Feb/March 2021

The table gives the numbers of protons, neutrons and electrons in four different particles, W, X, Y and Z. Which pair represents atoms of two isotopes of the same element?

Atomic structure

Marble chips are reacted in large excess with $25\,\text{cm}^3$ of $1.0\,\text{mol dm}^{-3}$ hydrochloric acid at $40^{\circ}\text{C}$. What difference is observed when the reaction is repeated using $60\,\text{cm}^3$ of $0.5\,\text{mol dm}^{-3}$ hydrochloric acid at $40^{\circ}\text{C}$?

Atoms, molecules and stoichiometry

The Boltzmann distribution curve for a gaseous mixture of ethene and hydrogen is shown. Nickel is an effective catalyst for the reaction that occurs. How would the diagram be different if the same reaction mixture were at a higher temperature?

Reaction kinetics

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

Halogen compounds

Which row is the correct one?

The Periodic Table: chemical periodicity

Which row gives the correct description of one property of barium and one property of barium oxide?

Group 2

A white anhydrous salt, $Z$, is heated strongly for 30 minutes. Several gases are evolved. The solid left in the test-tube is then dissolved in a small amount of dilute hydrochloric acid. When a few drops of dilute sulfuric acid are added to the test-tube, a white precipitate is produced. Which substance could be $Z$?

Atoms, molecules and stoichiometry

Chlorine gas is treated with aqueous sodium hydroxide. The oxidation number of chlorine changes from $0$ to $-1$ and also from $0$ to $+1$. At what conditions does this reaction take place, and what is the colour of the solid silver salt containing chlorine in oxidation state $-1$?

Electrochemistry

When concentrated sulfuric acid reacts with sodium iodide, the products formed include sulfur, iodine, hydrogen sulfide and sulfur dioxide. Which statement is correct in this case?

Electrochemistry

$\text{NO}$, $\text{NO}_2$, $\text{CO}$ and unburnt hydrocarbons are found in the exhaust gases of internal combustion engines. If catalytic converters are fitted to remove these substances from the exhaust gases, redox reactions take place. What occurs to each compound inside the catalytic converter?

Electrochemistry

Methylamine, $\text{CH}_3\text{NH}_2$, shows chemical behaviour similar to that of ammonia, $\text{NH}_3$. When methylamine reacts with hydrogen chloride, it produces a white crystalline salt called methylammonium chloride. $\text{CH}_3\text{NH}_2 + \text{HCl} \rightarrow \text{CH}_3\text{NH}_3^+\text{Cl}^-$ A sample of methylammonium chloride is warmed with aqueous sodium hydroxide. What products are formed?

Equilibria

In the Periodic Table, where would you place the element whose outer electron shell arrangement is $4s^2 4p^3$?

The Periodic Table: chemical periodicity

The structures of citric acid and isocitric acid are displayed. How many chiral centres are present in each acid?

Chemical bonding

How many tertiary alcohols are there with molecular formula $\text{C}_6\text{H}_{14}\text{O}$?

Hydroxy compounds

The diagram illustrates the structure of a bromo compound that could be produced when bromine reacts with a hydrocarbon. Which row is correct?

Chemical bonding

A section of the structure of strobilurin is shown. $R$ and $R'$ are inert groups. Strobilurin is heated with aqueous sulfuric acid, giving compound $X$. Compound $X$ is then reacted with hydrogen in the presence of a nickel catalyst, giving compound $Y$. What could the structure of compound $Y$ be?

Carboxylic acids and derivatives

Which compound, when refluxed with an acidified solution of potassium dichromate(VI), gives a ketone?

Electrochemistry

Dibromopentanes are able to undergo ‘double elimination’ reactions, forming hydrocarbons. $\text{2NaOH} + \text{C}_5\text{H}_{10}\text{Br}_2 \rightarrow \text{C}_5\text{H}_8 + \text{2NaBr} + \text{2H}_2\text{O}$ Which isomer gives just one hydrocarbon product?

Hydrocarbons

The diagram illustrates how compound $Y$ is formed from compound $X$ in a chemical reaction. $R_1$ and $R_2$ are alkyl groups. $X + \text{HCN} \xrightarrow[{}]{\text{KCN}} Y$ Which row correctly describes this reaction?

Carbonyl compounds

For this question, you may assume that $^1\text{H}$ and $^3\text{H}$ show identical chemical behaviour. A sample of ethanal contains only the hydrogen isotope $^1\text{H}$. It is converted into compound $Z$, $\text{C}_2\text{H}_6\text{O}$, by a nucleophilic addition reaction with NaBH$_4$. Every hydrogen atom in the NaBH$_4$ is the $^3\text{H}$ isotope. $\text{CH}_3\text{CHO} \xrightarrow[]{\text{NaBH}_4} \text{C}_2\text{H}_6\text{O}$ Compound $Z$ is then oxidised to ethanal and water. $\text{C}_2\text{H}_6\text{O} + [O] \rightarrow \text{CH}_3\text{CHO} + \text{H}_2\text{O}$ Which statement about the final product mixture is correct?

Carbonyl compounds

The formula of ethanedioic acid is $\text{HO}_2\text{CCO}_2\text{H}$. What is the formula of aluminium ethanedioate?

Atoms, molecules and stoichiometry

Which reaction produces butanoic acid as one of the products?

Carboxylic acids and derivatives

Substance Q is a hydrocarbon. If $1.00\,\text{g}$ of Q is fully combusted, $3.22\,\text{g}$ of carbon dioxide is formed. What might Q be?

