May/June 2016

Which equation represents the reaction occurring in the standard enthalpy change of atomisation of bromine?

Chemical energetics

The chemical equation for the reaction of carbon monoxide with hydrogen is given below. $\text{CO}(g) + 3\text{H}_2(g) \rightleftharpoons \text{CH}_4(g) + \text{H}_2\text{O}(g)$ What are the units of $K_p$ for this reaction?

Equilibria

Enzymes function as biological catalysts. A large number of enzymes are specific. One example of an enzyme that is specific is glucokinase. Glucokinase plays a part in the metabolism of glucose. What does specificity mean in this context?

Reaction kinetics

What makes the ionic radius of a chloride ion greater than the ionic radius of a sodium ion?

The Periodic Table: chemical periodicity

Elements D and E both belong to Period 3. Within Period 3, element D has the smallest atomic radius. In Period 3, only two elements have a melting point lower than that of element E. Elements D and E combine to produce compound L. Which compound could be L?

The Periodic Table: chemical periodicity

X and Y are each Group 2 metals. Both X and Y make hydroxide compounds, but $X(\text{OH})_2$ dissolves in water more readily than $Y(\text{OH})_2$. When a piece of metal Y is added to cold water, the reaction is very slow, and only a few tiny hydrogen bubbles are visible. What could the identities of X and Y be?

Group 2

The solids sodium chloride and sodium iodide each react with concentrated sulfuric acid at room temperature. For NaCl, the products formed are NaHSO$_4$ and HCl. For NaI, the products formed are NaHSO$_4$, HI, I$_2$, SO$_2$, H$_2$O, S and H$_2$S. Which explanation best accounts for the difference in the products?

Group 17

In certain areas, lime, $\text{Ca(OH)}_2$, is mixed into soil to help crops grow better. Which statement correctly explains why lime improves crop growth?

Equilibria

A rock sample has a mass of $2.00\,\text{g}$. It includes calcium carbonate, with no other basic substances present. It exactly neutralises $36.0\,\text{cm}^3$ of $0.500\,\text{mol dm}^{-3}$ hydrochloric acid. What percentage of the $2.00\,\text{g}$ rock sample is calcium carbonate?

Atoms, molecules and stoichiometry

Which statement regarding the ammonia molecule and/or the ammonium ion is correct?

Chemical bonding

Which reaction does not add to the issue of acid rain?

Nitrogen and sulfur

How many bonds of each type are present in the $\text{Al}_2\text{Cl}_6$ molecule?

Chemical bonding

The diagrams illustrate two distinct compounds. What is: • the total number of structural isomers, including compound 2, that could be produced by adding a second methyl group to the ring of compound 1, • the number of $\pi$ electrons present in each compound?

Chemical bonding

The structural formula for compound X is illustrated below. Identify the name of compound X and state how its boiling point compares with that of butanoic acid?

Carboxylic acids and derivatives

Which two reagents would undergo a redox reaction?

Electrochemistry

The initial propagation stage in the reaction between methane and chlorine is shown below. $\text{CH}_4 + \text{Cl}\cdot \rightarrow \text{CH}_3\cdot + \text{HCl}$ How many distinct first propagation stages are possible in the reaction between pentane and chlorine?

Hydrocarbons

Alcohol Y is oxidised mildly to form product Z. Z gives positive tests with Tollens’ reagent and with 2,4-dinitrophenylhydrazine reagent. What could alcohol Y be?

Hydroxy compounds

A student makes pentan-1-ol by carrying out the alkaline hydrolysis of 1-iodopentane. She warms the reaction mixture very gently for 20 minutes. $\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{I} + \text{OH}^- \rightarrow \text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{OH} + \text{I}^-$ If the student uses 1-chloropentane to prepare the same alcohol, she must alter the reaction conditions. Which change in condition should she make, and what is the correct reason for this change?

Reaction kinetics

Malic acid occurs in apples. Which reagent reacts with all three -OH groups in the malic acid molecule?

Hydroxy compounds

Cyclic esters are referred to as lactones. Delta lactone is used both as a solvent and in producing polyesters. From which compound could delta lactone be formed in a single reaction?

Carboxylic acids and derivatives

Which reagent is not suitable for distinguishing ethanal from propanone?

