Feb/March 2018

What are the molecular shapes of water and boron trifluoride?

Chemical bonding

Which reaction is not a redox reaction?

Electrochemistry

The reaction of sulfur dioxide with oxygen is reversible. $2\text{SO}_2 + \text{O}_2 \rightleftharpoons 2\text{SO}_3 \qquad \Delta H^{\circ} = -196\,\text{kJ mol}^{-1}$. At what pressure and temperature would the reaction to the left be preferred?

Equilibria

Which statement correctly describes the effect of a catalyst on a reversible reaction?

Reaction kinetics

Which oxide does not dissolve in aqueous sodium hydroxide?

The Periodic Table: chemical periodicity

X, Y and Z are three elements in the third period. When X is reacted with chlorine, a liquid product is formed. When Y reacts with chlorine, a solid product is formed; this dissolves in water to make a solution of pH $7$. When Z reacts with chlorine, a solid product is formed; this dissolves in water to make a solution of pH $6$. Which of these elements conduct electricity well?

The Periodic Table: chemical periodicity

A solution includes both $\text{Mg}^{2+}$(aq) and $\text{Sr}^{2+}$(aq) at identical concentration. The solution is split into two equal parts. To one part, aqueous sodium hydroxide is added a drop at a time. To the other part, dilute sulfuric acid is added a drop at a time. Which row is correct?

Group 2

The volatility of the Group 17 elements, chlorine, bromine and iodine, gets lower as you move down the group. What causes this?

States of matter

Bromine is obtained from sea-water. During the last part of the process, two redox reactions occur. $\text{Br}_2$(aq) $+\ \text{SO}_2$(g) $+\ \text{2H}_2\text{O}$(l) $\rightarrow\ \text{2HBr}$(aq) $+\ \text{H}_2\text{SO}_4$(aq) $\text{2HBr}$(aq) $+\ \text{Cl}_2$(g) $\rightarrow\ \text{Br}_2$(g) $+\ \text{2HCl}$(aq) Which row is the correct one?

Electrochemistry

On burning, sulfur produces a gaseous substance X, which may be oxidised to form a gas Y. Gas Y then reacts with water to give product Z. Which row correctly gives the oxidation states of sulfur in X, Y and Z?

Atoms, molecules and stoichiometry

A single molecule of ammonia reacts with a single molecule of ethyl methanoate, $\text{HCO}_2\text{C}_2\text{H}_5$, giving one molecule of methanamide, $\text{HCONH}_2$, together with just one further molecule, X. When one molecule of methanamide is strongly heated, it breaks down to form one molecule of ammonia and only one additional molecule, Y. What might X and Y be?

Carboxylic acids and derivatives

An atom has the electronic configuration of its two outermost shells as $3s^2 3p^6 3d^5 4s^2$. Which atom is this?

The Periodic Table: chemical periodicity

What kinds of stereoisomerism are displayed by 2,4-dimethylhex-2-ene?

Hydrocarbons

An organic ion that has a carbon atom carrying a negative charge is known as a carbanion. An organic ion that has a carbon atom carrying a positive charge is known as a carbocation. The reaction of aqueous sodium hydroxide with 1-bromobutane follows an $\text{S}_\text{N}2$ mechanism. What happens first in the mechanism?

Halogen compounds

Compound X can be changed into compound Y in one step. What might X be?

Organic synthesis

Which compound gives a reaction with 2,4-dinitrophenylhydrazine reagent but shows no reaction with Tollens’ reagent?

Carbonyl compounds

When answering this question, both structural isomerism and stereoisomerism should be taken into account. The molecular formula of compound X is $\text{C}_5\text{H}_{12}\text{O}$. Compound X: • reacts in alkaline aqueous iodine • may be dehydrated to give only two alkenes. Which compound could X be?

Hydroxy compounds

What volume of hydrogen, at room conditions, is generated when 0.160 g of methanol reacts with an excess of sodium?

Atoms, molecules and stoichiometry

When compound X is heated under reflux with acidified potassium dichromate(VI), a carboxylic acid is formed. Compound X does not react with sodium metal. What might compound X be?

Carbonyl compounds

A reaction takes place when a sample of 1-chloropropane is heated under reflux with sodium hydroxide dissolved in ethanol. Which row is correct?

Halogen compounds

Ethanedioic acid has the formula $\text{HO}_2\text{C}_2\text{O}_2\text{H}$. What would be the formula of aluminium ethanedioate?

Atoms, molecules and stoichiometry

Alcohols, aldehydes and nitriles can each be changed into carboxylic acids. Which descriptions of how they are converted into carboxylic acids are correct?

Organic synthesis

Water for drinking may have dissolved calcium hydrogencarbonate, $\text{Ca(HCO}_3)_2$. How many electrons does a hydrogencarbonate anion contain?

Atomic structure

How many structural isomers with molecular formula $\text{C}_4\text{H}_{10}\text{O}$ show infra-red absorptions at about $1200\ \text{cm}^{-1}$ and also at about $3400\ \text{cm}^{-1}$?

Hydroxy compounds

Compound Q has 40% carbon by mass. Which substance could Q be?

