Feb/March 2022

The first ionisation energy of potassium, $\mathrm{K}$, is $418\,\text{kJ mol}^{-1}$. The first ionisation energy of strontium, $\mathrm{Sr}$, is $548\,\text{kJ mol}^{-1}$. Which statement assists in explaining why $\mathrm{Sr}$ has a higher first ionisation energy than $\mathrm{K}$?

The Periodic Table: chemical periodicity

The two half-equations are given below. $\text{MnO}_4^- + 2\text{H}_2\text{O} + 3e^- \rightarrow \text{MnO}_2 + 4\text{OH}^-$ $2\text{OH}^- + \text{SO}_3^{2-} \rightarrow \text{SO}_4^{2-} + \text{H}_2\text{O} + 2e^-$ The balanced equation for the reaction of manganate(VII) ions with sulfite ions is written as $u\text{MnO}_4^- + v\text{H}_2\text{O} + w\text{SO}_3^{2-} \rightarrow x\text{MnO}_2 + y\text{SO}_4^{2-} + z\text{OH}^-$ Which of the statements below are correct?

Electrochemistry

Hydrogen peroxide, $\text{H}_2\text{O}_2$, breaks down to produce water and oxygen. Bromide ions catalyse the reaction. first step $2\text{Br}^-(aq) + \text{H}_2\text{O}_2(aq) + 2\text{H}^+(aq) \rightarrow 2\text{H}_2\text{O}(l) + \text{Br}_2(aq)$ second step $\text{H}_2\text{O}_2(aq) + \text{Br}_2(aq) \rightarrow 2\text{Br}^-(aq) + 2\text{H}^+(aq) + \text{O}_2(g)$ Which row is the correct one?

Reaction kinetics

Hydrogen and iodine combine to produce hydrogen iodide in an exothermic reaction. The equation is shown. $\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g)$ At equilibrium, a $1\,\text{m}^3$ reaction vessel contains $\text{H}_2$, $\text{I}_2$ and $\text{HI}$ gases. The temperature is altered so that the total pressure in the $1\,\text{m}^3$ vessel becomes twice as large. What is the effect on the value of $K_p$ and on the position of equilibrium?

Equilibria

Diethylzinc, $(\text{C}_2\text{H}_5)_2\text{Zn}$, is introduced into $\text{NaOH}(aq)$. Two reactions take place. reaction 1 $(\text{C}_2\text{H}_5)_2\text{Zn} + \text{H}_2\text{O} \rightarrow \text{ZnO} + 2\text{C}_2\text{H}_6$ reaction 2 $\text{H}_2\text{O} + \text{ZnO} + 2\text{OH}^- \rightarrow \text{Zn(OH)}_4^{2-}$ For these reactions, which compounds function as Brønsted-Lowry acids?

Equilibria

Which of the following statements about atoms and molecules is correct?

Atoms, molecules and stoichiometry

A Boltzmann distribution for one mole of a gas at temperature $T$ is displayed. A further one mole of the same gas is then introduced, while the gas stays at temperature $T$. Which dotted line represents the distribution after the extra gas has been added?

Reaction kinetics

For the reaction shown, the concentrations of both X and Y are each lowered to one half of their starting values while the total volume of the solution remains unchanged. $\text{X(aq)} + \text{Y(aq)} \rightarrow \text{XY(aq)}$ At the same time, the temperature is raised from $298\,\text{K}$ to $348\,\text{K}$. Which prediction is certainly correct?

Reaction kinetics

A student carried out an investigation on the chloride of a Period 3 element. The student recorded the following observations. "The substance was a white, crystalline solid. It dissolved readily in water to form a solution with pH $12$. When it was put into a test-tube and warmed in a roaring Bunsen flame, the substance only melted after several minutes of heating." What can be inferred from this record?

The Periodic Table: chemical periodicity

The elements in Period 3 and the compounds they form display patterns across the period from sodium to chlorine. Which row is correct?

