May/June 2024

Sample X is dissolved in water and then diluted to a final volume of $200\,\text{cm}^3$. The solution obtained has a concentration of $0.100\,\text{mol dm}^{-3}$ HCl. What substance is X?

Atoms, molecules and stoichiometry

For one endothermic reaction, the activation energy has a numerical value equal to twice the enthalpy change of reaction. Which reaction pathway diagram is correct for this reaction?

Chemical energetics

Sodium chromate(VI), $\text{Na}_2\text{CrO}_4$, is produced by strongly heating chromite, $\text{FeCr}_2\text{O}_4$, together with sodium carbonate in an oxidising atmosphere. Chromite contains $\text{Cr}_2\text{O}_4^{2-}$ ions. $2\text{FeCr}_2\text{O}_4 + 4\text{Na}_2\text{CO}_3 + 3\tfrac{1}{2}\text{O}_2 \rightarrow 4\text{Na}_2\text{CrO}_4 + \text{Fe}_2\text{O}_3 + 4\text{CO}_2$ What is happening in this reaction?

Electrochemistry

Oxygen may be generated when potassium manganate(VII), $\text{KMnO}_4$, reacts with hydrogen peroxide, $\text{H}_2\text{O}_2$, in the presence of sulfuric acid, $\text{H}_2\text{SO}_4$. In this reaction, each $\text{H}_2\text{O}_2$ molecule is oxidised by losing two electrons. The remaining products are potassium sulfate, manganese(II) sulfate and water. What number of moles of oxygen gas are formed when $1.0\,\text{mol}$ of $\text{KMnO}_4$ reacts with excess $\text{H}_2\text{O}_2$ under acidic conditions?

Electrochemistry

An alcohol, $\text{ROH}$, undergoes a reversible reaction with ethanoic acid to form an ester. $\text{ROH}(l) + \text{CH}_3\text{COOH}(l) \rightleftharpoons \text{CH}_3\text{COOR}(l) + \text{H}_2\text{O}(l)$ A mixture is made by combining $3.0\,\text{mol}$ of $\text{ROH}$, $2.0\,\text{mol}$ of ethanoic acid and $1.0\,\text{mol}$ of water. When equilibrium is reached, $1.5\,\text{mol}$ of $\text{CH}_3\text{COOR}$ is present. Calculate the equilibrium constant, $K_c$, for this reaction.

Equilibria

Graphs may be plotted to illustrate the percentage of ammonia at equilibrium when nitrogen and hydrogen are combined at different temperatures and pressures. Which diagram correctly shows these two graphs?

Equilibria

The Boltzmann distribution for the hydrogenation of an alkene at a specific temperature when no catalyst is present is shown. Which row gives the correct description of the effects of adding a nickel catalyst to the reaction vessel?

Reaction kinetics

Elements Y and Z are both located in Period 3 of the Periodic Table. When the chloride of element Y is placed in water, it reacts, and a solution with $\text{pH }2$ is formed. When the chloride of element Z is placed in water, it dissolves, and a solution with $\text{pH }7$ is formed. Which statement accounts for these observations?

Chemical bonding

Aluminium, silicon and phosphorus are elements found in Period 3 of the Periodic Table. An oxide is formed by each element. Which row is correct?

The Periodic Table: chemical periodicity

Which of the following statements is correct?

Atoms, molecules and stoichiometry

All of the solubility information in this question refers to the same temperature. The table shows data for calcium compounds and for compounds of X, an element in Group 2 that has not been identified. What is the missing information for element X?

Equilibria

A mixture containing $10\,\text{cm}^3$ of methane and $10\,\text{cm}^3$ of ethane was ignited in excess oxygen. After the products had cooled, the remaining gas was passed into aqueous potassium hydroxide. All gas volumes were taken at the same temperature and pressure. Which volume of gas was absorbed by the alkali?

Atoms, molecules and stoichiometry

What total volume of gas is generated, at room conditions, when $0.010\,\text{mol}$ of anhydrous magnesium nitrate is fully decomposed on heating?

Atoms, molecules and stoichiometry

A solid sodium halide, NaX, is treated with concentrated sulfuric acid. In the products formed, the smallest oxidation state shown by sulfur is $+4$. Halogen $Y_2$ is less volatile than halogen $X_2$. Which sodium halide is NaX, and which halogen is $Y_2$?

Electrochemistry

Q dissolves in water. $Q(aq)$ does not show any reaction with dilute sulfuric acid. A precipitate is formed when aqueous silver nitrate is added to $Q(aq)$. This precipitate is only partly soluble in aqueous ammonia. What might compound Q be?

