranged as shown, an orange precipitate is produced in test-tube Z. Compound Q is heated with acidified potassium dichromate(VI), and the vapour then travels into test-tube Z, which contains 2,4-dinitrophenylhydrazine reagent. What might compound Q be?

Carbonyl compounds

Chlorofluoroalkanes that move into the stratosphere are decomposed by ultraviolet radiation. Radicals are formed, and these lead to ozone depletion. What radicals are these?

Reaction kinetics

$10\,\text{cm}^3$ of ethane is reacted with $45\,\text{cm}^3$ of oxygen when the pressure is $101\,\text{kPa}$ and the temperature is $200\,^{\circ}\text{C}$. The combustion is complete. What total volume of gas is present once the reaction has finished, under the same conditions?

Atoms, molecules and stoichiometry

A blend of the three isomers of $\text{C}_2\text{H}_2\text{Cl}_2$ is polymerised. Which arrangements will be present in the polymer chains?

Chemical bonding

The following two reactions are given. $\text{H}_2(g) \rightarrow 2\text{H}(g)$ $\text{CO}(g) + \tfrac{1}{2}\text{O}_2(g) \rightarrow \text{CO}_2(g)$ When molar quantities are taken, how may the two energy changes linked to these reactions be identified?

Chemical energetics

The diagram illustrates the Boltzmann energy distribution curves for molecules in a gas sample at two different temperatures. Which letter on the axes indicates the most probable energy for molecules in that same gas sample at the lower temperature?

Reaction kinetics

For the reaction shown, what units does $K_p$ have? $\text{H}_2\text{O}(g) + \text{C}(s) \rightleftharpoons \text{H}_2(g) + \text{CO}(g)$

Equilibria

For this question, balance the chemical equation by using changes in oxidation numbers. An acidified solution of potassium dichromate(VI) can oxidise a solution containing $\text{V}^{2+}$ ions. The reaction equation is given below. $a\,\text{Cr}_2\text{O}_7^{2-} + b\,\text{V}^{2+} + c\,\text{H}^+ \rightarrow d\,\text{Cr}^{3+} + e\,\text{VO}_3^- + f\,\text{H}_2\text{O}$ What is the value of the ratio $a : b$ in the balanced equation?

Electrochemistry

An argon gas sample has a mass of $0.20\,\text{g}$, with a pressure of $100\,000\,\text{Pa}$ and a temperature of $12\,^{\circ}\text{C}$. What volume does the gas occupy?

States of matter

Which carbon allotrope has all electrons localised?

Chemical bonding

For which reaction does an element experience the greatest change in oxidation number?

Electrochemistry

The decomposition of $\text{PCl}_5$ is represented below. $\text{PCl}_5(g) \rightleftharpoons \text{PCl}_3(g) + \text{Cl}_2(g)$ A container with volume $1\ \text{dm}^3$ is filled with $1.0$ mol of $\text{PCl}_5(g)$, $1.0$ mol of $\text{PCl}_3(g)$ and $1.0$ mol of $\text{Cl}_2(g)$, then left at $250\,^{\circ}\text{C}$ until equilibrium is established. When equilibrium is reached at this temperature, the mixture contains $1.8$ moles of $\text{PCl}_3$. Determine the value of $K_c$ at $250\,^{\circ}\text{C}$?

Equilibria

The fifth to eighth ionisation energies of four elements in Period $3$ of the Periodic Table are shown. Which row corresponds to chlorine?

The Periodic Table: chemical periodicity

Magnesium nitrate, $\text{Mg(NO}_3)_2$, breaks down when heated to produce a white solid and a mixture of gases. One of the gases given off is an oxide of nitrogen, $X$. $7.4\ \text{g}$ of anhydrous magnesium nitrate is heated until no further change takes place. What mass of $X$ is formed?

Atoms, molecules and stoichiometry

Which statement accounts for iodine being less volatile than chlorine?