The Periodic Table: chemical periodicity

The table lists the melting points for $\text{SiO}_2$ and $\text{P}_4\text{O}_6$. $\text{SiO}_2$: $1883\,\text{K}$ $\text{P}_4\text{O}_6$: $297\,\text{K}$ Which statement accounts for the difference in the melting points of $\text{SiO}_2$ and $\text{P}_4\text{O}_6$?

Chemical bonding

What electronic configuration does $\mathrm{Mg}^{2+}$ have?

Atomic structure

Samples with equal masses of $\text{CaCO}_3$, $\text{Ca(NO}_3)_2$, $\text{BaCO}_3$ and $\text{Ba(NO}_3)_2$ are heated so that they decompose thermally. For each experiment, the gas volume formed is recorded under identical conditions. Which compound would give the largest volume of gas?

Atoms, molecules and stoichiometry

Which row correctly compares the solubilities of calcium hydroxide and barium hydroxide, and the thermal stabilities of calcium carbonate and barium carbonate?

Group 2

Which of the following statements about the elements in Group 17 and their compounds is correct?

Group 17

An excess quantity of chlorine was passed into $100\,\text{cm}^3$ of hot $6.0\,\text{mol dm}^{-3}$ sodium hydroxide. How many moles of sodium chloride are formed by the reaction?

Atoms, molecules and stoichiometry

In the Contact process, the product is Z. Which reaction or process produces a gas that is able to neutralise an aqueous solution of Z?

Nitrogen and sulfur

When ammonia, $\text{NH}_3$, is added to water, only a small amount of ammonium ions, $\text{NH}_4^+$, is produced. Which row is the correct one?

Equilibria

For this question, you should take alkenes and cyclic alkanes into account. How many structural isomers of $\text{C}_4\text{H}_8$ are there?

Hydrocarbons

Which compound is able to decolourise $\text{Br}_2\text{(aq)}$?

Hydrocarbons

Alkenes undergo reaction with aqueous hydrogen bromide. This reaction takes place through a carbocation intermediate. The more stable the intermediate is, the more quickly the reaction occurs. Which sequence correctly indicates an increase in the rate of reaction of the alkenes with hydrogen bromide?

Reaction kinetics

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

Halogen compounds

Compound $X$ is made up only of the elements $\mathrm{C}$, $\mathrm{H}$ and $\mathrm{O}$. When $2.00\,\text{g}$ of $X$ is completely combusted, $4.00\,\text{g}$ of carbon dioxide and $1.63\,\text{g}$ of water are produced. What is the empirical formula of $X$?

Atoms, molecules and stoichiometry

The diagram illustrates the structures of three halogenoalkanes P, Q and R. All three, P, Q and R, are capable of hydrolysis. Which row is correct?

Reaction kinetics

A 2.30 g sample of ethanol is reacted with excess aqueous acidified potassium dichromate(VI). The mixture is heated under reflux for one hour. The organic product formed is then obtained by distillation. The product yield is 60.0%. What mass of product is obtained?

Atoms, molecules and stoichiometry

The structure of tartaric acid is shown. Four moles of substance X react with one mole of tartaric acid. What might substance X be?

Hydroxy compounds

Which compound produces both: • an orange precipitate when tested with 2,4-DNPH reagent • and a yellow precipitate with alkaline $I_2(aq)$?

Carbonyl compounds

A student proposes two uses for $\text{LiAlH}_4$. reaction 1 $\text{CH}_3\text{CH}=\text{CH}_2 \xrightarrow[]{\text{LiAlH}_4} \text{CH}_3\text{CH}_2\text{CH}_3$ reaction 2 $\text{CH}_3\text{CO}_2\text{H} \xrightarrow[]{\text{LiAlH}_4} \text{CH}_3\text{CH}_2\text{OH}$ Which of these reactions would produce the product shown?

Carboxylic acids and derivatives

Compound X has a single ester group. The mass percentage of oxygen in X is 27.6%. Which pair of products could be formed on hydrolysis of X?