Group 17

Nitrogen dioxide is a gas that adds to air pollution. It is formed in internal combustion engines. Which statement is correct?

Nitrogen and sulfur

What is the bond angle present in the ammonium ion?

Chemical bonding

Both structural isomerism and stereoisomerism need to be considered when responding to this question. The diagram shows the structure of 3-methylcyclobutene. A sample containing every stereoisomer of 3-methylcyclobutene is reacted with HBr. This gives a mixture of isomeric bromomethylcyclobutanes. How many stereoisomers can 3-methylcyclobutene form, and how many isomeric bromomethylcyclobutanes are in the product mixture?

Hydrocarbons

The diagram illustrates the structure of X. Which row is the correct one?

Chemical bonding

The diagram presents the skeletal formula of citric acid. State the molecular formula of citric acid.

Atoms, molecules and stoichiometry

What reaction takes place when ethane and chlorine are mixed in diffused sunlight?

Halogen compounds

The structure of a geraniol molecule is shown. What product is formed when geraniol reacts with an excess of cold dilute acidified $\text{KMnO}_4$?

Hydrocarbons

Z is a compound made from the two elements X and Y. For element X, there is a very large jump between its 5th and 6th ionisation energies. It has the second largest 1st ionisation energy in its group. For element Y, there is a very large jump between its 6th and 7th ionisation energies. It has the largest 1st ionisation energy in its group. Which compound is Z?

The Periodic Table: chemical periodicity

Q is a halogenoalkane that is either primary or tertiary. It is hydrolysed by aqueous sodium hydroxide. In the first stage of the mechanism for this reaction, two species react with each other. Which row is correct?

Halogen compounds

2-bromopropane is changed into 1,2-dibromopropane by a route with two reactions. reaction 1: 2-bromopropane $\rightarrow$ compound X reaction 2: compound X $\rightarrow$ 1,2-dibromopropane What reagents and conditions are required for the two reactions?

Halogen compounds

Compound X consists of just one pure optical isomer. It is heated in excess concentrated $\text{H}_2\text{SO}_4$. Only a single organic product is produced. Which compound is X?

Hydroxy compounds

What reagents could be used to make 2-bromobutane from butan-1-ol?

Halogen compounds

X is a ketone that is non-cyclic and contains one carbonyl group only, with no other functional groups present. Ketone X shows the following properties: • On reaction with NaBH$_4$, the organic product has an $M_r$ that is 2.3256% greater than the $M_r$ of ketone X. • Ketone X produces a yellow precipitate with alkaline I$_2$(aq). How many isomeric ketones could ketone X be?

Carbonyl compounds

Regarding compound Y: • turns acidified K$_2$Cr$_2$O7$ from orange to green • shows no reaction with Fehling’s reagent • gives an orange precipitate with 2,4-dinitrophenylhydrazine reagent. What is the identity of compound Y?

Carbonyl compounds

The reaction product formed from propanone and hydrogen cyanide is hydrolysed in acidic conditions. What is the formula of the final product?

Carboxylic acids and derivatives

P is a carboxylic acid having molecular formula $\text{C}_5\text{H}_{10}\text{O}_2$. When carboxylic acid P is reacted with an excess of LiAlH$_4$, compound Q is produced. Which pair of molecules could represent carboxylic acid P and compound Q?

Carboxylic acids and derivatives

Compound X is reacted with an excess of dilute aqueous potassium hydroxide. What structure is formed for the organic product?

Halogen compounds

The diagram displays two repeat units of an addition polymer. What monomer formed this polymer?

Polymerisation

Which statement concerning $^{131}_{53}\text{I}$ is correct?

Atomic structure

The relative atomic mass of antimony is 121.76. There are two isotopes of antimony. Their mass numbers are separated by two. The isotope with the lower mass number has the greater abundance. What percentage abundance does the isotope with the higher mass number have?

Atoms, molecules and stoichiometry

When aluminium chloride is heated in the solid state, $\text{Al}_2\text{Cl}_6$ forms. What type of bonding is present in $\text{Al}_2\text{Cl}_6$?

Chemical bonding

The structure of the sulfur dioxide molecule is shown. What shape does the sulfur dioxide molecule have?

Chemical bonding

What is the density of a sample of fluorine gas at $32^\circ\text{C}$ and $100\,000\,\text{Pa}$? Assume that, under these conditions, fluorine behaves as an ideal gas.

