OCR A Level Chemistry A Periodic table, elements and physical chemistry June 2023 question paper H432/01

Which sample contains the greatest number of molecules?

A 35.0 g of C₂H₂

B 45.0 g of C₂H₆

C 60.0 g of C₄H₁₀

D 100.0 g of C₆H₆

Your answer

0.688 g of an oxide of manganese is reduced by hydrogen gas to form manganese metal and 0.235 g of water.

What is the formula of the oxide of manganese?

A MnO

B MnO₂

C Mn₂O₃

D Mn₃O₄

Your answer

How many hydrogen atoms are in 2.50 g of pharmacolite, CaHAsO₄•2H₂O (M_r = 216.0)?

A 6.97 10²¹

B 2.09 10²²

C 2.79 10²²

D 3.48 10²²

Your answer

40.0 cm³ of 0.200 mol dm^–3 HCl is added to 60.0 cm³ of 0.100 mol dm^–3 NaOH.

What is the concentration of the resulting solution?

A 0.0200 mol dm^–3 HCl and 0.0200 mol dm^–3 NaCl

B 0.0200 mol dm^–3 HCl and 0.0400 mol dm^–3 NaCl

C 0.0200 mol dm^–3 HCl and 0.0600 mol dm^–3 NaCl

D 0.0600 mol dm^–3 HCl and 0.0200 mol dm^–3 NaCl

Your answer

Which compound has polar molecules?

A HCN

B BCl₃

C CO₂

D C₂F₄

Your answer

Which element has the largest third ionisation energy?

Your answer

The reaction below is first order with respect to reactant X.

When the initial concentration of X is 1.0 mol dm^–3, the half-life is 16 minutes.

What is the half-life when the initial concentration of X is 2.0 mol dm^–3?

A 2 minutes

B 4 minutes

C 8 minutes

D 16 minutes

Your answer

Which compound requires the most energy to convert one mole into its gaseous ions?

A NaF

B Na₂O

C MgF₂

D MgO

Your answer

What is the percentage dissociation of a 0.015 mol dm^–3 solution of methanoic acid, HCOOH (K_a = 1.60 10^–4 mol dm^–3)?

A 0.016%

B 1.1%

C 1.82%

D 10.3%

Your answer

A student adds aqueous potassium carbonate to one test tube and aqueous silver nitrate to a second test tube.

The student adds dilute hydrochloric acid to each test tube.

Which row has the correct observations?

Your answer

The equations show the electrode potentials of the half-cells used in a lithium-ion cell.

Which statement is correct in a lithium-ion cell?

A The cell potential is 2.88 V.

B The reaction at the positive electrode is: LiCoO₂ Li⁺ + CoO₂ + e^–

C The overall cell reaction is: Li + CoO₂ LiCoO₂

D The oxidation number of Co changes from +2 to +1.

Your answer

Which substance(s) has/have induced dipole–dipole interactions (London forces) in the solid state?

1 C₂H₆

2 H₂O

3 Si

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

Which statement(s) is/are correct for the anti-cancer complex Pt(NH₃)₂Cl₂?

1 It has bond angles of 90º.

2 The oxidation number of Pt is +4.

3 It forms both optical and cis-trans isomers.

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.

Lattice enthalpies can be determined indirectly using Born-Haber cycles.

The table below shows the energy changes that are needed to determine the lattice enthalpy of barium iodide, BaI₂.

The diagram below shows an incomplete Born-Haber cycle that can be used to calculate the lattice enthalpy of barium iodide.

On the dotted lines, add the species present, including state symbols.

Ba²⁺(g) + 2I(g) + 2e^–

Calculate the lattice enthalpy of barium iodide.

lattice enthalpy =........ kJ mol^–1

The first and second ionisation energies of magnesium, Mg, and strontium, Sr, in Group 2 are given in the table below.

• Explain why the first ionisation energy of Mg is greater than the first ionisation energy of Sr.

• Explain why the second ionisation energy of Sr is greater than the first ionisation energy of Sr.

This question is about enthalpy changes of reactions involving hydrocarbons.

A student determines the enthalpy change of combustion, _cH, of heptane, C₇H₁₆, using the method outlined below.

• Add 150 g of water to a beaker and measure its temperature.

• Weigh a spirit burner containing heptane and use it to heat the water.

• Extinguish the flame and record the maximum temperature reached by the water.

• Reweigh the spirit burner.

The temperature of the water increased by 10.5 °C.

The spirit burner decreased in mass by 0.133 g.

Use the student’s results to determine the enthalpy change of combustion of heptane, _cH (C₇H₁₆), in kJ mol^–1.

_cH (C₇H₁₆) =........ kJ mol^–1

Nonane, C₉H₂₀, can be broken down by heat to form pentane, C₅H₁₂, and ethene, C₂H₄.

The enthalpy changes of combustion of C₉H₂₀(g) and C₂H₄(g) are shown in the table below.

Use H in Reaction 1 and the enthalpy changes of combustion in the table to determine the enthalpy change of combustion of C₅H₁₂(g).

∆_cH (C₅H₁₂(g)) =........ kJ mol^–1

Ethene can be produced from ethanol, as shown in Reaction 2 below.

