Oct/Nov 2011

The table below gives the physical properties of three elements, X, Y and Z. Element X: melting point $-7\,^{\circ}\text{C}$, boiling point $59\,^{\circ}\text{C}$, density $3.12\,\text{g cm}^{-3}$. Element Y: melting point $98\,^{\circ}\text{C}$, boiling point $883\,^{\circ}\text{C}$, density $0.97\,\text{g cm}^{-3}$. Element Z: melting point $649\,^{\circ}\text{C}$, boiling point $1107\,^{\circ}\text{C}$, density $1.74\,\text{g cm}^{-3}$. Which elements might X, Y and Z be?

The Periodic Table: chemical periodicity

When iodine vapour is heated together with hydrogen at $450\,^{\circ}\text{C}$, an equilibrium is formed. $\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g) \qquad \Delta H = +53\,\text{kJ mol}^{-1}$ $\text{H}_2$ colourless, $\text{I}_2$ purple, $\text{HI}$ colourless. Which change in conditions would make the purple colour of the equilibrium mixture less intense?

Equilibria

At $500\,\text{K}$, which solid curve would best show the molecular-speed distribution of a gas, if the dotted curve shows the matching distribution for the same gas at $300\,\text{K}$?

States of matter

Butanedioate ions can be dehydrogenated to produce $\textit{trans}$-butenedioate ions. The enzyme fumarase catalyses this reaction. Why is this reaction catalysed more quickly by fumarase?

Reaction kinetics

Which element has the strongest tendency to form certain covalent compounds?

Chemical bonding

A major source of atmospheric carbon dioxide is the thermal decomposition of limestone, during the manufacture of cement and of lime for agricultural use. Each year, cement works roast $1000$ million tonnes of limestone, and a further $200$ million tonnes is roasted in kilns to make lime. Calculate the total annual mass output of carbon dioxide (in million tonnes) from these two processes.

Atoms, molecules and stoichiometry

When a $5.00\,\text{g}$ sample of an anhydrous Group II metal nitrate is heated strongly, its mass decreases by $3.29\,\text{g}$. Which metal does it contain?

Atoms, molecules and stoichiometry

Brine, which is aqueous sodium chloride, is electrolysed using inert electrodes in a cell that is stirred so that the products of electrolysis can react with one another. The cell is kept at a low temperature. Which pair of substances is among the main products?

Electrochemistry

Why does volatility decrease as the halogens are descended in Group VII?

States of matter

Completely eliminating the pollutant sulfur dioxide, $\text{SO}_2$, is challenging for both financial and technical reasons. The amount released from furnace chimneys can be reduced by installing desulfurisation plants. The gases are then scrubbed (washed) with calcium hydroxide so that the $\text{SO}_2$ is removed. What is the principal product formed at first?

Atoms, molecules and stoichiometry

Which of the reactions is endothermic?

Chemical energetics

The Data Booklet may be needed for this question. Lead(IV) chloride oxidises bromide ions to bromine. In this reaction, the $\text{Pb}^{4+}$ ions are reduced to $\text{Pb}^{2+}$ ions. If $6.980\,\text{g}$ of lead(IV) chloride is added to an excess of sodium bromide solution, what mass of bromine would be formed?

Electrochemistry

Answer this question by looking at how $\text{KMnO}_4$ reacts with different functional groups under the conditions given. The diagram illustrates the structure of the naturally occurring molecule cholesterol. Two separate oxidation reactions are performed using different conditions: • cold, dilute acidified $\text{KMnO}_4$ • hot, concentrated acidified $\text{KMnO}_4$ Which statements about the products formed are correct?

Hydroxy compounds

A range of compounds has been used in aerosol sprays, refrigerators and in the manufacture of foamed plastics. Which compound will lead to the greatest ozone depletion?

Halogen compounds

In the general formula of which type of compound is the proportion of hydrogen atoms to carbon atoms greatest?

Hydrocarbons

Y and Z are two selective weed killers that are used very commonly. Which reagent can be used to tell Y apart from Z?

Analytical techniques

What happens in the reaction mechanism between aqueous sodium hydroxide and 1-bromobutane?