States of matter

The graph presents the boiling points of the hydrogen compounds of Group 16 elements. Which statement gives the correct explanation for why water does not follow the pattern shown by the other compounds?

Chemical bonding

A diagram displays an energy cycle. The energy changes involved are X, Y and Z. For energy change Y, the numerical value is either $-890$ or $+890$. For energy change Z, the numerical value is either $-964$ or $+964$. Which of the three values are negative?

Chemical energetics

Which pair of formulae is the right one?

Atoms, molecules and stoichiometry

Which equation corresponds to the standard enthalpy of formation of sodium oxide?

Chemical energetics

Nitrogen dioxide undergoes reaction with water. $2\text{NO}_2 + \text{H}_2\text{O} \rightarrow \text{HNO}_2 + \text{HNO}_3$ Which statement about this reaction is correct?

Nitrogen and sulfur

When phosphorus is reacted with concentrated sulfuric acid, phosphoric acid, sulfur dioxide and water are formed. $a\text{H}_2\text{SO}_4 + b\text{P} \rightarrow c\text{H}_3\text{PO}_4 + d\text{SO}_2 + e\text{H}_2\text{O}$ $a$, $b$, $c$, $d$ and $e$ each represent whole numbers. This equation may be balanced by applying oxidation numbers. Find the value of the total $a + b + c + d + e$?

Electrochemistry

In two experiments, the amount of ammonia formed is recorded as a function of time. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g) \quad \Delta H = -92\,\text{kJ mol}^{-1}$ For experiment 1, $3\,\text{mol}$ of $\text{H}_2(g)$ and $1\,\text{mol}$ of $\text{N}_2(g)$ are allowed to react at $45\,^{\circ}\text{C}$ and under a pressure of $200\,\text{atm}$. A graph of ammonia volume produced against time is drawn. Experiment 2 is then carried out. It is the same as experiment 1 except for one condition. What is different in experiment 2 from experiment 1?

Reaction kinetics

Which reaction has an equilibrium constant, $K_p$, with no units?

Equilibria

At room temperature, gas Q decomposes slowly. $\text{Q}(g) \rightarrow \text{X}(g) + \text{Z}(g)$ Shown is the Boltzmann distribution curve for gas Q at room temperature. Which change happens when a catalyst is added to gas Q?

Reaction kinetics

Which of the statements given is correct?

Atoms, molecules and stoichiometry

A blend of calcium carbonate, calcium nitrate, strontium carbonate and strontium nitrate is thermally decomposed. The decomposition reaction of each substance proceeds to completion. Each substance is anhydrous. How many distinct products are produced?

Group 2

W is a solid which reacts with water to form an alkaline solution. When two drops of dilute $\text{H}_2\text{SO}_4$ are added to this alkaline solution, a white precipitate is formed. What could be the identity of solid W?

Group 2

Chlorine gas is made to react with cold aqueous sodium hydroxide. Which statement about this reaction is correct?

Group 17

What number of molecules are there in $62\,\text{g}$ of solid white phosphorus, $\text{P}_4$?

Atoms, molecules and stoichiometry

Sodium is put into water to make solution Y. The pH of solution Y is then measured. When powdered substance X is added to solution Y, the pH decreases. Which two compounds could each be substance X?

Equilibria

The table gives statements about some properties of halogens and their compounds, together with explanations for those properties. Which row gives a correct statement of the property and a correct explanation for that statement?

Group 17

Which statement gives a description of a property of an ammonium ion?

Chemical bonding

Catalytic converters are installed in the exhaust systems of many cars. Gas X: - leads to acid rain if it is emitted into the air - is taken out of car exhaust fumes by a catalytic converter. What is gas X?

Reaction kinetics

For which class of compound is the hydrogen-to-carbon atom ratio in the general formula the greatest?

Hydrocarbons

Which of the following statements is correct?

Atoms, molecules and stoichiometry

Z is a gaseous hydrocarbon with a density of $3.50 \times 10^{-3}\,\text{g cm}^{-3}$ at room conditions. When Z is treated with an excess of hot concentrated acidified $\text{KMnO}_4$, the reaction produces only one kind of carboxylic acid. What is Z?

Atoms, molecules and stoichiometry

Compound X may be oxidised to form compound Y. Compound Y forms a yellow precipitate with alkaline $\text{I}_2\text{(aq)}$. Which compound is X?

Hydroxy compounds

Aqueous $\text{NaOH}$ reacts with 1-bromopropane to produce propan-1-ol. What needs to be shown in a diagram of the first step in the mechanism?