Carbonyl compounds

The ester $\text{CH}_3\text{CH}_2\text{CH}_2\text{CO}_2\text{CH}_2\text{CH(CH}_3)_2$ underwent hydrolysis in acidic conditions. What organic products are formed in this hydrolysis?

Carboxylic acids and derivatives

Tetraethyl lead, $\text{Pb}(\text{C}_2\text{H}_5)_4$, has been used as a petrol additive. What is the percentage by mass of carbon in tetraethyl lead?

Atoms, molecules and stoichiometry

Geranyl ethanoate occurs in ginger and cocoa, and is used as a perfume in shampoos and soaps. When it reacts with an excess of bromine in an organic solvent, $X$, a bromo-derivative, is formed. Including geranyl ethanoate, how many cis-trans isomers does geranyl ethanoate have, and how many chiral centres does $X$ contain?

Hydrocarbons

$X$ is a particle that contains 18 electrons and 20 neutrons. Which symbol could represent $X$?

Atomic structure

What are the basic assumptions of the kinetic theory when it is applied to an ideal gas?

States of matter

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?

Electrochemistry

A small quantity of water is added to each of the compounds below, and the mixture is warmed. Which compounds will produce an acidic gas?

Carboxylic acids and derivatives

Astatine, At, lies beneath iodine in Group 17 of the Periodic Table. Which of the following statements about At are likely to be correct?

Group 17

What reaction types may happen with 1-bromobutane?

Halogen compounds

The equation represents a reaction in the gas phase. $\text{X(g)} \rightarrow \text{2Y(g)}$ The diagram presents the Boltzmann distribution for a fixed mass of $\text{X(g)}$ at temperature $T$ when no catalyst is present. The line $E_A$ shows the activation energy. Which diagrams correctly illustrate the effect of each of the following changes made separately and independently?

Reaction kinetics

The diagram illustrates the structure of cyclohexene. Which structures might be produced by addition reactions when cyclohexene is the only reactant?

Hydrocarbons

The preparation of 2-hydroxypropanoic acid from ethanol requires a number of stages. $\text{C}_2\text{H}_5\text{OH} \rightarrow \rightarrow \rightarrow \text{CH}_3\text{CH(OH)CO}_2\text{H}$ Which of the following statements about this synthesis are correct?

Organic synthesis

During nuclear reactions, the products formed are not the same elements as those that have reacted. These changes are shown using nuclear equations, for example the one below. $^{235}_{92}\text{U} + ^1_0\text{n} \rightarrow ^{144}_{56}\text{Ba} + ^{89}_{36}\text{Kr} + 3^1_0\text{n}$ The total nucleon (mass) number remains 236, and the total proton number stays 92. In a different nuclear reaction, uranium-238 is made to react with deuterium atoms, $^2_1\text{H}$. An isotope of a new element, J, is produced together with two neutrons. $^{238}_{92}\text{U} + ^2_1\text{H} \rightarrow \text{J} + 2^1_0\text{n}$ Which isotope is J?

Atomic structure

The diagram illustrates the structure of addition polymer, $X$. Which reagents would react with polymer $X$?

Polymerisation

Dicarbon monoxide, $\text{C}_2\text{O}$, occurs in dust clouds in space. This molecule has the structure $\text{C} \equiv \text{C} = \text{O}$. It has no unpaired electrons. What is the number of lone pairs of electrons in one molecule of $\text{C}_2\text{O}$?

Chemical bonding

A white powder is known to consist of a mixture of magnesium oxide and aluminium oxide. $100\,\text{cm}^3$ of $2\,\text{mol dm}^{-3}\,\text{NaOH(aq)}$ is just enough to make the aluminium oxide in $x$ grams of the mixture dissolve. The reaction taking place is $\text{Al}_2\text{O}_3 + 2\text{OH}^- + 3\text{H}_2\text{O} \rightarrow 2\text{Al(OH)}_4^-$. $800\,\text{cm}^3$ of $2\,\text{mol dm}^{-3}\,\text{HCl(aq)}$ is just enough to make all of the oxide in $x$ grams of the mixture dissolve. The reactions taking place are $\text{Al}_2\text{O}_3 + 6\text{H}^+ \rightarrow 2\text{Al}^{3+} + 3\text{H}_2\text{O}$ and $\text{MgO} + 2\text{H}^+ \rightarrow \text{Mg}^{2+} + \text{H}_2\text{O}$. How many moles of each oxide are present in $x$ grams of the mixture?