Atoms, molecules and stoichiometry

A container is partly filled with hot water, then sealed and left to cool. Which of the following statements are correct?

States of matter

Ammonia and chlorine react in the gas phase, according to $8\text{NH}_3 + 3\text{Cl}_2 \rightarrow \text{N}_2 + 6\text{NH}_4\text{Cl}$. Which of the following statements are correct?

Atoms, molecules and stoichiometry

In which reactions is $\text{NH}_3$ acting as a Brønsted-Lowry acid?

Equilibria

Chlorine reacts with hot aqueous sodium hydroxide. Which oxidation states are shown by chlorine in the products formed in this reaction?

Electrochemistry

In what different forms can nitrogen be present in compounds?

Nitrogen and sulfur

Poly(ethene) and PVC are both addition polymers. Which of the following statements are correct?

Polymerisation

A precipitate is formed when organic compound X is heated with aqueous silver nitrate. The precipitate then dissolves after concentrated aqueous ammonia is added. Which compound could X be?

Halogen compounds

Propanal reacts with hydrogen cyanide to give 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 of the following statements about the reaction of propanal with hydrogen cyanide are correct?

Carbonyl compounds

In which molecule is there a nitrogen atom whose orbitals are $sp$ hybridised?

Chemical bonding

The structure of lactic acid is shown. Which esters could form when lactic acid is heated?

Carboxylic acids and derivatives

What mass of solid residue results from the thermal decomposition of $4.10\,\text{g}$ of anhydrous calcium nitrate?

Atoms, molecules and stoichiometry

Sodium hydroxide reacts to neutralise an acid. $\text{H}^+ + \text{OH}^- \rightarrow \text{H}_2\text{O}$. For a $11000\,\text{dm}^3$ sample of an aqueous solution, the acid concentration, $[\text{H}^+]$, is $1.26 \times 10^{-3}\,\text{mol dm}^{-3}$. What mass of solid sodium hydroxide is needed to neutralise the acid?

Atoms, molecules and stoichiometry

The gas laws may be represented by the ideal gas equation, $pV = nRT$. A vessel with a volume of $7.00 \times 10^{-3}\,\text{m}^3$ contains $0.960\,\text{g}$ of oxygen gas at a temperature of $30^{\circ}\text{C}$. Assume the gas behaves as an ideal gas. What is the pressure in the vessel?

States of matter

Which equation shows the standard enthalpy change of formation of water?

Chemical energetics

Hess’ Law together with bond energy data may be used to work out the enthalpy change of a reaction. Bromoethane, $\text{CH}_3\text{CH}_2\text{Br}$, can be prepared by reacting ethene with hydrogen bromide. $\text{CH}_2{=}\text{CH}_2 + \text{HBr} \rightarrow \text{CH}_3\text{CH}_2\text{Br}$. What is the enthalpy change for this reaction?

Chemical energetics

The sketch graph plots the first ionisation energies for six consecutive elements in the Periodic Table. The letters do not represent the elements' symbols.

The Periodic Table: chemical periodicity

Carbon and silicon are both elements in Group 14.

Hydrocarbons

Calcium and its compounds are used in a wide range of applications.

Group 2

Cyclohexane is a colourless liquid used industrially to make synthetic fibres. A reaction scheme involving cyclohexane is shown.

Atoms, molecules and stoichiometry

State how the solubilities of Group 2 hydroxides change as you go down the group.

Group 2

Describe how the oxidising reactivity of the halogens $\text{Cl}_2$, $\text{Br}_2$ and $\text{I}_2$ changes down the group. Explain this pattern by referring to $E^\circ(\text{X}_2/\text{X}^-)$ values in the Data Booklet.

Electrochemistry

Hydrogen cyanide, $\text{HCN}$, acts as a weak acid in aqueous solution. $\text{HCN}(aq) \rightleftharpoons \text{H}^+(aq) + \text{CN}^-(aq)$ $K_a = 6.2 \times 10^{-10}\ \text{mol dm}^{-3}$

Nitrogen compounds

State what the term partition coefficient means.

Equilibria

Complete the electronic configuration for a chromium atom. $1s^2 2s^2 2p^6 3s^2$ \dots

Chemistry of transition elements

The apparatus contains a cell that can be used to find a value for the Avogadro constant, $L$.

Electrochemistry

Complete the equations to represent the two kinds of polymerisation. Draw one repeat unit for each polymer and include any extra products. Addition polymerisation: $n\,\text{CH}_2{=}\text{CHCH}_3(g) \rightarrow$ … Condensation polymerisation: $n\,\text{HO}_2\text{CCH}_2\text{CO}_2\text{H}(s) + n\,\text{HOCH}_2\text{CH}_2\text{OH}(l) \rightarrow$ …

Polymerisation

Cumin is a spice used to add flavour to food. Two compounds that contribute to that flavour are cuminaldehyde and cuminyl alcohol.

Organic synthesis

Two molecules of compound F combine under suitable conditions to produce compound G. The data provided for F and G include mass spectral evidence, $^{1}\text{H}$ NMR evidence, and the products obtained when G is heated with dilute sulfuric acid.

States of matter