Halogen compounds

This question requires use of the Data Booklet. $2.76\,\text{g}$ of ethanol was combined with an excess of aqueous acidified potassium dichromate(VI). The reaction mixture was then heated under reflux for one hour. The organic product was afterwards obtained by distillation. The yield of product was $75.0\%$. What mass of product was collected?

Atoms, molecules and stoichiometry

Energy is liberated in the human body when glucose is oxidised through a complex series of reactions. The Krebs cycle is one stage in this series. In one reaction of the Krebs cycle, fumaric acid is converted into malic acid. $\text{HO}_2\text{CCH=CHCO}_2\text{H} \rightarrow \text{HO}_2\text{CCH(OH)CH}_2\text{CO}_2\text{H}$ Which reagents would be used to carry out this change in the laboratory?

Hydrocarbons

When chlorine reacts with propane under ultraviolet light, two isomeric monochloropropanes, $\text{C}_3\text{H}_7\text{Cl}$, are formed as products. Which statement about this reaction is correct?

Hydrocarbons

An unpleasant-smelling compound present in the human armpit is 3-methylhex-2-enoic acid. If this compound is reacted with a cold, dilute, acidified solution of potassium manganate(VII), how many chiral centres will be formed?

Hydroxy compounds

Geraniol is one of the components found in some perfumes. Which statement about geraniol is incorrect?

Hydroxy compounds

Which element has the same number of electron pairs as unpaired electrons in orbitals with principal quantum number $2$?

Atomic structure

Which pair of substances could react to form the ester $\text{CH}_3\text{CH}_2\text{CO}_2\text{CH}_3$?

Carboxylic acids and derivatives

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

Atomic structure

What is the reason that aluminium chloride, $\text{Al}_2\text{Cl}_6$, sublimes at the comparatively low temperature of $180\,^{\circ}\text{C}$?

Chemical bonding

Each of the three statements below is true. Which of them can be explained, at least partly, by hydrogen bonding?

Chemical bonding

A farmer applies lime to soil that has already received an ammonium nitrate fertiliser treatment. Which reactions will take place in the treated soil?

Nitrogen and sulfur

When the sodium salt of a halide reacts with concentrated sulfuric acid, which halide ion, chloride, bromide or iodide, functions as the reducing agent?

Electrochemistry

Within a car engine, the non-metallic element X produces the pollutant oxide Y. Additional oxidation of Y to Z happens spontaneously in the atmosphere. In this additional oxidation, $1\text{ mol}$ of Y reacts with $0.5\text{ mol}$ of gaseous oxygen. Which statements concerning X, Y and Z are correct?

Atoms, molecules and stoichiometry

Disaccharides, $\text{C}_{12}\text{H}_{22}\text{O}_{11}$, play an important role in the human diet. For instance, sucrose occurs in pastries, whereas lactose is present in milk products. Both compounds may undergo hydrolysis. $\text{sucrose} + \text{H}_2\text{O} \rightarrow \text{CH}_2\text{OH(CHOH)}_4\text{CHO} + \text{CH}_2\text{OH(CHOH)}_3\text{COCH}_2\text{OH}$ glucose            fructose $\text{lactose} + \text{H}_2\text{O} \rightarrow \text{CH}_2\text{OH(CHOH)}_4\text{CHO} + \text{CH}_2\text{OH(CHOH)}_4\text{CHO}$ glucose            galactose Which of the following statements about the products of these hydrolysis reactions is/are correct?

Atoms, molecules and stoichiometry

DHA is a colourless liquid that reacts with protein in skin and makes it darken. Its structure is shown. What observations are made when this substance is tested?

Carbonyl compounds

Which compounds yield propanoic acid after acid hydrolysis?

Carboxylic acids and derivatives

Methyl isocyanate, $\text{CH}_3\text{NCO}$, is a poisonous liquid used in making certain pesticides. Within the methyl isocyanate molecule, the atoms are arranged as $\text{H}_3\text{C}-\text{N}=\text{C}=\text{O}$. What is the approximate bond angle between the bonds attached to the N atom?

Chemical bonding

X is an organic compound. X produces a precipitate with aqueous silver nitrate. When an excess of dilute aqueous ammonia is then added, part or all of this precipitate does not dissolve. Which of the following could X be?

Halogen compounds

Under room temperature and pressure, chlorine does not act like an ideal gas. At what temperature and pressure would chlorine’s behaviour become closer to that of an ideal gas?

