OCR A Level Chemistry A Periodic table, elements and physical chemistry June 2024 question paper H432/01

Oxygen has the electron configuration 1s²2s²2p⁴.

How are the electrons in an atom of oxygen arranged in the p-orbitals?

Your answer

Water has the anomalous properties below.

• Water has relatively high melting and boiling points.

• Ice is less dense than water.

Which statement explains these anomalous properties?

A The covalent bonding within water molecules.

B The hydrogen bonding between water molecules.

C The induced dipole–dipole interactions (London forces) between water molecules.

D The ionic bonding between water molecules.

Your answer

Which chemical process is the most sustainable in terms of the atom economy of the iron produced?

Your answer

Which compounds of magnesium can be used as ‘antacids’?

A Chlorides

B Hydroxides

C Nitrates

D Sulfates

Your answer

Which statement explains the trend in boiling points down the halogens group?

A The bond enthalpy of the covalent bonds increases.

B The halogens become less electronegative.

C The induced dipole–dipole interactions (London forces) become stronger.

D The reactivity of the halogens decreases.

Your answer

Which equation does not represent a disproportionation reaction?

Your answer

The equation for the reaction of sulfuric acid with potassium hydroxide is shown below.

25 cm³ of 1.00 mol dm^–3 H₂SO₄ is reacted with excess KOH. The energy given out is 2.8 kJ.

What is the enthalpy change of neutralisation, in kJ mol^–1?

A –56

B –70

C –112

D –224

Your answer

Which row in the table explains how a catalyst affects the activation energy (E_a) and the proportion of molecules with energy > E_a?

Your answer

A graph of ln(k) is plotted against 1 / T for a reaction. (k = rate constant, T = temperature in K.)

The gradient has the numerical value of –16 000.

What is the activation energy, in kJ mol^–1, for this reaction?

A +1.92

B +133

C +1920

D +133 000

Your answer

A reaction is zero order with respect to a reactant.

Which rate–concentration graph for the reactant is the correct shape?

Your answer

The reversible reaction between hydrogen and iodine to form hydrogen iodide is

The graph shows how the concentrations of the reactants and product change as the reaction reaches a dynamic equilibrium.

At which point on the graph is the equilibrium reached?

Your answer

Which solution can be added to CH₃COOH(aq) to make a buffer solution?

A CH₃COONa(aq)

B HCOOH(aq)

C HC l (aq)

D NaC l (aq)

Your answer

A student analyses a solution of a salt.

The results are shown below.

What is the formula of the salt?

A CuCl₂

B CuSO₄

C FeCl₂

D FeSO₄

Your answer

Chlorine has the electron configuration [Ne]3s²3p⁵.

Which statement(s) about chlorine is/are correct when it reacts in redox reactions?

1 It can gain one electron to form 1– ions.

2 It can lose its 3s² electrons to form 2+ ions.

3 It can lose its 3p⁵ electrons to form 5+ ions.

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

Which statement(s) about elements in the periodic table is/are correct?

1 The position of an element is determined by its relative atomic mass.

2 The elements in a group have similar chemical properties.

3 Transition elements are used as catalysts in the manufacture of chemicals.

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

This question is about energy changes.

Hydrogen peroxide decomposes as shown in Reaction 16.1.

The table shows enthalpy changes of formation and entropies.

	Hf / kJ mol–1	S / J K–1 mol–1
H2O2(l)	–188	110
H2O(l)	–286	70.0
O2(g)	0	205

Calculate the free-energy change, G, in kJ mol^–1, of Reaction 16.1 at 25 C.

Give your answer to 3 significant figures.

G =........ kJ mol^–1

The decomposition of hydrogen peroxide shown in Reaction 16.1 is feasible.

Suggest why Reaction 16.1 does not take place at 25 C despite being feasible.

The rate of decomposition of hydrogen peroxide shown in Reaction 16.1 can be increased by adding a small amount of powdered manganese(IV) oxide, MnO₂.

The MnO₂ acts as a catalyst.

Complete the enthalpy profile diagram for Reaction 16.1 using formulae for the reactants and products.

• Use E_a to label the activation energy without MnO₂.

• Use E_c to label the activation energy with MnO₂.

• Use H to label the enthalpy change of reaction.

Explain why MnO₂ is described as a heterogeneous catalyst for this reaction.

Mn₃O₄ is a compound in which Mn has two different oxidation states. The two oxidation states are different from the Mn in MnO₂.

Suggest the two oxidation states of manganese in Mn₃O₄.

Define the term lattice enthalpy.

Calculate the lattice enthalpy of MnO.

lattice enthalpy =........ kJ mol^–1

Using collision theory, explain why the gradient decreases over time.

* Use the graph to determine the order of reaction with respect to CV, the rate of the reaction at three minutes and the rate constant, k.

Your answer must show full working on the graph and on the lines below.

This question is about two oxides of sulfur: sulfur dioxide, SO₂, and sulfur trioxide, SO₃.

SO₃ decomposes to form SO₂ and O₂, as shown in Equilibrium 18.1.

2.25 moles of SO₃ is heated to 550 C in the presence of a catalyst and the resulting mixture allowed to reach equilibrium.

The equilibrium mixture contains 0.900 mol of SO₂ and the total pressure is 2.80 atm.

Calculate the numerical value for K_p for Equilibrium 18.1 under these conditions and state the units of K_p.

Give your answer to 3 significant figures.

The numerical values of K_p for Equilibrium 18.1 at temperatures T₁ and T₂ are shown below.