Group 17

Ammonium carbonate is a crystalline solid. When it is heated gently, a reaction takes place and ammonia is produced as one product. What is happening to the carbonate ions in this reaction?

Equilibria

A single molecule of an oxide of element Z reacts with six molecules of water to form an acidic compound. Identify element Z.

The Periodic Table: chemical periodicity

Which property gets larger from magnesium to barium?

Group 2

A test-tube containing HBr(g) and another separate test-tube containing HI(g) are both heated to the same temperature. Which set of observations could be seen?

States of matter

Many modern cars have catalytic converters installed in the exhaust system. Which three gases does a catalytic converter remove?

Reaction kinetics

An ore of copper contains $3.00\%$ copper carbonate, $\text{CuCO}_3$, by mass. What mass of copper can be obtained from $1$ tonne of this ore?

Atoms, molecules and stoichiometry

The structure of compound X is displayed. X is reacted separately with NaOH(aq) and LiAlH$_4$ to produce Y and Z. Identify Y and Z.

Carboxylic acids and derivatives

The table lists the molecular formulae for three molecules, P, Q and R. None of these molecules is cyclic. P: CH$_4$O Q: CH$_2$O$_2$ R: CH$_2$O Which of these molecules has a strong absorption in the region from $1610\ \text{cm}^{-1}$ to $1750\ \text{cm}^{-1}$ in its infra-red spectra?

Chemical bonding

Which row correctly identifies the mechanism type for each of these two reactions? C$_2$H$_5$Br + KCN CH$_3$COCH$_3$ + HCN

An introduction to AS Level organic chemistry

Ester X is displayed. Ester X: CH$_3$CO$_2$(CH$_2$)$_7$CH$_3$ Ester X is hydrolysed in aqueous sodium hydroxide. What is the molecular formula of one of the products?

Carboxylic acids and derivatives

What reagent could be used to tell propane-1,2-diol apart from ethane-1,2-diol?

Hydroxy compounds

When reacted with hot concentrated acidified potassium manganate(VII), which substance produces propanoic acid as one of the products?

Hydrocarbons

The structure of damascenone is displayed. When damascenone itself is included, how many stereoisomers are possible for this structural formula?

Chemical bonding

What is the total number of isomeric esters for the molecular formula $\text{C}_4\text{H}_8\text{O}_2$?

Carboxylic acids and derivatives

When ethene reacts with aqueous bromine, two products are formed, $\text{CH}_2\text{BrCH}_2\text{Br}$ and $\text{CH}_2\text{BrCH}_2\text{OH}$. Which statement about these products is correct?

Hydroxy compounds

PVC is used as a packaging material. What keeps the different polymer strands joined together in a piece of solid PVC?

Chemical bonding

The Haber process, with a catalyst present, can be used to show ammonia formation as the equation below. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g) \qquad \Delta H = -92\ \text{kJ mol}^{-1}$ Which change in conditions would raise both the speed of ammonia production and the equilibrium amount of ammonia?

Equilibria

The diagram illustrates the structure of buta-1,3-diene. The addition reaction of buta-1,3-diene with two molecules of hydrogen bromide can give three structurally isomeric products. How many of these products contain at least one chiral centre?

Chemical bonding

Researchers are attempting to make a new element with proton number 119. The element is expected to be a Group 1 element in Period 8 of the Periodic Table. Which of the following predictions are likely to be true for this element?

The Periodic Table: chemical periodicity

Which reactions would produce the reaction profile shown?

Chemical energetics

Which factors may cause the rate of a reaction to rise?

Reaction kinetics

Sodium and fluorine are both reactive elements. Two atoms are described below. Which of the statements about these atoms, and about the ions they can form, are correct?

Chemical bonding

Within the atmosphere, which changes can have sulfur dioxide acting either as a reagent or as a catalyst?

Reaction kinetics

In the HBr molecule, the bond .....P..... is .....Q..... than the bond in the HI molecule. Which pair of words correctly completes the sentence above?

