May/June 2015

The diagram illustrates a Boltzmann distribution for the molecular energies in a gaseous mixture. A peak on the diagram is labelled P. What happens when an effective catalyst is added to the mixture?

Reaction kinetics

In an ethene molecule, the double bond joining the two carbon atoms is made up of one $\sigma$ bond and one $\pi$ bond. Which orbitals overlap to produce each of these bonds?

Chemical bonding

The diagram illustrates the reaction pathway for an endothermic reaction. Which arrow shows the activation energy for the forward reaction?

Reaction kinetics

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?

Electrochemistry

The three minerals listed below are found in mines throughout the world. Each is a mixture of two carbonate compounds. They may be used as fire retardants because, when heated, they break down to form $\text{CO}_2$. This gas extinguishes the fire. barytocite: $\text{BaCa(CO}_3)_2$ dolomite: $\text{CaMg(CO}_3)_2$ huntite: $\text{Mg}_3\text{Ca(CO}_3)_4$ In what sequence should their effectiveness as fire retardants be ranked, from most effective to least effective?

Atoms, molecules and stoichiometry

What observations are seen when a sample of silicon chloride, $\text{SiCl}_4$, is placed into a beaker of water?

The Periodic Table: chemical periodicity

The Data Booklet may be needed for this question. Which diagram accurately presents the atomic radii of Mg, Al, Si and P against their melting points?

The Periodic Table: chemical periodicity

Chlorine is used extensively in water treatment plants. What reaction occurs when chlorine dissolves in water?

Equilibria

Astatine, At, is placed underneath iodine in Group VII of the Periodic Table. Which of the following statements is most likely to be correct?

Group 17

Mohr’s salt is a pale green, crystalline substance that dissolves in water. It contains two cations, one of which is $\text{Fe}^{2+}$, together with one anion, $\text{SO}_4^{2-}$. The identity of the second cation was found by warming Mohr’s salt with aqueous sodium hydroxide. A colourless gas was given off, and it dissolved readily in water to produce an alkaline solution. A green precipitate also appeared. What are the identities of the gas and the precipitate?

Nitrogen and sulfur

The Data Booklet may be useful for answering this question. What mass of solid residue is produced when $4.10\,\text{g}$ of anhydrous calcium nitrate undergoes thermal decomposition?

Atoms, molecules and stoichiometry

Which quantity provides the clearest measure of the relative strength of the hydrogen bonds between the molecules in liquid hydrogen halides?

States of matter

With which reagent would compounds P and Q show different observations? P: $\text{HOCH}_2\text{CH(OH)CHO}$ Q: $\text{HOCH}_2\text{COCH}_2\text{OH}$

Carbonyl compounds

Cyclic compound M is heated with dilute hydrochloric acid. Which products are formed in the reaction?

Halogen compounds

Cottonseed oil has a high proportion of polyunsaturated carboxylic acids. During the manufacture of margarine from this oil, the $\text{C=C}$ double bonds in the unsaturated carboxylic acids are hydrogenated. Which reagents and conditions would be suitable for carrying out this hydrogenation reaction?

Chemical bonding

Which intermediate ion is produced in the greatest quantity during the addition of HBr to propene?

Reaction kinetics

Coniine is the principal component of the poison ‘oil of hemlock’. Coniine can be made by reacting ammonia with a dibromo compound, $X$. $\text{NH}_3 + \text{C}_8\text{H}_{16}\text{Br}_2 \rightarrow \text{coniine} + 2\text{HBr}$ What is the name of compound $X$?

Halogen compounds

2-bromopropane is heated with a concentrated solution of sodium hydroxide in ethanol. Which substance is the main product formed in this reaction?

Halogen compounds

The presence of a halogen in an organic compound can be tested by heating the organic compound with aqueous silver nitrate. Which compound would form a precipitate in the shortest time?

Reaction kinetics

Which reagent would produce a different observation when used with compounds $W$ and $X$?

Analytical techniques

In 1869, Ladenburg proposed a structure for benzene, $\text{C}_6\text{H}_6$, with one hydrogen atom bonded to each carbon atom. A compound $\text{C}_6\text{H}_4\text{Cl}_2$ could be made using the same carbon framework as the Ladenburg structure. How many structural isomers does this compound have?

Chemical bonding

The citrus taste of lemons comes from the compound limonene, which is found in both the peel and the juice. What is the mole ratio of carbon dioxide to water formed when limonene is completely burned in oxygen?