Chemical bonding

In which reaction does the organic compound undergo oxidation?

Electrochemistry

The graphs display the first eight consecutive ionisation energies for two elements in Period 3 of the Periodic Table. What is the formula of the ionic compound formed by these elements?

The Periodic Table: chemical periodicity

1 mole of each of the four compounds below is reacted separately with: • an excess of sodium • an excess of sodium carbonate. Which compound gives the same volume of gas with both reagents?

Atoms, molecules and stoichiometry

Which chemical reaction can be used to tell propan-1-ol apart from propan-2-ol?

Hydroxy compounds

Compound T is represented by the skeletal formula below. Which of the structures shown is a structural isomer of compound T?

Chemical bonding

The diagram illustrates a simplified structure of coenzyme $\text{Q}_{10}$. Which row gives the correct description of the structure of coenzyme $\text{Q}_{10}$?

Chemical bonding

Limonene, $\text{C}_{10}\text{H}_{16}$, has one 6-membered ring, and this is the sole cyclic part of its structure. What volume of hydrogen, at room conditions, is needed to react completely with the $\text{C=C}$ double bonds in one mole of limonene?

Atoms, molecules and stoichiometry

1-bromopropane undergoes reaction with hot ethanolic $\text{NaOH}$. What is the molecular formula for the product formed in this reaction?

Halogen compounds

A sample of pent-2-en-4-ol, $\text{C}_5\text{H}_{10}\text{O}$, includes every stereoisomer that can exist for this compound. How many stereoisomers does the sample contain?

Chemical bonding

Which pair of reagents combine to produce a product containing a chiral carbon atom?

Chemical bonding

The diagrams illustrate the structures of two esters, X and Y, which are produced in ripening apples. Which carboxylic acids are produced when these esters are hydrolysed by $\text{H}_2\text{SO}_4\text{(aq)}$?

Carboxylic acids and derivatives

An addition polymer is formed from monomer Z. Monomer Z is shown by the structure $\text{CH}_2{=}\text{CH}-\text{C}(=\text{O})-\text{OCH}_2\text{CH}_3$. What structure does the polymer formed from this monomer have?

Chemical bonding

Which pair consists of two species that are both free radicals?

Chemical bonding

Compound X is oxidised by acidified $\text{K}_2\text{Cr}_2\text{O}_7$ to give compound Y. The infrared spectrum for compound Y is shown. A table listing characteristic infrared absorption ranges is given. What is the identity of compound X?

Hydroxy compounds

What shape is correctly predicted by VSEPR theory?

Chemical bonding

In which species is the underlined atom's outer shell not complete?

Chemical bonding

For this question, assume that nitrogen acts as an ideal gas under the conditions given. What volume is taken up by $1.00\,\text{g}$ of nitrogen at $50.0^\circ\text{C}$ and at a pressure of $120\,\text{kPa}$?

States of matter

Look at the four compounds listed below. 1. $(\text{CH}_3)_3\text{CH}$ 2. $\text{CH}_3\text{CH}_2\text{CH}_2\text{OH}$ 3. $\text{CH}_3\text{CH}_2\text{CH}_2\text{SH}$ 4. $\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_3$ In which sequence do their boiling points rise, starting with the lowest?

States of matter

Ethane may react with fluorine to form $1,2$-difluoroethane, $\text{C}_2\text{H}_4\text{F}_2$. $\text{C}_2\text{H}_6 + 2\text{F}_2 \rightarrow \text{C}_2\text{H}_4\text{F}_2 + 2\text{HF} \qquad \Delta H = -960\,\text{kJ mol}^{-1}$ Bond energies are provided. Calculate the bond energy of the $\text{C-F}$ bond in $1,2$-difluoroethane.

Chemical energetics

X is an impure sample of a Group 2 metal carbonate, $\text{MCO}_3$. In X, $57\%$ by mass is $\text{MCO}_3$. The impurities present in X do not react with hydrochloric acid. $7.4\,\text{g}$ of X is treated with an excess of dilute hydrochloric acid. $0.050\,\text{mol}$ of the Group 2 metal chloride is formed. What is the identity of the Group 2 metal?

Atoms, molecules and stoichiometry

At the very high temperatures inside car engines, nitrogen reacts with oxygen to form nitrogen monoxide. $\tfrac{1}{2}\text{N}_2(g) + \tfrac{1}{2}\text{O}_2(g) \rightarrow \text{NO}(g) \qquad \Delta H^{\circ} = +90\,\text{kJ mol}^{-1}$ The reaction has activation energy $E_a$. Which reaction profile diagram shows this reaction correctly?