Atoms, molecules and stoichiometry

At room temperature and pressure, $\text{H}_2\text{O}$ exists as a liquid, whereas $\text{H}_2\text{S}$ exists as a gas. What accounts for this difference?

States of matter

When gaseous phosphorus pentachloride is heated, it breaks down to form gaseous phosphorus trichloride and chlorine. The table lists the bond energies. Bond energies: $\text{P-Cl}$ (in both chlorides): $330\,\text{kJ mol}^{-1}$ $\text{Cl-Cl}$: $242\,\text{kJ mol}^{-1}$ What is the enthalpy change for the decomposition of $\text{PCl}_5$ into $\text{PCl}_3$ and $\text{Cl}_2$?

Chemical energetics

Aqueous solution was made by dissolving a blend of $1.0\,\text{mol}$ of $\text{AgNO}_3$ and $1.0\,\text{mol}$ of $\text{FeSO}_4$ in $1.00\,\text{dm}^3$ of water. After equilibrium had been reached, the mixture contained $0.44\,\text{mol}$ of $\text{Ag}^+(aq)$. $\text{Ag}^+(aq) + \text{Fe}^{2+}(aq) \rightleftharpoons \text{Ag}(s) + \text{Fe}^{3+}(aq)$ Determine the numerical value of $K_c$?

Equilibria

The diagram illustrates the Boltzmann distribution of energies for 1 mole of a gas. The gas may participate in a reaction with an activation energy, $E_a$. Which statement best describes the effect of a rise in temperature?

Reaction kinetics

At a particular temperature, solid ammonium chloride breaks down in a $0.500\,\text{dm}^3$ vessel to produce ammonia and hydrogen chloride. $\text{NH}_4\text{Cl}(s) \rightleftharpoons \text{NH}_3(g) + \text{HCl}(g)$ The starting amount of ammonium chloride was $1.00\,\text{mol}$, and after equilibrium was established, $0.300\,\text{mol}$ of ammonium chloride remained. Calculate the numerical value of $K_c$ for this reaction under these conditions?

Equilibria

Which stage in the free-radical substitution of ethane with chlorine has the lowest activation energy?

Reaction kinetics

When sodium and sulfur combine, sodium sulfide, $\text{Na}_2\text{S}$, is produced. How does the atomic radius and the ionic radius of sodium compare with those of sulfur?

The Periodic Table: chemical periodicity

Solid aluminium chloride sublimes at $178^\circ\text{C}$. Which structure most appropriately represents the species present in the vapour at this temperature?

Chemical bonding

A $0.005\,\text{mol}$ portion of anhydrous calcium carbonate was heated until thermal decomposition was complete, forming $100\,\text{cm}^3$ of gas when measured at a particular temperature and pressure. In a different experiment, also performed at the same temperature and pressure, a $0.005\,\text{mol}$ portion of anhydrous calcium nitrate was fully decomposed by heating. The volume of the gaseous products was then measured. What total volume of gaseous products was produced from the calcium nitrate?

Atoms, molecules and stoichiometry

Ammonia gas, $\text{NH}_3$, combines with hydrogen sulfide gas, $\text{H}_2\text{S}$, to make the salt ammonium sulfide, $(\text{NH}_4)_2\text{S}$. When ammonium sulfide dissolves in water, an orange alkaline solution is produced. $(\text{NH}_4)_2\text{S}(aq) \rightleftharpoons \text{NH}_3(aq) + \text{NH}_4\text{SH}(aq)$ Adding $\text{NaOH}(aq)$ to this solution gives off a gas, $X$. Adding $\text{HCl}(aq)$ to a different portion of the solution produces a gas, $Y$. Which gases are $X$ and $Y$?

Equilibria

A solid, $T$, was added to an excess amount of the liquid $U$. A colourless gas was evolved and a white precipitate formed. The precipitate was not $T$. What might $T$ and $U$ be?

Analytical techniques

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?