Atoms, molecules and stoichiometry

The Data Booklet is needed for this question. $1.00\,\text{g}$ of carbon is burned in a restricted supply of pure oxygen. $0.50\,\text{g}$ of the carbon burns to make $\text{CO}_2$ and $0.50\,\text{g}$ of the carbon burns to make $\text{CO}$. This mixture of $\text{CO}_2$ and $\text{CO}$ is then passed through excess $\text{NaOH(aq)}$, after which the gas that remains is dried and collected. Calculate the volume of the remaining gas. (All gas volumes are measured at $25^\circ\text{C}$ and $1\,\text{atmosphere}$ pressure.)

Atoms, molecules and stoichiometry

Which organic product is obtained when ethanamide, $\text{CH}_3\text{CONH}_2$, is boiled with excess aqueous sodium hydroxide?

Carboxylic acids and derivatives

For this question, the Data Booklet may be used. The isotope $^{99}\text{Tc}$ is radioactive and has been detected in lobsters and seaweed near nuclear fuel reprocessing plants. Which of the following statements about an atom of $^{99}\text{Tc}$ are correct?

Atomic structure

Urea is formed during animal metabolism. It may also be used as a fertiliser. The diagram indicates angle $x$ in this molecule. Which of the following statements about the structure of urea are correct?

Nitrogen compounds

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

Electrochemistry

Why does increasing the pressure of a fixed mass of gaseous reactants at constant temperature make the rate of reaction rise?

Reaction kinetics

Which statements concerning the industrial production of sulfuric acid are correct?

Equilibria

X is in Group II. It makes a sulfate that is more soluble than barium sulfate. It also makes a hydroxide that is more soluble than calcium hydroxide. What could X be?

Group 2

The diagram illustrates the arrangement of an alkene molecule. Which of the following statements about this molecule are correct?

Chemical bonding

An organic compound, X, reacts with calcium metal to form a salt whose empirical formula is $\text{CaC}_4\text{H}_4\text{O}_4$. What might X be?

Carboxylic acids and derivatives

Which compounds undergo reaction with HBr to form the compound R?

Halogen compounds

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?

Electrochemistry

5-hydroxypentanoic acid is easily changed into the cyclic compound L. Which of the following statements about this reaction are correct?

Carboxylic acids and derivatives

This question requires use of the Data Booklet. The ideal gas equation below summarises the gas laws. $pV = nRT$ A mass of $0.96\,\text{g}$ of oxygen gas is enclosed in a glass vessel with a volume of $7.0 \times 10^{-3}\,\text{m}^3$ at a temperature of $30^\circ\text{C}$. Treat the gas as ideal. What pressure is in the vessel?

States of matter

A sealed flask with a volume of $1\,\text{dm}^3$ is used to heat one mole of phosphorus(V) chloride, $\text{PCl}_5$, to $600\,\text{K}$. Once equilibrium has been reached, measurements are recorded. $\text{PCl}_5(g) \rightleftharpoons \text{PCl}_3(g) + \text{Cl}_2(g)$ The experiment is then carried out again, but this time one mole of phosphorus(V) chloride is heated to $600\,\text{K}$ in a sealed flask of volume $2\,\text{dm}^3$. How will the measurements vary?

Equilibria

The standard enthalpy changes of combustion for glucose and ethanol are $-2820$ and $-1368\,\text{kJ mol}^{-1}$, respectively. Glucose, $\text{C}_6\text{H}_{12}\text{O}_6$, can be changed into ethanol. $\text{C}_6\text{H}_{12}\text{O}_6(s) \rightarrow 2\text{C}_2\text{H}_5\text{OH}(l) + 2\text{CO}_2(g)$ Calculate the standard enthalpy change for this reaction?

Chemical energetics

In which reaction does the underlined substance function as a base?

Equilibria

A single molecule of haemoglobin, $\text{Hb}$, is able to combine with four molecules of oxygen, as shown by the equation below. $\text{Hb(aq)} + 4\text{O}_2(aq) \rightleftharpoons \text{Hb(O}_2)_4(aq)$ At equilibrium, when the concentration of $\text{O}_2$ is $7.6 \times 10^{-6}\,\text{mol dm}^{-3}$, the equilibrium concentrations of $\text{Hb}$ and $\text{Hb(O}_2)_4$ are the same. What is the value of $K_c$ for this equilibrium?