States of matter

For the reaction $2\text{NF}_3(g) \rightarrow 2\text{N}(g) + 6\text{F}(g)$ the standard enthalpy change is $\Delta H^{\circ} = +1668\,\text{kJ}$. Calculate the bond energy of the N-F bond.

Chemical energetics

When chlorine is heated with aqueous sodium hydroxide, the overall reaction is as follows. $3\text{Cl}_2(aq) + 6\text{NaOH}(aq) \rightarrow 5\text{NaCl}(aq) + \text{NaClO}_3(aq) + 3\text{H}_2\text{O}(l)$ What oxidation numbers does chlorine have in each of the species below?

Electrochemistry

Sulfur dioxide is employed as a preservative in wine making. The equations below show how sulfur dioxide dissolves. $\text{H}_2\text{O} + \text{SO}_2 \rightleftharpoons \text{HSO}_3^- + \text{H}^+$ $\text{HSO}_3^- + \text{H}^+ \rightleftharpoons \text{SO}_3^{2-} + 2\text{H}^+$ Which statement concerning these two reactions is correct?

Equilibria

Aqueous solution was made up with $1.0\,\text{mol}$ of $\text{AgNO}_3$ and $1.0\,\text{mol}$ of $\text{FeSO}_4$ dissolved in $1.00\,\text{dm}^3$ of water. Once equilibrium had been reached, the mixture contained $0.44\,\text{mol}$ of $\text{Ag}^+(aq)$. $\text{Ag}^+(aq) + \text{Fe}^{2+}(aq) \rightleftharpoons \text{Ag}(s) + \text{Fe}^{3+}(aq)$ What is the value of $K_c$?

Equilibria

In the Haber process used to manufacture ammonia, why is the heterogeneous catalyst iron used in a finely divided state?

Reaction kinetics

Hess’s Law may be applied to find the average C-H bond energy in methane. $\Delta H^\circ_{at}$ = standard enthalpy change of atomisation, $\Delta H^\circ_f$ = standard enthalpy change of formation, $\Delta H^\circ_c$ = standard enthalpy change of combustion. Which data values are required to carry out the calculation?

Chemical energetics

The quantity of titanium dioxide present in an ore may be found by means of the following reaction. $3\text{TiO}_2 + 4\text{BrF}_3 \rightarrow 3\text{TiF}_4 + 2\text{Br}_2 + 3\text{O}_2$ Which element has an increase in oxidation number in this reaction?

Electrochemistry

For the reaction $\text{W(aq)} + 2\text{X(aq)} \rightleftharpoons 2\text{Y(aq)} + 3\text{Z(aq)}$, which units are correct for the equilibrium constant $K_c$?

Equilibria

Methyl mercaptan, $\text{CH}_3\text{SH}$, has a very unpleasant odour and is commonly added to natural gas to give it a smell. What products are made when $\text{CH}_3\text{SH}$ burns in excess air?

Nitrogen and sulfur

Nitrogenous fertilisers are widely applied in modern farming. If rainwater carries surplus fertiliser into a nearby lake, eutrophication may take place. Three stages of eutrophication are outlined below. P: Water plants on the lake bed die because they do not receive enough sunlight. Q: Algae grow excessively. R: Oxygen levels fall because bacterial activity becomes excessive. In what order do these three stages occur?

Nitrogen and sulfur

Chlorine may be produced from brine using a diaphragm cell. Which row gives the correct electrodes?

Electrochemistry

Sodium iodide reacts with concentrated sulfuric acid. The equation below shows one of the reactions that occurs. $8\text{NaI} + 9\text{H}_2\text{SO}_4 \rightarrow 8\text{NaHSO}_4 + 4\text{I}_2 + \text{H}_2\text{S} + 4\text{H}_2\text{O}$ Which species has been oxidised in this reaction?

Electrochemistry

The standard enthalpy changes of formation for HCl and HI are $-92\ \text{kJ mol}^{-1}$ and $+26\ \text{kJ mol}^{-1}$ respectively. Which statement is the most significant for accounting for this difference?

Chemical energetics

Lime mortar is prepared from quicklime, water and sand. As time passes, lime mortar turns into a considerably harder substance. Both fresh and old lime mortar react with aqueous hydrochloric acid, but only the old lime mortar effervesces during the reaction. Which equation represents the change from fresh to old lime mortar?