Chemical energetics

For which reaction does chlorine’s oxidation number change by the greatest amount?

Electrochemistry

Hydrogen is manufactured on an industrial scale from methane, as represented by the equation below. $\text{CH}_4(g) + \text{H}_2\text{O}(g) \rightleftharpoons \text{CO}(g) + 3\text{H}_2(g) \qquad \Delta H^{\circ} = +205\,\text{kJ mol}^{-1}$ Which conditions produce the greatest yield of hydrogen at equilibrium?

Equilibria

$W$ moles of $\text{HNO}_2$ is subjected to a disproportionation reaction, giving $U$ moles of $\text{HNO}_3$ and $V$ moles of $\text{NO}$. No other product containing nitrogen is formed. Nitrogen is the only element that is oxidised or reduced. What are the values of $W$, $U$ and $V$?

Electrochemistry

On heating, gas $X$ undergoes dissociation to establish the equilibrium shown below. $X(g) \rightleftharpoons Y(g) + Z(g)$ A sample of gas $X$ is heated at constant pressure, $p$, at a particular temperature. It is then found that the equilibrium partial pressure of gas $X$ is $\tfrac{1}{7}p$. What is the equilibrium constant, $K_p$, at this temperature?

Equilibria

In the diagram, $X$ shows the Boltzmann distribution for the particle energies in a reaction, and $E_{a1}$ represents the activation energy for that reaction. Which statement is correct?

Reaction kinetics

Magnesium, aluminium and silicon are all elements in the Periodic Table. Each of these elements forms an oxide. Which row is correct?

The Periodic Table: chemical periodicity

Which statement gives the correct description of what occurs when silicon tetrachloride is added to water?

The Periodic Table: chemical periodicity

X and Y are two elements in Period 3 of the Periodic Table. Element X conducts electricity better than element Y. Element Y has a melting point that is higher than that of element X. Which formula is a compound made from element X and element Y?

The Periodic Table: chemical periodicity

A sample containing $1.0\,\text{mol}$ of anhydrous calcium nitrate is fully broken down by strong heating. How much gas is produced in total in this reaction?

Atoms, molecules and stoichiometry

Which gas sample below has the same atom count as $1\,\text{g}$ of hydrogen gas?

Atoms, molecules and stoichiometry

Steam is sent across heated magnesium to produce compound J and hydrogen. Which of the following is not a property of compound J?

Chemical bonding

Which statement is right?

Halogen compounds

$\text{ICl}$ forms when $\text{Cl}_2$ and $\text{I}_2$ react with each other. $\text{Cl}_2 + \text{I}_2 \rightleftharpoons 2\text{ICl}$ $\text{ICl}$ then reacts in water. $5\text{ICl} + 3\text{H}_2\text{O} \rightarrow 5\text{HCl} + \text{HIO}_3 + 2\text{I}_2$ Which row is right?

Group 17

$\text{NH}_4\text{Cl}$ reacts with $\text{NaOH}$ in aqueous solution. Which statement is correct?

Nitrogen and sulfur

What substance is formed when $60\,\text{g}$ of nitrogen monoxide reacts with an excess of carbon monoxide in a catalytic converter?

Atoms, molecules and stoichiometry

Which alkene exhibits geometric isomerism?

Hydrocarbons

What is the proper name for the main product formed when $\text{HBr}$ reacts with $3$-ethylhex-$3$-ene?

Hydrocarbons

The alkane $\text{CH}_3\text{CH}_2\text{CH}(\text{CH}_3)_2$ reacts with chlorine by free radical substitution. In this reaction, no $\text{C-C}$ bonds are broken. How many isomeric products, counting positional and optical isomers, with molecular formula $\text{C}_5\text{H}_{11}\text{Cl}$ are possible?

Chemical bonding

What does the mechanism of the reaction between aqueous $\text{NaOH}$ and $1$-bromobutane involve?

Chemical bonding

But-$2$-ene undergoes reaction with cold, dilute acidified $\text{KMnO}_4$ to form product X. But-$2$-ene reacts with an excess of hot, concentrated acidified $\text{KMnO}_4$ to form product Y. Which statement concerning X and Y is correct?

Hydrocarbons

How many protons, neutrons and electrons are there altogether in an ammonium ion with a relative formula mass of $21$?