Equilibria

Which option shows all three particles having the same electronic configuration and the same number of neutrons?

Atomic structure

Photochromic glass, which is used in sunglasses, turns darker when it is exposed to intense light and becomes clearer again when the light intensity decreases. The degree of darkening depends on the concentration of silver atoms. The reactions below are involved. Reaction 1: $\text{Ag}^+ + \text{Cl}^- \rightleftharpoons \text{Ag} + \text{Cl}$ Reaction 2: $\text{Cu}^+ + \text{Cl} \rightarrow \text{Cu}^{2+} + \text{Cl}^-$ Reaction 3: $\text{Cu}^{2+} + \text{Ag} \rightarrow \text{Cu}^+ + \text{Ag}^+$ Which statement about these reactions is correct?

Equilibria

The Boltzmann distribution shown below represents how molecular energies are spread among the molecules in a gas sample at a particular temperature. Which statement correctly describes how this distribution changes when the temperature is raised?

States of matter

When $3.00\,\text{g}$ of an anhydrous nitrate of a Group II metal undergoes decomposition, $1.53\,\text{g}$ of gas is evolved. What is the nitrate compound?

Atoms, molecules and stoichiometry

What occurs when a strip of magnesium ribbon is put into cold water?

Group 2

When heated, compound X gives off carbon dioxide gas and produces a white solid, Y. Neither X nor Y dissolves in water. Compound Y is used as a refractory lining for kilns. What is compound X?

Group 2

Which diagram accurately displays the electronegativity of the elements Na, Mg, Al and Si plotted against their first ionisation energies?

The Periodic Table: chemical periodicity

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?

Electrochemistry

Which of the following statements about the ammonium ion, $\text{NH}_4^+$, is correct?

Chemical bonding

Carbon monoxide, $\text{CO}$, nitrogen dioxide, $\text{NO}_2$, and sulfur dioxide, $\text{SO}_2$, are all atmospheric pollutants. Which reaction involving these compounds takes place in the atmosphere?

Nitrogen and sulfur

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? $v\text{Cl}_2(g) + w\text{OH}^-(aq) \rightarrow x\text{Cl}^-(aq) + y\text{ClO}_3^-(aq) + z\text{H}_2\text{O}(l)$

Electrochemistry

The shell of a chicken’s egg contributes $5\%$ of the mass of an average egg. The mass of an average egg is $50\text{ g}$. If the egg shell is taken to be pure calcium carbonate, how many complete chicken’s egg shells are needed to neutralise $50\text{ cm}^3$ of $2.0\text{ mol dm}^{-3}$ ethanoic acid?

Atoms, molecules and stoichiometry

Which alcohol is oxidised by an acidified solution of potassium dichromate(VI) to form a ketone with six carbon atoms?

Hydroxy compounds

Which principal product is produced when compound Q is warmed with excess HBr?

Halogen compounds

Students W, X, Y and Z each made the statements below about alkanes and alkenes. W: 'Bromine reacts with alkanes by electrophilic substitution.' X: 'Bromine reacts with alkenes by a free-radical addition mechanism.' Y: 'Alkenes can be oxidised by acidified manganate(VII) ions.' Z: 'Alkenes are formed from alkanes by cracking.' Which two students are correct?

Hydrocarbons

Butanedioic acid can be prepared from 1,2-dibromoethane in two stages. $\text{BrCH}_2\text{CH}_2\text{Br} \xrightarrow{\text{step 1}} X \xrightarrow{\text{step 2}} \text{HO}_2\text{CCH}_2\text{CH}_2\text{CO}_2\text{H}$ Which reagents could be used in this synthesis?

Organic synthesis

Which reaction would not produce propene?

Hydrocarbons

Terpinen-4-ol is one of the active components in tea tree oil. State the molecular formula of terpinen-4-ol?

Atoms, molecules and stoichiometry

Use of the Data Booklet is relevant for this question. $2.40\,\text{g}$ of propan-2-ol was combined with excess acidified potassium dichromate(VI). The reaction mixture was then heated under reflux for twenty minutes. The organic product was afterwards obtained by distillation. The yield of product was $75.0\%$. What mass of product was obtained?

Hydroxy compounds

The diagram illustrates the structure of compound X. What product is formed when compound X reacts with an excess of $\text{NaBH}_4$?

Carbonyl compounds

Lactic acid is found naturally, for instance in sour milk. What is one property of lactic acid?