Atoms, molecules and stoichiometry

If reactant $X$ is reacted with an appropriate reagent, the products $Y$ and $Z$ are obtained. Infrared spectra for $X$, $Y$ and $Z$ are displayed. Which row could be right?

Chemical bonding

At $764\,\text{K}$ and $141\,\text{kPa}$, a sample containing $17.15\,\text{mol}\,\text{HI}(g)$ is in dynamic equilibrium with $2.27\,\text{mol}\,\text{H}_2(g)$ and $2.84\,\text{mol}\,\text{I}_2(g)$ in a volume of $1\,\text{m}^3$. $\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g)$ For this mixture, two equilibrium constants, $K_c$ and $K_p$, can be worked out. Which of the following statements about these equilibrium constants is correct?

Equilibria

The energy cycle for the combustion of methane is illustrated here. $\text{CH}_4(g) + 2\text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(l)$ Which of these expressions may be used to work out the energy change, $\Delta H_z$?

Chemical energetics

Many gases do not follow the general gas equation at high pressures. What is the reason for this?

States of matter

Which species is able to accept a lone pair of electrons in order to form a coordinate (dative covalent) bond?

Chemical bonding

A sample with $x\,\text{mol}$ of $\text{Al}_2\text{Cl}_6$ is dissolved in water, producing solution W. To precipitate all of the aluminium as its hydroxide, $y\,\text{mol}$ of sodium hydroxide are needed. Next, more alkali is introduced to make the precipitate dissolve again, forming solution Z. Which of the following statements are correct?

Equilibria

Nitrogen dioxide gas is formed when petrol burns in car engines. Which acids are formed in the atmosphere because nitrogen dioxide is released into the air?

Nitrogen and sulfur

In which reactions is the chief product made by a nucleophilic substitution reaction?

Halogen compounds

An excess of P reacts with Q, in the presence of concentrated sulfuric acid, to produce R. Effervescence is observed when sodium is added to pure R. The structure of P is shown. Which organic compounds could compound Q be?

Hydroxy compounds

There are two carbonyl compounds with the molecular formula $\text{C}_3\text{H}_6\text{O}$. Which reagents produce different observations for these two compounds?

Carbonyl compounds

At first, chemists believed that indium oxide had the formula InO. An experiment showed that $4.8\,\text{g}$ of indium reacted with $1.0\,\text{g}$ of oxygen to form $5.8\,\text{g}$ of indium oxide. The $A_r$ of oxygen was already known to be $16$. Which value for the $A_r$ of indium is obtained from these data?

Atoms, molecules and stoichiometry

An organic compound, T, gives no effervescence when aqueous sodium carbonate is added to it. By mass, compound T is $27.6\%$ oxygen. What could T be?

Carboxylic acids and derivatives

Which substance has intermolecular forces consisting only of temporary dipole-induced dipole attractions?

Chemical bonding

This solution has $0.25\,\text{g}$ of sulfur dioxide dissolved in $1.00\,\text{dm}^3$ of water. What volume of sulfur dioxide, at $50^{\circ}\text{C}$ and a pressure of $1 \times 10^5\,\text{Pa}$, should be introduced into $1.00\,\text{dm}^3$ of water to make this solution?

Atoms, molecules and stoichiometry

An experiment was carried out to find the enthalpy of combustion of ethanol. The recorded data are: mass of water $= W\,\text{g}$; mass of ethanol burned $= X\,\text{g}$; temperature rise $= Y^{\circ}\text{C}$; molar mass of ethanol $= Z\,\text{g mol}^{-1}$; specific heat capacity of water $= 4.2\,\text{J K}^{-1}\text{g}^{-1}$. Which expression may be used to work out the enthalpy of combustion of ethanol in $\text{kJ mol}^{-1}$?

Chemical energetics

$\text{VO}_2\text{Cl}$ reacts with NaI in acidic conditions. $2\text{VO}_2\text{Cl} + 2\text{H}_2\text{SO}_4 + 2\text{NaI} \rightarrow \text{VOCl}_2 + \text{VOSO}_4 + \text{I}_2 + \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O}$ The oxidation state of Cl is $-1$ in $\text{VO}_2\text{Cl}$ and in $\text{VOCl}_2$. Which row describing this reaction is correct?

Electrochemistry

In which reaction does water act as a Brønsted-Lowry base?

Equilibria

Changes in temperature and pressure influence the rate of chemical reactions.

Atoms, molecules and stoichiometry

Chlorine, $\text{Cl}_2$, is a reactive yellow-green gas. It is a powerful oxidising agent.

Group 17

P, Q and R compounds have been detected in the atmosphere of one of Saturn’s moons.

An introduction to AS Level organic chemistry

Hydroxyethanal, $\text{HOCH}_2\text{CHO}$, has been detected in dust clouds close to the centre of our galaxy.

Carbonyl compounds

The oxidation states of cobalt most often encountered are $+2$ and $+3$.

Chemistry of transition elements

Iron(II) compounds are usually stable only in neutral environments that are not oxidising. Finding the lattice energy of $\text{FeO}$ experimentally is difficult.

Chemical energetics

Iodates are compounds containing the IO$_3^-$ anion.

States of matter

Transition elements can make stable complexes with a wide variety of molecules and ions.

Chemistry of transition elements

Carboplatin and satraplatin are anticancer drugs used instead of cisplatin.

Chemistry of transition elements

Fumaric acid is a dicarboxylic acid that occurs naturally. Its structure is shown.

Polymerisation