Group 2

$\text{Ar}$, $\text{Ca}^{2+}$ and $\text{K}^+$ each have the same electron count. In what order do their radii increase?

The Periodic Table: chemical periodicity

In the equations below, the letters W, X, Y and Z each stand for whole numbers. Once the equation is correctly balanced, which equation shows that one of W, X, Y or Z has to be 5?

Atoms, molecules and stoichiometry

Bromine reacts with propene in an addition reaction. Which property does the product have?

Hydrocarbons

Buta-1,3-diene is presently produced from fossil fuel sources. In the future, it could be made from ethanol, and ethanol can be produced from non-food agricultural crops. The reaction sequence is shown below: $\text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{step 1}} \text{CH}_3\text{CHO} \xrightarrow{\text{step 2}} \text{CH}_3\text{CH(OH)CH}_2\text{CHO} \xrightarrow{\text{step 3}} \text{CH}_2=\text{CHCH}=\text{CH}_2$ Which term is appropriate for step 1?

Electrochemistry

The Data Booklet may be used for this question. Which bond in the structure shown below has the smallest bond energy?

Chemical bonding

Ethanal, $\text{CH}_3\text{CHO}$, can be reduced with $\text{NaBH}_4$ in aqueous ethanol. This proceeds by nucleophilic addition. What might be the first step in this mechanism?

Chemical bonding

In a reaction sequence, ethanal is transformed into compound H. $\text{CH}_3\text{CHO} \xrightarrow[\text{NaCN}]{\text{HCN}} F \xrightarrow{\text{hot dilute } \text{H}_2\text{SO}_4} G \xrightarrow[\text{trace of conc. } \text{H}_2\text{SO}_4]{\text{CH}_3\text{OH, heat}} H$ What might H be?

Organic synthesis

What does the mechanism of the reaction between aqueous sodium hydroxide and 2-bromo-2-methylbutane involve?

Halogen compounds

The Data Booklet is needed for this question. $2.30\ \text{g}$ of ethanol were reacted with aqueous acidified potassium dichromate(VI). The required product was obtained by immediate distillation with gentle warming. The product yield was $70.0\%$. What mass of product was collected?

Atoms, molecules and stoichiometry

The molecule shown is optically active. How many chiral carbon atoms does this molecule contain?

Chemical bonding

What reagent would be most suitable for telling cyclohexene from cyclohexanol?

Hydrocarbons

Compound $X$ has the molecular formula $\text{C}_4\text{H}_8$ and is changed in the following reactions. $\text{C}_4\text{H}_8\xrightarrow{\text{Br}_2} \text{C}_4\text{H}_8\text{Br}_2 \xrightarrow{\text{aq. NaOH/heat}} \text{C}_4\text{H}_{10}\text{O}_2$ $\text{C}_4\text{H}_8 \xrightarrow{\text{H}_2/\text{Ni}}$ methylpropane State the formula of compound $Z$.

Chemical bonding

Using the Data Booklet is relevant to this question. From which particle is it most difficult to remove an electron?

The Periodic Table: chemical periodicity

How many isomeric alcohols with formula $\text{C}_4\text{H}_9\text{OH}$ produce an alkene that shows cis and trans isomers when treated with conc. $\text{H}_2\text{SO}_4$?

Hydroxy compounds

Which of the following statements about bond angles are correct?

Chemical bonding

An energy profile diagram is displayed. What do the labels on the diagram show?

Chemical energetics

Which statements are assumptions of the kinetic theory of gases and, as a result, of the ideal gas equation, $PV = nRT$?

States of matter

Which characteristics would be predicted for radium, $^{88}\text{Ra}$, or for compounds of it?

Group 2

When a firework is ignited, a fuel reacts with an oxidising agent. In one particular firework, magnesium is the fuel and barium nitrate is the oxidising agent. Which solids are formed when the firework is ignited?

Group 2

Within a car engine, the non-metallic element $X$ produces the pollutant oxide $Y$. Additional oxidation of $Y$ to $Z$ takes place spontaneously in the atmosphere. During this additional oxidation, 1 mol of $Y$ reacts with 0.5 mol of gaseous oxygen. Which of the following statements about $X$, $Y$ and $Z$ are correct?