Equilibria

Citric acid occurs in lemon juice. $\text{HO}_2\text{CCH}_2\text{C(OH)(CO}_2\text{H)CH}_2\text{CO}_2\text{H}$ Calculate the volume of $0.4\,\text{mol dm}^{-3}$ sodium hydroxide solution needed to neutralise a solution containing $0.005\,\text{mol}$ of citric acid?

Atoms, molecules and stoichiometry

Phosphorus can combine with hydrogen to produce phosphine, $\text{PH}_3$. This compound is able to react with a hydrogen ion, $\text{H}^+$. What type of interaction takes place between $\text{PH}_3$ and $\text{H}^+$?

Chemical bonding

Sirolimus is a drug administered to patients following kidney transplants. When Sirolimus reacts with hot aqueous sodium hydroxide, an equimolar mixture of two organic products is formed. What is the structural formula of the product with the lower relative molecular mass?

Carboxylic acids and derivatives

Which of the following statements concerning the phosphide ion, $^{31}_{15}\text{P}^{3-}$, and the chloride ion, $^{35}_{17}\text{Cl}^-$, are correct?

Atomic structure

Why is aluminium chloride, $\text{Al}_2\text{Cl}_6$, able to sublime at the comparatively low temperature of $180\,^\circ\text{C}$?

Chemical bonding

Which statements are true for every exothermic reaction?

Chemical energetics

Which reactions in this list are redox reactions?

Electrochemistry

When these oxides are added to water, which ones will make the water's pH change?

The Periodic Table: chemical periodicity

Halogenated hydrocarbons have many uses. For what purposes have halogenated hydrocarbons been used?

Halogen compounds

In which structure are the four carbon atoms labelled $\text{C}$ all in the same plane?

Chemical bonding

Which of the following statements about 2-methylbutan-1-ol are correct?

Chemical bonding

Propanone and hydrogen cyanide react with one another through this mechanism. Which statements about this mechanism are correct?

Reaction kinetics

Which solid is made up of a simple molecular lattice?

States of matter

Monopotassium citrate is used as an emulsifying agent in powdered milk and in powdered soups. Its formula is shown below. Which of the following statements about monopotassium citrate are correct?

Carboxylic acids and derivatives

The ideal gas equation $pV = nRT$ provides a summary of the gas laws. A methane sample has its volume measured at $60^{\circ}\text{C}$ and $103\text{ kPa}$. The recorded volume is $5.37 \times 10^{-3}\text{ m}^3$. If the gas is assumed to act as an ideal gas, what mass does the methane sample have, correct to two significant figures?

States of matter

Metaldehyde, $(\text{CH}_3\text{CHO})_4$, is employed as a solid fuel in camping stoves. The equation for metaldehyde’s complete combustion is given below. $(\text{CH}_3\text{CHO})_4(s) + 10\text{O}_2(g) \rightarrow 8\text{CO}_2(g) + 8\text{H}_2\text{O}(l)$ $\Delta H_c^{\circ}$ = standard enthalpy change of combustion. Which expression gives the correct value for the enthalpy change of formation of metaldehyde?

Chemical energetics

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?

Electrochemistry

Nitrogen dioxide, $\text{NO}_2$, is in equilibrium with dinitrogen tetroxide, $\text{N}_2\text{O}_4$. $2\text{NO}_2(g) \rightleftharpoons \text{N}_2\text{O}_4(g)$, $\Delta H = -57\text{ kJ mol}^{-1}$ Which conditions lead to the largest percentage of $\text{N}_2\text{O}_4(g)$ at equilibrium?

Equilibria

When a sample of $\text{HI}$ is heated to a specific temperature, the equilibrium shown below is attained. $2\text{HI}(g) \rightleftharpoons \text{H}_2(g) + \text{I}_2(g)$ At this temperature, the partial pressure of $\text{HI}(g)$ is $28$ times that of $\text{H}_2(g)$. Determine the value of $K_p$ at this temperature?

Equilibria

The diagram illustrates the Boltzmann energy distribution curve for molecules in a mixture of two gases at a fixed temperature. For a reaction to take place, the molecules must collide with enough energy. $E_a$ is used to denote the activation energy for the reaction between the gases. From the two values shown, one is the activation energy for a catalysed reaction and the other is for an uncatalysed reaction. Which statement about $E_{a1}$ is correct?