Predict the sign of the entropy change, S, for Reaction 2.

Explain your reasoning.

This question is about oxides of nitrogen.

An investigation is carried out on the equilibrium system shown below.

A sealed flask containing 6.00 moles of NO₂(g) is heated to a constant temperature and allowed to reach equilibrium.

The equilibrium mixture contains 5.40 mol of NO₂(g), and the total pressure is 5.00 atm.

Determine the value of K_p and give your answer to 3 significant figures.

Include an expression for K_p and the units of K_p in your answer.

The sealed flask in (a)(i) is then heated to a higher temperature at an increased pressure. The system is allowed to reach equilibrium again.

Explain why it is difficult to predict how these changes in reaction conditions affect the amount of N₂O₄(g) formed at equilibrium.

N₂O₄ reacts fully with oxygen to form a different oxide of nitrogen, oxide A, as the only product.

Oxide A is collected and cooled to 75.0 °C at a pressure of 101 kPa.

Under these conditions, oxide A is a gas that occupies a volume of 74.0 cm³ and has a mass of 0.280 g.

Calculate the molar mass of oxide A and suggest its molecular formula.

molar mass =........ g mol

This question is about acids and bases.

Table 20.1 shows the ionic product, K_w, of water at 25 °C and 40 °C.

Table 20.1

Temperature /°C	Kw / mol2 dm–6
25	1.00 10−14
40	2.92 10−14

Calculate the pH of water at 40 °C.

Give your answer to 2 decimal places.

Table 20.1 shows different K_w values at 25 °C and at 40 °C. A student suggests that water is neutral at these temperatures.

Explain why this student is correct.

A student reacts strontium metal with water to make a 250.0 cm³ solution of aqueous strontium hydroxide, Sr(OH)₂. The solution contains 0.145 g of strontium hydroxide.

• Write an equation for the reaction of strontium with water.

• Calculate the pH of this 250.0 cm³ solution of strontium hydroxide at 40 °C. You should refer back to Table 20.1 at the start of (a).

Give your answer to 2 decimal places.

Equation........

Calculation

A student reacts 1.00 g of strontium carbonate, SrCO₃, with an excess of dilute nitric acid, HNO₃. A gas is produced.

Construct the equation for this reaction.

The student then reacts 1.00 g of calcium carbonate, CaCO₃, with an excess of dilute nitric acid, HNO₃.

Explain why the student’s two reactions produce different volumes of gas.

A student reacts an excess of magnesium with 25.0 cm³ of 0.500 mol dm^–3 hydrochloric acid, HC l.

The student also reacts an excess of magnesium with 25.0 cm³ of 0.500 mol dm^–3 ethanoic acid, CH₃COOH.

Construct an ionic equation for the reaction of magnesium with an acid.

Explain why these two reactions of magnesium produce the same volume of gas but at different rates.

Butanoic acid, CH₃CH₂CH₂COOH, is a weak monobasic acid.

Explain what is meant by the term monobasic acid.

A buffer solution is prepared by dissolving 3.39 g of potassium hydroxide in 250 cm³ of 0.376 mol dm^–3 butanoic acid.

This buffer solution has a pH of 5.07 at 25 °C.

Calculate the acid dissociation constant, K_a, of butanoic acid at 25 °C.

Assume that the volume of the solution remains constant at 250 cm³ when the potassium hydroxide is dissolved.

K_a =........ mol dm^–3

A buffer solution has a pH of 4.50.

When a small volume of water is added to this buffer solution, the pH does not change.

Explain why the pH does not change.

Some grass fertilisers contain compounds of iron.

During heavy rain, a fertiliser is washed into a nearby river causing the water to be polluted with a mixture of iron(II) and iron(III) ions.

A student determines the concentration of iron(II) ions in a sample of river water by titration with potassium manganate(VII).

25.0 cm³ portions of river water are acidified with dilute sulfuric acid. Each portion is titrated with 0.00250 mol dm –3 potassium manganate(VII) until a colour change is seen.

State the colour change seen at the end point of the titration.

The student’s titration results are shown in the table below. The trial titre has been omitted.

Complete the table above and calculate the mean titre that the student should use to determine the concentration of iron(II) ions in the river water.

Determine the concentration, in mol dm –3, of iron(II) ions in the river water.

concentration =........ mol dm^–3

This question is about the d-block elements in Period 4 of the periodic table (Sc to Zn).

* Explain, with examples from Period 4, what is meant by the terms d-block element and transition element.

Explain why some d-block elements are not transition elements.

Use electron configurations to support your explanations.

Describe precipitation reactions using either copper or chromium ions as examples.

Include equations.

Describe ligand substitution reactions using either copper or chromium ions as examples.

Include equations.

The ethanedioate ion, C₂O₄^2–, is a bidentate ligand.

A complex ion of cobalt(III) contains two ethanedioate ligands and two water ligands.

Determine the charge of this complex ion and the coordination number of cobalt in the complex ion.

Charge of complex ion........

Coordination number of cobalt........

An acidified solution containing Cr₂O₇^2– ions reacts with vanadium(III) ions in a redox reaction to form a solution containing Cr³⁺ ions and VO₂⁺ ions.

Construct the overall equation for this reaction.