Nitrogen and sulfur

Compound $X$ has molecular formula $\text{C}_4\text{H}_{10}\text{O}$. Three separate samples of $X$ are each tested with three different reagents. Which set of results could not have been obtained?

Hydroxy compounds

$Y$ is an organic compound. $Y$ forms a precipitate with aqueous silver nitrate. When concentrated aqueous ammonia is then added, the whole of this precipitate dissolves. Which one of the following could be the identity of $Y$?

Halogen compounds

Which compounds will give ethanoic acid after being boiled under reflux with dilute alkali and then acidified?

Carboxylic acids and derivatives

The Data Booklet should be used for this question. $560\,\text{kg}$ of nitrogen and $120\,\text{kg}$ of hydrogen are compressed, heated and then passed over an iron catalyst. Once the gas mixture has reached equilibrium, it contains $96\,\text{kg}$ of hydrogen. What mass of ammonia does it contain?

Equilibria

Which pairs of homologous series share the same C:H ratio in their general formulae?

Atoms, molecules and stoichiometry

The existence of dipoles can account for the fact that the element $\text{Br}_2$ and the compound $\text{CHCl}_3$ are liquids at room temperature. Which kinds of dipole are involved?

States of matter

The table lists the physical properties of three compounds. What could P, Q and R be?

An introduction to AS Level organic chemistry

For the equilibrium $2\text{SO}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{SO}_3(g)$, which factor will alter the value of $K_p$?

Equilibria

Which pollutant, found in the exhaust gases of an internal combustion engine, contains an element with a $+2$ oxidation state and has an odd total number of electrons in a single molecule of the pollutant?

Atoms, molecules and stoichiometry

A factor in the use of sucrose in food processing is osmotic pressure, symbol $\Pi$. For a dilute solution, $\Pi$ changes with concentration in a way similar to gas behaviour. The equation $\Pi V = nRT$ can be used, where $n$ is the number of moles of solute molecules contained in volume $V$ at temperature $T$. The number of moles of solvent molecules should be ignored. In aqueous acidic conditions, sucrose is hydrolysed. $\text{C}_{12}\text{H}_{22}\text{O}_{11} + \text{H}_2\text{O} \rightarrow \text{CH}_2\text{OH(CHOH)}_4\text{CHO} + \text{CH}_2\text{OH(CHOH)}_3\text{COCH}_2\text{OH}$ (sucrose $$ glucose $$ fructose) What can be deduced from this hydrolysis equation?

Atoms, molecules and stoichiometry

Lead(IV) chloride can oxidise bromide ions, forming bromine. In this reaction, the $\text{Pb}^{4+}$ ions are reduced to $\text{Pb}^{2+}$ ions. When $6.980\ \text{g}$ of lead(IV) chloride is mixed with an excess of sodium bromide solution, what mass of bromine is formed?

Atoms, molecules and stoichiometry

Sulfur dioxide is used as a preservative in wine making. The equations below show the way sulfur dioxide dissolves. $\text{H}_2\text{O} + \text{SO}_2 \rightleftharpoons \text{HSO}_3^- + \text{H}^+$ $\text{HSO}_3^- + \text{H}^+ \rightleftharpoons \text{SO}_3^{2-} + 2\text{H}^+$ Which statement about these two reactions is correct?

Equilibria

Butanedioate ions may be dehydrogenated to produce $\text{trans}$-butenedioate ions. The enzyme fumarase catalyses this reaction. Explain why fumarase increases the rate of this reaction?

Reaction kinetics

Aqueous mixture was made by dissolving $1.0\,\text{mol}$ 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 $\text{Ag}^+(\text{aq})$. $\text{Ag}^+(\text{aq}) + \text{Fe}^{2+}(\text{aq}) \rightleftharpoons \text{Ag}(\text{s}) + \text{Fe}^{3+}(\text{aq})$ What is the numerical value of $K_c$?

Equilibria

Which element shows the highest tendency to form some covalent compounds?

Chemical bonding

You may use the Data Booklet for this question. A $5.00\,\text{g}$ sample of an anhydrous Group II metal nitrate is heated strongly and its mass falls by $3.29\,\text{g}$. Which metal is contained in the sample?