Reaction kinetics

The Data Booklet should be used for this question. $1.00\,\text{g}$ of a metallic element reacts completely with $300\,\text{cm}^3$ of oxygen at $298\,\text{K}$ and $1\,\text{atm}$ pressure to produce an oxide containing $\text{O}^{2-}$ ions. At this temperature and pressure, the volume occupied by one mole of gas is $24.0\,\text{dm}^3$. What could be the identity of the metal?

Atoms, molecules and stoichiometry

This question requires use of the Data Booklet. The ideal gas equation below provides a summary of the gas laws. $pV = nRT$ 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 $0.65\,\text{g}$. Assume that the gas acts as an ideal gas. What might the gas be?

States of matter

Which oxide will form the solution with the highest $\text{pH}$ after being mixed with water?

The Periodic Table: chemical periodicity

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

Electrochemistry

The compound $(\text{CH}_3)_3\text{NaAlCl}_3$ has a simple molecular structure. Which statement concerning $(\text{CH}_3)_3\text{NaAlCl}_3$ is correct?

Chemical bonding

In the laboratory, the labels had come off four bottles. A student noticed that the substance in one of them could be recognised quite easily, since when water was added it would not release fumes of hydrogen chloride. Which one did not produce the $\text{HCl}$ fumes?

Halogen compounds

Transition elements and their compounds are commonly used as catalysts. What is the identity of, and what is the oxidation number of, the element contained in the catalyst used in the Contact process?

Chemistry of transition elements

This question concerns isolated gaseous species. The species $\text{F}^-$, $\text{Ne}$ and $\text{Na}^+$ are isoelectronic, which means that each has the same number of electrons. In what order do their radii increase?

The Periodic Table: chemical periodicity

Because lithium and magnesium have comparable ionic radii, the reactions of lithium and its compounds are very similar to those of magnesium and their corresponding compounds. Which statement about the reactions of lithium or its compounds can be predicted from this statement?

The Periodic Table: chemical periodicity

Two different tests were performed on an aqueous solution of a salt that has only two ions. After each test, the mixtures formed were filtered and the filtrate was collected. Test 1: adding aqueous silver nitrate acidified with dilute nitric acid produces a yellow precipitate, giving filtrate solution $P$. Test 2: adding dilute sulfuric acid produces a white precipitate, giving filtrate solution $Q$. Which ions are present in the filtrates?

Equilibria

Which diagram gives the correct graph of $pV$ versus $n$ for an ideal gas at constant temperature?

States of matter

An organic compound $Z$ • is oxidised by hot acidified potassium manganate(VII), • reacts with sodium to produce hydrogen. What might compound $Z$ be?

Hydroxy compounds

The diagram depicts a molecule containing $\sigma$ bonds and $\pi$ bonds. $\text{CH}_2{=}\text{CH}-\text{CH}_2-\text{C}(=\text{O})-\text{O}-\text{CH}_2-\text{CH}{=}\text{CH}_2$ How many $\sigma$ bonds does this molecule contain?

Chemical bonding

The Finkelstein reaction takes place when NaI in propanone reacts with a chloroalkane or bromoalkane. The halogen is substituted directly by I, and this reaction works only with primary halogenoalkanes. Which halogenoalkane would form compound X?

Reaction kinetics

Ester P has a fruity smell and is shown by the structural formula below. $\text{CH}_3\text{COOCH}_2\text{CH}_2\text{CH}(\text{CH}_3)_2$ Which compounds are formed when P is hydrolysed using hydrochloric acid?

Equilibria

The naturally occurring molecule civetone is present in a gland of the African civet cat and has been used in perfumery. Which reagent would not react with civetone?

Carbonyl compounds

Compound X, $\text{C}_5\text{H}_{12}\text{O}$, undergoes oxidation with acidified sodium dichromate(VI) to form compound Y. Compound Y is then reacted with butan-2-ol, with a small amount of concentrated sulfuric acid present, to produce liquid Z. Give one possible formula for Z.

Carboxylic acids and derivatives

Alkane X has the molecular formula $\text{C}_4\text{H}_{10}$. In sunlight, X reacts with $\text{Cl}_2(g)$ to form only two distinct monochloroalkanes, $\text{C}_4\text{H}_9\text{Cl}$. When each of these monochloroalkanes is heated with ethanolic KOH, the same alkene Y is obtained, and no other organic products are formed. What is formed when Y is treated with hot concentrated acidified $\text{KMnO}_4$?