Atomic structure

On heating with $\text{KOH}$ dissolved in ethanol, halogenoalkanes may undergo elimination, producing alkenes. What elimination products are possible if $2$-bromobutane is heated with $\text{KOH}$ dissolved in ethanol?

Halogen compounds

Chloroethane may be converted into sodium propanoate. $\text{chloroethane} \rightarrow \text{intermediate Q} \rightarrow \text{sodium propanoate}$ Intermediate Q is then hydrolysed using boiling aqueous $\text{NaOH}$ to form sodium propanoate. Which reagent would be used to prepare intermediate Q from chloroethane?

Halogen compounds

Four distinct alcohols are reacted with alkaline $\text{I}_2(\text{aq})$. Which row gives the correct answer?

Hydroxy compounds

The $M_r$ value of compound X is 88. Compound X is warmed under reflux with excess acidified potassium dichromate(VI) to form compound Y. Under suitable conditions, compound Y reacts with compound X to give compound Z. The $M_r$ value of compound Z is 172. Identify compound X.

Carboxylic acids and derivatives

Butanedione, $\text{CH}_3\text{COCOCH}_3$, is a yellow liquid. How does butanedione react with 2,4-dinitrophenylhydrazine reagent and Fehling’s reagent?

Carbonyl compounds

Which substance, on reacting with ethanoic acid, forms the organic product with the largest $M_r$?

Carboxylic acids and derivatives

A sample of propyl ethanoate is hydrolysed by being heated under reflux with aqueous NaOH. The two organic products formed in the hydrolysis are then separated, purified and weighed. What percentage by mass does each product make up of the total mass of products obtained?

Atoms, molecules and stoichiometry

Which statement about PVC is true?

Chemical bonding

Compound Q undergoes reaction separately with HCN and $\text{NaBH}_4$ under suitable conditions. In each case, an organic product containing a chiral centre is formed. What is compound Q?

Carbonyl compounds

Compound X shows the following characteristics. • If $0.20\,\text{mol}$ of X is completely burned, $14.4\,\text{dm}^3$ of carbon dioxide is formed, with the measurement taken under room conditions. • X reacts with 2,4-dinitrophenylhydrazine reagent to produce an orange crystalline product. • X does not form a yellow precipitate with alkaline $\text{I}_2\text{(aq)}$. What substance could X be?

Atoms, molecules and stoichiometry

This question concerns the first ionisation energies of magnesium and neon. Which row is correct?

The Periodic Table: chemical periodicity

A specimen of but-2-enoic acid, $\text{CH}_3\text{CH=CHCOOH}$, is examined by infrared spectroscopy. In the infrared spectrum, there is a broad absorption in the $2500$-$3000\,\text{cm}^{-1}$ interval. Which bond gives rise to this peak?

Chemical bonding

Arsenic is able to combine with fluorine to make a compound. In this species, the arsenic atom has no lone pair of electrons, and no dative bonds are present. Selenium is also able to combine with fluorine to make a compound. In this species, the selenium atom has no lone pair of electrons, and no dative bonds are present. Which of the compounds have two different bond angles? (For this question, ignore bond angles of $180^\circ$.)

Chemical bonding

The diagram shows a structure of borazole, $\text{N}_3\text{B}_3\text{H}_6$. What is the shape of borazole, and how many $\pi$ electrons does the structure contain?

Chemical bonding

The diagram illustrates the apparatus used to determine the relative molecular mass of a volatile liquid. When $0.10\,\text{g}$ of a volatile liquid is placed in the syringe, the whole sample vaporises and the volume rises by $85\,\text{cm}^3$. The heater keeps the temperature at $400\,\text{K}$, and the investigation is performed at a pressure of $101\,300\,\text{Pa}$. If the vapour of the volatile liquid acts as an ideal gas, which expression should be used to calculate the relative molecular mass of the liquid?

Atoms, molecules and stoichiometry

The table presents the physical properties of four substances, W, X, Y and Z. What are the identities of W, X, Y and Z?

Chemical bonding

The setup shown is used to work out a value for the enthalpy of combustion of butan-1-ol. The mass of $1.00\,\text{cm}^3$ of water is $1.00\,\text{g}$. Before heating, the mass of burner $+$ butan-1-ol is $58.34\,\text{g}$, and after heating it is $57.85\,\text{g}$. The water starts at $17.6\,^{\circ}\text{C}$ and finishes at $41.1\,^{\circ}\text{C}$. Butan-1-ol has $M_r = 74$. Using these data, what value, to three significant figures, can be found for the enthalpy of combustion of butan-1-ol?

Chemical energetics