Atoms, molecules and stoichiometry

The Data Booklet may be used for this question. One important source of carbon dioxide in the atmosphere is the thermal decomposition of limestone, used in making cement and in producing lime for agricultural use. Cement works roast $1000$ million tonnes of limestone each year, and a further $200$ million tonnes are roasted in kilns to produce lime. Calculate the total annual mass output of carbon dioxide (in million tonnes) from these two processes.

Atoms, molecules and stoichiometry

What causes the halogens to become less volatile as Group VII is descended?

States of matter

Aqueous sodium chloride (brine) is electrolysed using inert electrodes in a cell that is stirred so that the products of electrolysis can react with one another. The cell is maintained at a low temperature. Which pair of substances is produced as one of the main products?

Electrochemistry

To answer this question, think about how $\text{KMnO}_4$ reacts with different functional groups under the conditions given. The diagram gives the structure of cholesterol, a molecule found naturally. The oxidation reactions are carried out separately under different conditions. • cold, dilute acidified $\text{KMnO}_4$ • hot, concentrated acidified $\text{KMnO}_4$ Which of the statements about the products obtained are correct?

Hydrocarbons

Which reaction is the one that is endothermic?

Chemical energetics

Which element possesses the same number of electron pairs as unpaired electrons in orbitals with principal quantum number $2$?

Atomic structure

Completely eliminating the pollutant sulfur dioxide, $\text{SO}_2$, is challenging because of both cost and technical limitations. The amount released from furnace chimneys can be reduced by installing desulfurisation plants. In these plants, the gases are scrubbed (washed) with calcium hydroxide so that the $\text{SO}_2$ is removed. What is the principal product formed at first?

Nitrogen and sulfur

Y and Z are two selective weed killers that are used very widely. Which reagent can be used to tell Y apart from Z?

Analytical techniques

What occurs in the reaction mechanism between aqueous sodium hydroxide and $1$-bromobutane?

Halogen compounds

For which class of compound does the general formula give the greatest ratio of hydrogen atoms to carbon atoms?

Hydrocarbons

A variety of compounds have been used in aerosol sprays, refrigerators and during the manufacture of foamed plastics. Which compound will lead to the greatest ozone depletion?

Halogen compounds

The Data Booklet should be used for this question. $2.76\,\text{g}$ of ethanol was added to an excess of aqueous acidified potassium dichromate(VI). The mixture was then heated under reflux for one hour. The organic product was afterwards obtained by distillation. The percentage yield of product was $75.0\%$. Determine the mass of product that was collected.

Atoms, molecules and stoichiometry

A foul-smelling chemical made in the human armpit is 3-methylhex-2-enoic acid. When this compound reacts with a cold, dilute, acidified solution of potassium manganate(VII), how many chiral centres are formed?

Hydrocarbons

In the human body, glucose is oxidised through a complex series of reactions, and this releases energy. The Krebs cycle is one stage in this series. In one reaction of the Krebs cycle, fumaric acid is changed into malic acid. $\text{HO}_2\text{CCH{=}CHCO}_2\text{H} \rightarrow \text{HO}_2\text{CCH(OH)CH}_2\text{CO}_2\text{H}$ Which reagents could be used to carry out this change in the laboratory?

Hydroxy compounds

When chlorine reacts with propane under ultraviolet light, two isomeric monochloropropanes, $\text{C}_3\text{H}_7\text{Cl}$, are formed as products. Which statement about this reaction is correct?

Halogen compounds

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

Carboxylic acids and derivatives

The table lists the physical properties of three elements, $X$, $Y$ and $Z$. Element $X$: melting point $-7^{\circ}\text{C}$, boiling point $59^{\circ}\text{C}$, density $3.12\ \text{g cm}^{-3}$ Element $Y$: melting point $98^{\circ}\text{C}$, boiling point $883^{\circ}\text{C}$, density $0.97\ \text{g cm}^{-3}$ Element $Z$: melting point $649^{\circ}\text{C}$, boiling point $1107^{\circ}\text{C}$, density $1.74\ \text{g cm}^{-3}$ Which elements might $X$, $Y$ and $Z$ be?

States of matter

Geraniol is a component of some perfumes. Which statement about geraniol is incorrect?