Hydrocarbons

Aspartame is commonly used as a sweetening agent in ‘diet’ soft drinks. Aspartame is a chiral molecule. (No chiral carbon atoms are present in $\text{C}_6\text{H}_5$.) How many chiral carbon atoms does one molecule of aspartame contain?

An introduction to AS Level organic chemistry

A tertiary bromoalkane, shown here by $>\!\text{C-Br}$, is reacted with aqueous NaOH. The reaction route is given in the mechanism diagram below. Which point in the diagram is labelled correctly?

Reaction kinetics

Separate samples of 1-chlorobutane, 1-bromobutane and 1-iodobutane, four drops of each, were added to three different test-tubes that each contained $1.0\,\text{cm}^3$ of aqueous silver nitrate at $60\,^{\circ}\text{C}$. For all three halogenoalkanes, hydrolysis took place. R stands for the butane chain $\text{C}_4\text{H}_9$ and X stands for the halogen atom. $\text{H}_2\text{O}(l) + \text{R-X}(l) + \text{Ag}^+(aq) \rightarrow \text{R-OH}(aq) + \text{AgX}(s) + \text{H}^+(aq)$ The sequence for how quickly cloudiness appeared in the test-tubes was $\text{RCl} < \text{RBr} < \text{RI}$. Why is this?

Reaction kinetics

In an experiment, a student set out to determine the enthalpy change of combustion of ethane. He took the following values for the standard enthalpy changes of combustion of carbon and hydrogen. $\Delta H_c^{\circ}(\text{carbon}) = -394\,\text{kJ mol}^{-1}$ $\Delta H_c^{\circ}(\text{hydrogen}) = -286\,\text{kJ mol}^{-1}$ From his calculations, the enthalpy change of formation of ethane was found to be $-140\,\text{kJ mol}^{-1}$. What experimental value did he obtain for the standard enthalpy change of combustion of ethane?

Chemical energetics

Malic acid is found in apples. Given suitable conditions, which substance reacts with just one of the $-\text{OH}$ groups in the malic acid molecule?

Hydroxy compounds

The technetium-99 isotope, $^{99}\text{Tc}$, is radioactive and has been detected in lobsters and seaweed close to nuclear fuel reprocessing plants. Which of the following statements about an atom of $^{99}\text{Tc}$ are correct?

Atomic structure

Nitrogen is found in air as covalently bonded diatomic molecules, $\text{N}_2$. Which features does one $\text{N}_2$ molecule have?

Chemical bonding

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?

Electrochemistry

Which physical properties result from hydrogen bonding between water molecules?

Chemical bonding

In atmospheric reactions, which changes involve sulfur dioxide acting as a reagent or as a catalyst?

Nitrogen and sulfur

Astatine, $\text{At}$, is the element located below iodine in Group VII of the Periodic Table. Which of the following statements about $\text{At}$ would be expected to be correct?

Group 17

The diagram displays a molecule of a compound that is used as a flame retardant. Which statements concerning this structure are correct?

Chemical bonding

Which bonding changes take place in the reaction between propanal and hydrogen cyanide?

Chemical bonding

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

Electrochemistry

Which pair includes species that have different shapes?

Chemical bonding

What kinds of reaction does $\text{CH}_2\text{BrCHCH}_2$ undergo?

Halogen compounds

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

Electrochemistry

Which statement may be accounted for by intermolecular hydrogen bonding?

States of matter

Carbon monoxide and methanol can combine to produce ethanoic acid. $\text{CO(g)} + \text{CH}_3\text{OH(l)} \xrightarrow{\Delta H_r^{\circ}} \text{CH}_3\text{CO}_2\text{H(l)}$ The table provides standard enthalpy changes of combustion. What value is obtained for $\Delta H_r^{\circ}$ for the reaction between carbon monoxide and methanol?

Chemical energetics

The reaction below was performed. $\text{HCO}_2\text{CH}_3(aq) + \text{NaOH}(aq) \rightarrow \text{HCO}_2\text{Na}(aq) + \text{CH}_3\text{OH}(aq)$ The concentration of methanol, $[\text{CH}_3\text{OH}(aq)]$, was recorded as time, $t$, passed. Which graph represents the link between $[\text{CH}_3\text{OH}(aq)]$ and $t$?

Reaction kinetics

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

Electrochemistry