Chemical bonding

Compound X has the structure shown. Which of the following statements about compound X are correct? 1. X will decolourise cold, acidified $\text{KMnO}_4\text{(aq)}$. 2. X produces an orange precipitate with $\text{2,4-DNPH}$ reagent. 3. X does not react with Tollens’ reagent.

Carbonyl compounds

Hydrogen cyanide adds to propanal. Which absorptions would be seen in the infra-red spectrum of the product? 1. a weak peak in the range $2200-2250\ \text{cm}^{-1}$ 2. a strong peak in the range $3200-3600\ \text{cm}^{-1}$ 3. a strong peak in the range $1040-1300\ \text{cm}^{-1}$

Analytical techniques

Which alcohols are not able to be dehydrated to produce alkenes? 1. $\text{CH}_3\text{OH}$ 2. $(\text{CH}_3)_3\text{COH}$ 3. $\text{CH}_3\text{CH(OH)CH}_3$

Hydroxy compounds

In solid sulfur, the particles are $\text{S}_8$ molecules. Which equation shows the standard enthalpy of atomisation of sulfur?

Chemical energetics

A reaction mechanism is illustrated. Which of the following statements about this reaction are correct? 1. Heterolytic bond fission occurs. 2. It is a substitution reaction. 3. $\text{OH}^-$ acts as an electrophile.

Chemical bonding

For this question, use changes in oxidation number to balance a chemical equation. The reaction below takes place when $\text{MnO}_2$ is heated with dilute $\text{H}_2\text{SO}_4$. $a\ \text{MnO}_2 + b\ \text{H}^+ \rightarrow c\ \text{Mn}^{2+} + d\ \text{MnO}_4^- + e\ \text{H}_2\text{O}$ What is the value of the ratio $c:d$ in the balanced equation?

Electrochemistry

For this question, take air to contain $21\%$ oxygen. Under room conditions, what is the smallest volume of air needed to ensure that $10\ \text{cm}^3$ of butane gas undergoes complete combustion?

Atoms, molecules and stoichiometry

When aqueous bromine is shaken with cyclohexane and then left to settle, two separate layers appear. The upper cyclohexane layer becomes coloured, while the lower aqueous layer is almost colourless. What is the most likely reason for this observation?

States of matter

During which change are only temporary dipole-induced dipole forces overcome?

States of matter

When $2$ moles of an alkane undergo complete combustion, $400\ \text{dm}^3$ of carbon dioxide are formed at $301\ \text{K}$ and $1 \times 10^5\ \text{Pa}$. Under these conditions, carbon dioxide may be treated as an ideal gas. What is the formula of the alkane?

Atoms, molecules and stoichiometry

Which particle contains the same number of protons as neutrons and has the electronic structure of $1s^2 2s^2 2p^6 3s^2 3p^6$?

Atomic structure

If solid $\text{KClO}_3$ is heated in the absence of air, a mixture containing two chlorine compounds is produced in a mole ratio of $3:1$. Chlorine is the only element whose oxidation number changes during this reaction. What might the oxidation numbers of chlorine be in the two compounds formed?

Electrochemistry

The following two reactions are given. reaction 1: $\text{X}_2(g) + \text{Y}_2(g) \rightleftharpoons 2\text{XY}(g)$ reaction 2: $\text{XY}(g) \rightleftharpoons \frac{1}{2}\text{X}_2(g) + \frac{1}{2}\text{Y}_2(g)$ For reaction 1, the equilibrium constant, $K_p$, is $0.0052$. What is $K_p$ for reaction 2?

Equilibria

Compound T appears as a white crystalline solid. If a sample of compound T is combined with aqueous sodium hydroxide and warmed, a gas is given off that turns damp red litmus paper blue. Additional testing on a solution of compound T with aqueous barium chloride gives a dense white precipitate that remains insoluble after dilute hydrochloric acid is added to the mixture. What compound is T?