Explain why T₂ is a higher temperature than T₁.

Suggest how the value of K_p would change if the reaction was repeated with no catalyst added and the pressure of the system increased.

Tick (✓) one box in each row.

SO₂ and SO₃ both have molecules with sulfur in the centre and bond angles of approximately 120.

Explain why the bond angles in SO₃ are 120.

Explain why both SO₂ and SO₃ have polar bonds, but only SO₂ has polar molecules.

This question is about acids and bases.

Chloroethanoic acid, Cl CH₂COOH, is a weak monobasic acid.

Write the expression for the acid dissociation constant, K_a, of Cl CH₂COOH.

The expression for the acid dissociation constant, K_a, of Cl CH₂COOH can be simplified to:

State one approximation that allows the expression from (a)(i) to be simplified to Expression 19.1.

A student carries out an experiment to determine the pK_a value of a solution of Cl CH₂COOH.

• The concentration of Cl CH₂COOH is 0.090 mol dm^–3.

• The pH of Cl CH₂COOH is 1.95.

Use Expression 19.1 to calculate the pK_a value of Cl CH₂COOH.

Give your answer to 2 decimal places.

Draw a best-fit curve on the graph and calculate the concentration of the CH₃COOH solution.

CH₃COOH concentration =........ mol dm^–3

The end point of the titration can also be found by observing the colour change of an indicator.

The pH ranges of some indicators are shown in the table.

Identify the indicator in the table that would be suitable to observe the end point of the titration between CH₃COOH and Ba(OH)₂.

This question is about elements in the periodic table.

Chlorine has many uses.

Chlorine is used to treat water in large-scale water treatment plants.

Suggest why chlorine is added to water in large-scale water treatment plants.

Sea water contains aqueous bromide ions.

Chlorine is used to extract bromine from sea water.

Construct the ionic equation for this reaction and explain why chlorine is suitable for this extraction of bromine but iodine is not.

Equation........

Explanation........

Fluorine, F₂, reacts with nitrogen dioxide, NO₂, to form nitryl fluoride, NO₂F, as shown in Reaction 20.1 below.

The mechanism for this reaction involves two steps. Step 1 is the ‘slow’ step and Step 2 is the ‘fast’ step.

The equation for Step 2 is shown below:

Suggest the equation for Step 1 and the rate equation for Reaction 20.1.

Equation for Step 1:........

Rate equation for Reaction 20.1:........

* The table shows the melting points of some of the elements in Period 3 of the periodic table.

Element	Al	Si	P4	S8
Melting point / C	660	1410	44	119

Explain the melting points in terms of bonding and structure.

This question is about redox reactions and electrode potentials.

The flowchart shows some reactions of barium and its compounds.

• Write balanced equations for Reaction 1 and Reaction 2.

• Identify the type of reaction in Reaction 3.

Reaction 1: equation........

Reaction 2: equation........

Reaction 3: type of reaction........

Potassium iodate tablets prevent the uptake of radioactive iodine in the human body following a nuclear accident.

The mass of potassium iodate(V), KIO₃, in a tablet can be determined by reaction with an aqueous solution of potassium iodide, K I, in the presence of acid.

A chemist finds that two KIO₃ tablets react with exactly 26.2 cm³ 0.150 mol dm^–3 KI.

Calculate the mass, in mg, of KIO₃ in one tablet.

Give your answer to the nearest whole number.

Standard electrode potentials are measured by comparison with a reference half-cell.

Draw a labelled diagram to show how the standard electrode potential could be measured for the redox system below.

Include details of the apparatus, solutions and the standard conditions needed when measuring this standard electrode potential.

Standard conditions........

Many electric vehicles are powered by lithium-ion cells.

Hydrogen-oxygen fuel cells can also be used to power vehicles.

Six redox systems are shown in the table. State symbols have been omitted.

Redox system	Half-equation	E / V
1	Li+ + e– Li	–3.04
2	2H2O + 2e– H2 + 2OH–	–0.83
3	2H+ + 2e– H2	0.00
4	O2 + 2H2O + 4e– 4OH–	+0.40
5	Li+ + CoO2 + e– LiCoO2	+1.16
6	O2 + 4H+ + 4e– 2H2O	+1.23

A lithium-ion cell involves redox systems 1 and 5.

Construct the overall cell equation for a lithium-ion cell.

Hydrogen-oxygen fuel cells can operate in acidic or in alkaline conditions.

Show that for acidic and alkaline hydrogen–oxygen fuel cells, the standard cell potentials, and the overall cell equations, are the same.

Acidic........

Alkaline........

This question is about transition elements.

Suggest the formulae of A, B and C.

Complex ion A:........

Solid B:........

Complex ion C:........

Cobalt (III) forms an octahedral complex ion D, which contains both ammonia and chloride ligands.

Complex ion D has a molar mass of 197.9 g mol^–1.

Determine the formula and charge of complex ion D.

Red blood cells contain haemoglobin which transports oxygen around the body.

For efficient transportation of oxygen, healthy human blood must be maintained at a pH value between 7.35 and 7.45.

Human blood acts as a buffer due to the presence of carbonic acid, H₂CO₃, and hydrogencarbonate, HCO₃^–, ions as shown below.

• Explain, using ligand substitution, how haemoglobin transports oxygen around the body.

• Determine whether a sample of blood with a [HCO₃^–]: [H₂CO₃] ratio of 8.5:1 is healthy.