Hydroxy compounds

Chemical equations can be used to show the definitions of many chemical terms. Which term can be illustrated by an equation that shows the formation of a positive ion?

Electrochemistry

All three statements below are true. Which of them can be explained, at least in part, by using hydrogen bonding?

Chemical bonding

Which of the halide ions, chloride, bromide or iodide, behaves as a reducing agent when its sodium salt is reacted with concentrated sulfuric acid?

Electrochemistry

What causes aluminium chloride, $\text{Al}_2\text{Cl}_6$, to sublime at the relatively low temperature of $180^\circ\text{C}$?

Chemical bonding

A farmer puts lime onto land that has already received an ammonium nitrate fertiliser. Which reactions are likely to take place in the treated soil?

Equilibria

In a car engine, the non-metallic element X produces the pollutant oxide Y. Y then undergoes further oxidation to Z spontaneously in the atmosphere. In this extra oxidation, $1\,\text{mol}$ of Y reacts with $0.5\,\text{mol}$ of gaseous oxygen. Which statements about X, Y and Z are correct?

Nitrogen and sulfur

X is an organic compound. When X is treated with aqueous silver nitrate, a precipitate is formed. After adding an excess of dilute aqueous ammonia, part or all of that precipitate does not dissolve. Which substance could X be?

Halogen compounds

Which compounds, on acid hydrolysis, give propanoic acid?

Carboxylic acids and derivatives

Disaccharides, $\text{C}_{12}\text{H}_{22}\text{O}_{11}$, play an important role in the human diet. For instance, sucrose is present in pastries, while lactose is found in milk products. Each of these compounds may be hydrolysed. For sucrose: $\text{sucrose} + \text{H}_2\text{O} \rightarrow \text{CH}_2\text{OH(CHOH)}_4\text{CHO} + \text{CH}_2\text{OH(CHOH)}_3\text{COCH}_2\text{OH}$ (glucose) \hspace{1em} (fructose) For lactose: $\text{lactose} + \text{H}_2\text{O} \rightarrow \text{CH}_2\text{OH(CHOH)}_4\text{CHO} + \text{CH}_2\text{OH(CHOH)}_4\text{CHO}$ (glucose) \hspace{1em} (galactose) Which of the statements below about these hydrolysis products are correct?

Atoms, molecules and stoichiometry

Under room conditions of temperature and pressure, chlorine does not act like an ideal gas. At what temperature and pressure would chlorine’s behaviour be closer to ideal?

States of matter

DHA is a colourless liquid that reacts with protein in the skin, making it darken. Its structure is shown below. $\text{HOCH}_2\text{COCH}_2\text{OH}$ What observations would be seen during tests on this substance?

Carbonyl compounds

Methyl isocyanate, $\text{CH}_3\text{NCO}$, is a poisonous liquid that is used in the production of certain pesticides. Within a methyl isocyanate molecule, the atoms are arranged in the order $\text{H}_3\text{C}-\text{N}=\text{C}=\text{O}$. What is the approximate bond angle between the two bonds around the N atom?

Chemical bonding

If chlorine is warmed with aqueous sodium hydroxide, the overall reaction is as follows. $3\text{Cl}_2(aq) + 6\text{NaOH}(aq) \rightarrow 5\text{NaCl}(aq) + \text{NaClO}_3(aq) + 3\text{H}_2\text{O}(l)$ State the oxidation numbers of chlorine in each of the species below?

Electrochemistry

For the reaction $2\text{NF}_3(g) \rightarrow 2\text{N}(g) + 6\text{F}(g)$ the standard enthalpy change is $\Delta H^{\circ} = +1668\ \text{kJ}$. What is the bond energy for the $\text{N}-\text{F}$ bond?

Chemical energetics

If gaseous iodine is warmed with hydrogen at $450^{\circ}\text{C}$, the system reaches equilibrium. $\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g) \qquad \Delta H = +53\ \text{kJ mol}^{-1}$ $\text{H}_2$: colourless, $\text{I}_2$: purple, $\text{HI}$: colourless. Which alteration in conditions would make the purple colour of the equilibrium mixture less intense?

Equilibria

Which solid-line curve gives the best representation of the molecular-speed distribution for a gas at $500\ \text{K}$, if the dotted-line curve shows the corresponding distribution for the same gas at $300\ \text{K}$?

States of matter