Electrochemistry

A surplus of chlorine gas, $\text{Cl}_2$, is bubbled through $60\,\text{cm}^3$ of cold aqueous $0.1\,\text{mol dm}^{-3}$ sodium hydroxide. In another experiment, chlorine gas in excess is bubbled through $60\,\text{cm}^3$ of hot aqueous $0.1\,\text{mol dm}^{-3}$ sodium hydroxide until the reaction no longer continues. What extra amount of sodium chloride is formed in the reaction with hot $\text{NaOH}$ compared with cold $\text{NaOH}$?

Atoms, molecules and stoichiometry

Fluorine and iodine belong to Group 17. Their melting points are not the same because the van der Waals’ forces between molecules have different strengths. Which row is correct?

States of matter

Four electronic configurations are given below. Three of these configurations are for atoms of the elements chlorine, sodium and vanadium. Which electronic configuration is for an atom of a different element?

Atomic structure

Chlorofluorocarbons harm the ozone layer by reacting through a free radical mechanism. The initial step in this process is initiation. Which equation is most likely to represent the initiation step when chlorofluoromethane is involved in such a reaction?

Halogen compounds

Synthetic resins may be produced by polymerising a range of monomers, one of which is prop-2-en-1-ol, $\text{CH}_2=\text{CHCH}_2\text{OH}$. Which structure shows the repeat unit of poly(prop-2-en-1-ol)?

Polymerisation

Oct-1-ene, $\text{CH}_3(\text{CH}_2)_5\text{CH}=\text{CH}_2$, may undergo thermal cracking. Which set of compounds W, X, Y and Z could be formed by thermally cracking oct-1-ene? W: $\text{CH}_2=\text{CH}_2$ X: $\text{CH}_3\text{CH}=\text{CH}_2$ Y: $\text{CH}_3\text{CH}_2\text{CH}_3$ Z: $\text{CH}_2=\text{CHCH}=\text{CH}_2$

Hydrocarbons

A cycloalkene having molecular formula $\text{C}_7\text{H}_{12}$ was oxidised using hot concentrated acidified $\text{MnO}_4^-$. The sole organic product formed was 2-methylhexane-1,6-dioic acid. What is the identity of this cycloalkene?

Hydrocarbons

1-chloro-1-methylcyclohexane is hydrolysed by heating with $\text{NaOH(aq)}$. The reaction pathway is illustrated below. In 1-chloro-1-methylcyclohexane, one carbon atom is attached to three other carbon atoms. What charge does this carbon atom have at point Z?

Halogen compounds

Malic acid occurs in apples. Which reagent would react with only one of the $-\text{OH}$ groups in the malic acid molecule?

Hydroxy compounds

Which organic compound would fail to produce a yellow precipitate with alkaline aqueous iodine or an orange precipitate with 2,4-dinitrophenylhydrazine reagent?

Carbonyl compounds

In which reaction is the organic compound oxidized?

Electrochemistry

When each compound below is heated under reflux with an excess of hot acidified $\text{K}_2\text{Cr}_2\text{O}_7$, how many yield a carboxylic acid? $\text{CH}_3\text{CH}_2\text{CHO}$ $\text{CH}_3\text{COCH}_3$ $\text{CH}_3\text{CH}_2\text{CH}_2\text{OH}$ $\text{CH}_3\text{CH(OH)CH}_3$

Carbonyl compounds

How many isomeric esters, counting structural isomers and stereoisomers, can be formed with the molecular formula $\text{C}_5\text{H}_{10}\text{O}_2$, if methanoic acid is one of the two reactants used?

Carboxylic acids and derivatives

Elements X and Y belong to the same group in the Periodic Table. The table gives the first six ionisation energies of X and Y in $\text{kJ mol}^{-1}$. What might the identities of X and Y be?

The Periodic Table: chemical periodicity

Compound X, $\text{C}_4\text{H}_8\text{O}_2$, contains a straight carbon chain. An aqueous solution of X has an approximate pH of 3. Compound Y, $\text{C}_3\text{H}_8\text{O}$, is a secondary alcohol. X and Y are mixed and reacted in the presence of a small amount of concentrated sulfuric acid to produce Z as the main organic product. Which structural formula represents Z?

Carboxylic acids and derivatives

A gaseous sample of an organic compound, J, with a volume of $10\,\text{cm}^3$ was ignited in excess oxygen. The products contained $20\,\text{cm}^3$ of carbon dioxide and $5\,\text{cm}^3$ of nitrogen. Every gas volume was measured at the same temperature and pressure. What might J be?