Nitrogen and sulfur

Which property accounts for the trend in the volatility of the elements as they move down Group 17?

States of matter

These statements concern the elements in Group 2. Which statement is the correct one?

Group 2

Which element, on combustion in oxygen, can produce an oxide that acts as a reducing agent?

Electrochemistry

A catalyst in a catalytic converter removes nitrogen oxides from the exhaust gases produced by internal combustion engines. Which row gives the correct answer?

Reaction kinetics

When aqueous silver nitrate is mixed with aqueous barium chloride, a white precipitate forms, and this precipitate dissolves in excess dilute aqueous ammonia to give a colourless solution. If an excess of dilute nitric acid is then added to the colourless solution, a white precipitate, Z, is formed. Identify Z.

Equilibria

Which property increases from calcium to barium as Group 2 is descended?

Group 2

Element X is in Period 3. It reacts quickly with water to produce an alkaline solution. Which statement about the chloride of element X is true?

The Periodic Table: chemical periodicity

Which molecule possesses six bonding electrons?

Chemical bonding

Structural and stereoisomerism need to be taken into account for this question. When HBr reacts with trans-pent-2-ene, how many distinct products are possible?

Hydrocarbons

The structural formula of ester P is shown here. Which compounds are formed when P undergoes hydrolysis with dilute hydrochloric acid?

Carboxylic acids and derivatives

A number of non-cyclic alcohols are not oxidised by warm acidified $\text{MnO}_4^-$ ions. Alcohol X is the one in this group with the smallest molecular mass. How many moles of oxygen are needed for the complete combustion of $1.0\,\text{mol}$ of alcohol X?

Atoms, molecules and stoichiometry

Butanoic acid may be made from 1-bromopropane in two steps by using reagents V and W, as indicated below. $\text{1-bromopropane} \xrightarrow{\text{reagent V}} \text{compound Q} \xrightarrow{\text{reagent W}} \text{butanoic acid}$ What could be reagents V and W?

Organic synthesis

Which statement concerning compound T and compound U is correct?

An introduction to AS Level organic chemistry

The diagram displays the infrared spectrum of an organic compound. What might the identity of this compound be?

Chemical bonding

Which reagent is able to react with both $-\text{OH}$ groups in lactic acid, $\text{CH}_3\text{CH(OH)CO}_2\text{H}$?

Hydroxy compounds

1,2-dibromopropane may be prepared from 1-bromopropane in two steps. Which row is correct?

Halogen compounds

2-methylbut-2-ene reacts with $\text{HBr(g)}$ to give two isomeric products. In this reaction, two positively charged intermediates may be formed. Which diagram represents the more stable of the two positively charged intermediates?

Hydrocarbons

In a school laboratory, the ester ethyl methanoate is made by reacting a carboxylic acid with an alcohol. For this reaction, only $50.0\%$ of the alcohol changes into the ester. What mass of alcohol is required to produce $10.0\,\text{g}$ of the ester?

Atoms, molecules and stoichiometry

Solid carbon dioxide, $\text{CO}_2$, has a structure like that of solid iodine, $\text{I}_2$. Which statement concerning solid $\text{CO}_2$ and solid $\text{SiO}_2$ is correct?

Chemical bonding

The structure of Compound X is shown. What kind of carbonyl group is present, and how many chiral centres does one molecule of X contain?

Carbonyl compounds

Which of the following contain one mole of the underlined substance at room conditions?

Atoms, molecules and stoichiometry

Buckminsterfullerene is a fullerene allotrope of carbon. Which of the following statements about buckminsterfullerene are correct?

Chemical bonding

Gaseous sodium ions may be produced from sodium atoms. $\text{Na(s)} \rightarrow \text{Na}^+(\text{g})$ Which quantities must be used to work out the enthalpy change of formation of $\text{Na}^+(\text{g})$?