Carboxylic acids and derivatives

What is the minimum number of carbon atoms in a non-cyclic alkane molecule containing a chiral centre?

Chemical bonding

The sequence shown below is present in a polymer molecule. Which monomer would be able to form this polymer by addition polymerisation?

Polymerisation

Compound Y is warmed using a mild oxidising agent. One of the reaction products then reacts with hydrogen cyanide to produce 2-hydroxybutanenitrile. What is compound Y?

Carbonyl compounds

The diagrams illustrate the structures of lycopene and $\beta$-carotene. During the conversion of lycopene into $\beta$-carotene, how many hydrogen atoms are gained or lost per molecule?

Atoms, molecules and stoichiometry

Which molecule has a dipole moment of zero?

Chemical bonding

Which diagram represents the infrared spectrum of a compound containing both a $\text{C}=\text{O}$ group and an $\text{O}-\text{H}$ group?

Chemical bonding

Which dot-and-cross diagram shows $\mathrm{Al}_2\mathrm{Cl}_6$ correctly?

Chemical bonding

The boiling points for several hydrogen halides are listed. $\mathrm{H\text{-}Cl}$: $188\,\text{K}$, $\mathrm{H\text{-}Br}$: $206\,\text{K}$, $\mathrm{H\text{-}I}$: $238\,\text{K}$. Explain the reason for the trend in boiling point from $\mathrm{HCl}$ to $\mathrm{HI}$?

States of matter

Elements $X$, $Y$ and $Z$ all lie in the first two periods of the Periodic Table. Their Pauling electronegativity values, $E_N$, are given as follows: $X = 1.0$, $Y = 2.1$, $Z = 4.0$. Substances with formulae $XZ$, $YZ$ and $Z_2$ are known to exist. Which row arranges these substances in increasing order of melting point?

Chemical bonding

Reaction 1 is represented by the equation shown here. Reaction 1: $\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 \rightarrow 2\mathrm{CO}_2 + 2\mathrm{C}_2\mathrm{H}_5\mathrm{OH}$. The standard enthalpy changes of combustion, $\Delta H_c^\circ$, are: for $\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6$ it is $a$, and for $\mathrm{C}_2\mathrm{H}_5\mathrm{OH}$ it is $b$, in $\text{kJ mol}^{-1}$. Which expression gives the enthalpy change of reaction 1 correctly?

Chemical energetics

Nitrogen monoxide is an atmospheric pollutant produced in car engines by an endothermic reaction of nitrogen with oxygen. $\text{N}_2(g) + \text{O}_2(g) \rightarrow 2\text{NO}(g)$ Which diagram shows the energy profile that corresponds to this reaction?

Chemical energetics

Fig. 1.1 illustrates the way first ionisation energies change across Period 2.

The Periodic Table: chemical periodicity

The Period 3 oxides listed are: $\text{Na}_2\text{O}$, $\text{Al}_2\text{O}_3$, $\text{P}_4\text{O}_6$, $\text{P}_4\text{O}_{10}$, $\text{SO}_2$, $\text{SO}_3$.

The Periodic Table: chemical periodicity

At room temperature, the hydrogen halides HCl, HBr and HI are all colourless gases.

Group 17

Compounds $J$ and $K$ are present in plant oils.

Organic synthesis

Iodine occurs naturally in compounds across a range of oxidation states.

Electrochemistry

By mass, silicon is the Earth’s crust’s second most plentiful element.

Chemical energetics

Titanium is a transition element in Period 4. In minerals, it is most often encountered as $\text{TiO}_2$.

Chemistry of transition elements

Fig. 4.1 shows compounds F and J.

States of matter

In many chemical syntheses, 2-Chloropropanoic acid, $\text{CH}_3\text{CHClCOOH}$, is employed.

Equilibria

Lidocaine is used as an anaesthetic. Figure 6.1 shows how lidocaine is synthesised.

Carboxylic acids and derivatives