Atoms, molecules and stoichiometry

The electronic configurations of three elements, X, Y and Z, are shown here. X: $2,6$ Y: $2,8,1$ Z: $2,8,7$ Which formulae represent compounds that conduct electricity when molten?

Chemical bonding

In this question, it may be assumed that all gases behave ideally. A chemist heats a mixture of nitrogen and oxygen gases in a sealed container at constant temperature until the system attains a dynamic equilibrium containing $\text{N}_2(g)$, $\text{O}_2(g)$ and $\text{NO}(g)$. $\text{N}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{NO}(g)$ The chemist carries out the experiment again at the same temperature, with the same initial amounts of $\text{N}_2(g)$ and $\text{O}_2(g)$, but under a much greater pressure. Which statements about the second experiment at higher pressure are correct?

Equilibria

An ethanol burner may be used to warm water. If the relevant measurements are recorded, a value for the enthalpy of combustion of ethanol can be worked out. The equation $\text{heat transferred} = -mc\Delta T$ is used as part of the calculation. Which symbols are correctly described?

Chemical energetics

The graph shows the first ionisation energies of twenty consecutive elements in the Periodic Table. The letters used here are not the standard symbols for these elements. Which of the following statements about this graph are correct?

The Periodic Table: chemical periodicity

Which properties become larger in the order hydrogen chloride, hydrogen bromide and hydrogen iodide?

Group 17

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

Chemical bonding

Terpinen-4-ol is one of the active ingredients found in tea-tree oil. On the skeletal formula diagram of terpinen-4-ol, the carbon atoms marked 1, 2 and 3 are labelled. Which of these labelled carbon atoms are chiral?

Chemical bonding

Propanal reacts with hydrogen cyanide to give 2-hydroxybutanenitrile. One 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 of the following statements about the reaction of propanal with hydrogen cyanide are correct?

Reaction kinetics

In China, blood glucose concentration, $C_6H_{12}O_6$, is reported in $\text{mmol l}^{-1}$. In Pakistan, blood glucose concentration is reported in $\text{mg dl}^{-1}$. The unit $l$ means a litre ($1\,\text{dm}^3$). The unit $dl$ means a decilitre ($0.1\,\text{dm}^3$). A blood glucose concentration of $18.5\,\text{mmol l}^{-1}$ shows that there is a health problem. What is $18.5\,\text{mmol l}^{-1}$ expressed as $\text{mg dl}^{-1}$?

Atoms, molecules and stoichiometry

Which syntheses will succeed?

Organic synthesis

All four species in this question are isolated and gaseous. Which species is not planar?

Chemical bonding

Argon is a gas used to fill electric light bulbs. In what pressure and temperature conditions will argon act most nearly as an ideal gas?

States of matter

A sample of the volatile liquid X with a mass of $0.10\,\text{g}$ produced $0.025\,\text{dm}^3$ of vapour at $100^{\circ}\text{C}$ and atmospheric pressure. At $0^{\circ}\text{C}$ and atmospheric pressure, $1$ mole of vapour has a volume of $22.4\,\text{dm}^3$. What is the relative molecular mass of X?

Atoms, molecules and stoichiometry

The equation for the complete combustion of propan-1-ol is given below. $\text{CH}_3\text{CH}_2\text{CH}_2\text{OH}(l) + 4\frac{1}{2}\,\text{O}_2(g) \rightarrow 3\text{CO}_2(g) + 4\text{H}_2\text{O}(l)$ Standard enthalpy changes of formation are provided. What is the standard enthalpy change of combustion of propan-1-ol, in $\text{kJ mol}^{-1}$?

Chemical energetics

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?

Electrochemistry

Enthalpy changes, $\Delta H$, may be either positive or negative. Which row is the correct one?

Chemical energetics

Sulfur dioxide acts as a preservative during winemaking. The equations below show the reactions that take place when sulfur dioxide dissolves in water. $\text{H}_2\text{O} + \text{SO}_2 \rightleftharpoons \text{HSO}_3^- + \text{H}^+$ $\text{HSO}_3^- + \text{H}^+ \rightleftharpoons \text{SO}_3^{2-} + 2\text{H}^+$ Which statement about these two reactions is true?