Chemical energetics

In industry, the Haber process is used to produce ammonia from hydrogen and nitrogen. $3\text{H}_2 + \text{N}_2 \rightleftharpoons 2\text{NH}_3$ Which statements about the activation energy for this process are correct?

Reaction kinetics

Strontium nitrate is heated strongly for several minutes. Which of the following statements are correct?

Group 2

If each oxide is added to water, which ones do not change the pH?

The Periodic Table: chemical periodicity

Propanal reacts with hydrogen cyanide to make 2-hydroxybutanenitrile. A suitable catalyst for this reaction is sodium cyanide. $\text{CH}_3\text{CH}_2\text{CHO} + \text{HCN} \xrightarrow{\text{NaCN}} \text{CH}_3\text{CH}_2\text{CH(OH)CN}$ Which statements about this catalysed reaction between propanal and hydrogen cyanide are correct?

Reaction kinetics

A reaction mechanism is illustrated. (Reaction scheme showing a cyclic chloroalkane reacting with $\text{OH}^-$ to form an alcohol and $\text{Cl}^-$.) Which of the following statements about this reaction are correct?

Halogen compounds

A specimen of X gives $44\,\text{g}$ of carbon dioxide and $27\,\text{g}$ of water when it undergoes complete combustion. A specimen of Y gives $44\,\text{g}$ of carbon dioxide and $18\,\text{g}$ of water when it undergoes complete combustion. A specimen of Z gives $22\,\text{g}$ of carbon dioxide and $9\,\text{g}$ of water when it undergoes complete combustion. Which substances could be straight chain alkanes?

Atoms, molecules and stoichiometry

The enthalpy changes for two reactions are given below. $\text{K}_2\text{CO}_3(s) + 2\text{HCl}(aq) \rightarrow 2\text{KCl}(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g) \quad \Delta H = -34.0\,\text{kJ mol}^{-1}$ $\text{KHCO}_3(s) + \text{HCl}(aq) \rightarrow \text{KCl}(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g) \quad \Delta H = +32.8\,\text{kJ mol}^{-1}$ Determine the enthalpy change for the reaction shown below. $2\text{KHCO}_3(s) \rightarrow \text{K}_2\text{CO}_3(s) + \text{H}_2\text{O}(l) + \text{CO}_2(g)$

Chemical energetics

Which of the following pairs are structural isomers of one another?

An introduction to AS Level organic chemistry

Nitrogen combines with oxygen to make nitrogen monoxide, $\text{NO}$, and nitrogen dioxide, $\text{NO}_2$. Nitrogen dioxide then reacts with water and also with hydroxide ions. $\text{N}_2(g) + \text{O}_2(g) \rightarrow 2\text{NO}(g)$ $2\text{NO}(g) + \text{O}_2(g) \rightarrow 2\text{NO}_2(g)$ $2\text{NO}_2(g) + \text{H}_2\text{O}(l) \rightarrow \text{HNO}_2(aq) + \text{H}^+(aq) + \text{NO}_3^{-}(aq)$ $2\text{NO}_2(g) + 2\text{OH}^-(aq) \rightarrow \text{NO}_2^{-}(aq) + \text{NO}_3^{-}(aq) + \text{H}_2\text{O}(l)$ What conclusions can be drawn from these equations alone?

Nitrogen and sulfur

Which solution has the smallest $\text{pH}$ value?

Equilibria

Sulfur gives a mass spectrum with the peaks listed below. $m/e$ values and relative abundances are shown. From these data, what relative atomic mass of sulfur can be determined, correct to four significant figures?

Atoms, molecules and stoichiometry

What is the electronic configuration of a lone $\text{Ni}^{2+}$ ion?

Atomic structure

At $200\,^{\circ}\text{C}$, aluminium chloride exists as a gas with $M_r = 267$. How many covalent bonds, dative covalent bonds and lone pairs of electrons are present in one molecule of aluminium chloride at $200\,^{\circ}\text{C}$?

Chemical bonding