Equilibria

Catalysts are an important part of many industrial processes and biochemical reactions. Which row gives the correct description of the effect of a catalyst on a reversible chemical reaction?

Reaction kinetics

The oxide and chloride of an element $X$ are each combined separately with water. The two solutions formed have the same effect on litmus. Which element could $X$ be?

The Periodic Table: chemical periodicity

Each pair shown below is made up of a sample of two different elements. At room temperature and pressure, each element is in its standard state. Which pair of elements has the same type of chemical bond between its atoms?

Chemical bonding

The solutions of $\text{Mg(NO}_3)_2$ and $\text{Ba(NO}_3)_2$ are treated separately through a sequence of reactions. $\text{Mg(NO}_3)_2(aq) \xrightarrow{\text{sodium carbonate solution}} M \xrightarrow{\text{excess HCl}(aq)} N \xrightarrow{\text{excess NaOH}(aq)} P$ $\text{Ba(NO}_3)_2(aq) \xrightarrow{\text{sodium carbonate solution}} Q \xrightarrow{\text{excess HCl}(aq)} R \xrightarrow{\text{excess NaOH}(aq)} S$ $M$, $N$ and $P$ are magnesium compounds. $Q$, $R$ and $S$ are barium compounds. How many of $M$, $N$, $P$, $Q$, $R$ and $S$ form white precipitates?

Group 2

When anhydrous magnesium nitrate, $\text{Mg(NO}_3)_2$, is heated, it decomposes to produce a white solid and a mixture of two gases $X$ and $Y$. $Y$ is oxygen. Determine the ratio $\dfrac{\text{mass of } X \text{ released}}{\text{mass of } Y \text{ released}}$?

Atoms, molecules and stoichiometry

Steam is passed across heated magnesium, producing compound $J$ and hydrogen. Which of the following is not a property of compound $J$?

Group 2

A pair of students, $P$ and $Q$, had to sketch bar charts to show how the sizes of certain properties of the halogens and their compounds vary. Their sketches are given. The bar charts indicate only the pattern of change, not the real numerical values. Student $P$: solubility of $\text{AgX}(s)$ in $\text{NH}_3(aq)$. Student $Q$: $\Delta H^\circ$ for $\text{H}_2(g) + X_2(g) \rightarrow 2\text{HX}(g)$. Which of the students have produced bar charts that display the trends correctly?

Chemical energetics

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?

Electrochemistry

Which statement does not describe how acid rain affects the environment?

Nitrogen and sulfur

What conditions will make it more likely for a gas to behave more ideally?

States of matter

What is the proper name for the molecule represented by the skeletal formula shown?

An introduction to AS Level organic chemistry

The diagram illustrates the structure of 1,3-butadiene. An addition reaction involving 1,3-butadiene and two molecules of hydrogen bromide can give rise to three structurally isomeric products. How many of these products contain at least one chiral centre?

Chemical bonding

A pineapple-smelling ester may be prepared in the laboratory from butanal by means of this reaction scheme. $\text{CH}_3(\text{CH}_2)_2\text{CHO} \xrightarrow{\text{NaBH}_4} X$ $\text{CH}_3(\text{CH}_2)_2\text{CHO} \xrightarrow{\text{Cr}_2\text{O}_7^{2-}/\text{H}^+} Y$ $X$ and $Y$ react together in the presence of concentrated $\text{H}_2\text{SO}_4$ to produce an ester. What is the structural formula for this ester?

Carboxylic acids and derivatives

On heating with chlorine, the hydrocarbon 2,2-dimethylbutane reacts by free radical substitution. During a propagation step, a free radical X$\bullet$ is produced. $\text{CH}_3\text{CH}_2{-}\text{C}(\text{CH}_3)_2{-}\text{CH}_3 + \text{Cl}\bullet \rightarrow X\bullet + \text{HCl}$ How many different structures of X$\bullet$ can there be?

Hydrocarbons

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?

Electrochemistry

A reaction pathway diagram is displayed. The four reactions that come next are all exothermic. Which reaction would not be expected to have a pathway like this?

Chemical energetics

What volume of oxygen, at room temperature and pressure, is required for the complete combustion of $0.1\,\text{mol}$ of methylpropan-1-ol?

Atoms, molecules and stoichiometry

An unidentified organic compound reacts with sodium to produce a combustible gas as one product, but it does not form a yellow precipitate with alkaline aqueous iodine. What could be a possible identity of the unknown organic compound?

Hydroxy compounds

Which reaction would produce 2-chloropropane in the highest yield?

Halogen compounds

The ester, $\text{CH}_3\text{CH}_2\text{CO}_2\text{CH}_3$, is broken down by boiling it with aqueous sodium hydroxide. What compound is one of the products?

Carboxylic acids and derivatives

What mass of urea, $\text{CO(NH}_2\text{)}_2$, has the same nitrogen mass as $101.1\,\text{g}$ of potassium nitrate?

Atoms, molecules and stoichiometry

Caprolactone is a cyclic ester. Its use in the production of specialist polymers is increasing. From which compound could caprolactone be produced by a single reaction?

Chemical bonding

Compound X contains two elements. One of them has the second-highest first ionisation energy value in its group, and the other has the third-highest first ionisation energy value in its group. Which compounds might compound X be?

The Periodic Table: chemical periodicity

Water shows several unusual physical properties when compared with the other hydrides of Group 16 elements. Some of these properties arise from hydrogen bonding. These intermolecular forces are far stronger in water than in $\text{H}_2\text{S}$, for instance. Which of the following statements are correct?

Chemical bonding

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

Reaction kinetics

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?

Electrochemistry

Why is the first ionisation energy of aluminium lower than that of magnesium?

The Periodic Table: chemical periodicity

Ammonia is a colourless gas produced by the Haber process. Which of the following statements about ammonia are correct?

Chemical bonding

Halogenoalkanes display patterns in both their physical and chemical properties. Which properties increase step by step from $ ext{C}_2 ext{H}_5 ext{Cl}$ to $ ext{C}_2 ext{H}_5 ext{Br}$ to $ ext{C}_2 ext{H}_5 ext{I}$?

Chemical bonding

Ethanal and hydrogen cyanide react together to produce a compound that is used in making acrylic fibres. The reaction mechanism involves cyanide ions. Which of the following statements about this mechanism are correct?

Reaction kinetics

Which compounds produce an orange precipitate when treated with 2,4-dinitrophenylhydrazine reagent?

Carbonyl compounds

Copper has a relative atomic mass of $63.5$. Which chart shows a correct mass spectrum that would give this value?

Atomic structure

The structural formulae for two compounds are given below: $\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{COOH}$ and $\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{CHO}$. Which of these statements about the compounds is correct?

Chemical bonding

Which single atom in the gaseous state contains a total of five electrons in spherically shaped orbitals?

Atomic structure

Carbon and silicon each have the same outer-shell electronic arrangement. Why does a Si-Si bond have less strength than a C-C bond?

Chemical bonding

Methyl isocyanate, $\text{CH}_3\text{NCO}$, is a poisonous liquid that is used in the production of some pesticides. Approximately what angle is made between the bonds around the N atom in a molecule of methyl isocyanate?

Chemical bonding

Methanol can be made by reacting carbon monoxide with hydrogen. $\text{CO(g)} + 2\text{H}_2\text{(g)} \rightarrow \text{CH}_3\text{OH(g)}$ The average bond energies needed are shown below: $E(\text{C} \equiv \text{O}) = 1077\,\text{kJ mol}^{-1}$ $E(\text{C-O}) = 360\,\text{kJ mol}^{-1}$ $E(\text{C-H}) = 410\,\text{kJ mol}^{-1}$ $E(\text{H-H}) = 436\,\text{kJ mol}^{-1}$ $E(\text{O-H}) = 460\,\text{kJ mol}^{-1}$ What is the enthalpy change for this reaction?

Chemical energetics

For the reaction shown, the equilibrium constant, $K_c$, is $2\,\text{mol}^{-2}\text{dm}^6$ at $600\,\text{K}$. $\text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightleftharpoons 2\text{NH}_3\text{(g)}$ Calculate the equilibrium concentration of $\text{NH}_3$ at $600\,\text{K}$ if the equilibrium concentrations of $\text{N}_2$ and $\text{H}_2$ are each $2\,\text{mol dm}^{-3}$?

Equilibria