AQA A Level Chemistry Paper 1 June 2023 question paper 7405/1

This question is about complexes of the transition metal chromium.

State the meaning of the term transition metal complex.

Cr(PF₃)₆ is a complex of chromium that contains molecules of PF₃

The electron pair repulsion theory can be used to predict the shape of a PF₃ molecule.

Draw the shape of a PF₃ molecule. Include any lone pairs of electrons that influence the shape.

Name the shape.

Shape

Suggest why the oxidation state of chromium is zero in Cr(PF₃)₆

The compound [Cr(NH₃)₄Cl₂]Cl contains ammonia molecules.

Deduce the oxidation state of chromium in [Cr(NH₃)₄Cl₂]Cl

Name the type of bond between N and H in ammonia.

The compound [Cr(NH₃)₄Cl₂]Cl contains a complex ion that shows isomerism.

Draw the two isomers of the complex ion.

State the type of isomerism shown.

Isomer 1
Isomer 2

Type of isomerism

Complete the equation to show the formation of one complex that contains chromium in its +3 oxidation state.

Figure 1 shows a cell used to measure the standard electrode potential for the half-cell

State the purpose of the salt bridge.

Identify an ionic compound that could be used in the salt bridge.

State how, if at all, the EMF of this cell will change if the surface area of the platinum electrode is increased.

The standard electrode potential, for the half-cell is shown.

Water is added to the beaker containing the magnesium chloride solution.

What is the effect on the magnitude of the EMF of the cell?

Tick (✓) one box.

The voltmeter V shown in Figure 1 is replaced by a bulb.

Give an equation for the overall reaction that occurs when the cell is operating.

This question is about Period 3 elements and their oxides.

Give an equation for the reaction between phosphorus and an excess of oxygen.

Give an equation for the reaction between sulfur dioxide and water.

Give the displayed formula for the anion formed when sulfur trioxide reacts with water.

Give an equation for the reaction of magnesium with steam.

State one observation made.

Equation

Give an equation to show how an excess of magnesium oxide reacts with

Nitrogen dioxide decomposes at a high temperature.

A 0.317 mol sample of nitrogen dioxide is placed in a sealed flask and heated at a constant temperature until equilibrium is reached.

At equilibrium, the flask contains 0.120 mol of oxygen.

Calculate the mole fraction of each substance at equilibrium.

The total pressure in the flask in Question 04.1 is 120 kPa at equilibrium.

Calculate the partial pressure, in kPa, of NO₂

If you were unable to answer Question 04.1 you should assume that the mole fraction of NO₂ is 0.380. This is not the correct answer.

Table 1 shows the mole fractions of the three gases in a different equilibrium mixture.

For this equilibrium mixture, K_p = 59.7 kPa

Give an expression for K_p for this reaction.

Use your expression and the data in Table 1 to calculate the total pressure, in kPa, in the flask.

The equilibrium mixture in Question 04.3 is compressed into a smaller volume.

Deduce the effect, if any, of this change on the equilibrium yield of oxygen and on the

Effect on yield of oxygen

The equilibrium mixture in Question 04.3 is allowed to reach equilibrium at a lower temperature.

Explain why the equilibrium yield of oxygen decreases.

This question is about metal chlorides.

Table 2 shows some enthalpy change data.

Use the data in Table 2 to calculate the molar enthalpy change when calcium chloride dissolves in water.

Molar enthalpy change
kJ mol^–1

Use your answer to Question 05.1 to deduce how the temperature changes when calcium chloride dissolves in water.

Explain why the enthalpy of hydration of fluoride ions is more negative than the enthalpy of hydration of chloride ions.

Figure 2 shows an incomplete Born–Haber cycle for calcium chloride.

Complete the Born–Haber cycle by writing the formulas of the missing species on each of the two blank lines.

Table 3 shows some enthalpy change data.

Use Figure 2 and data from Table 3 to calculate the second ionisation energy of calcium.

Second ionisation energy
kJ mol^–1

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

Table 4 shows lattice enthalpies based on a perfect ionic model and lattice enthalpies from Born–Haber cycles for three metal chlorides.

Discuss the values in Table 4.

In your answer you should

compare the three values based on a perfect ionic model

compare the values based on a perfect ionic model to the values from a Born–Haber cycle for each compound.

The concentration of dilute hydrochloric acid can be found by titration using a standard solution of barium hydroxide.

Calculate the mass, in g, of solid barium hydroxide (M_r = 171.3) needed to prepare 250 cm³ of 0.100 mol dm^–3 barium hydroxide solution.

The mass of barium hydroxide from Question 06.1 is dissolved in a beaker containing

Describe how this solution is used to make 250 cm³ of the 0.100 mol dm^–3 barium hydroxide solution.

Before the first titration, the 25 cm³ pipette is rinsed with a small volume of the 0.100 mol dm^–3 barium hydroxide solution.

State why it is good practice to rinse the pipette in this way.

Hydrochloric acid is added to the burette using a funnel.

State why it is good practice to remove the funnel from the burette before the titration.

In a different experiment, 0.952 g of solid barium hydroxide is used to make 250 cm³ of standard barium hydroxide solution.

25.0 cm³ of this barium hydroxide solution reacts with exactly

Calculate the concentration of the hydrochloric acid.

The uncertainty in the 25.0 cm³ of solution from the pipette is ±0.05 cm³

The total uncertainty in the 24.50 cm³ of solution from the burette is ±0.15 cm³

Calculate the total percentage error in using the pipette and burette.

This question is about complexes containing the aluminium ion.

Give the electron configuration of the Al³⁺ ion.

When anhydrous aluminium sulfate, Al₂(SO₄)₃, is added to water a solution forms that contains the complex aluminium ion, [Al(H₂O)₆]³⁺

Give the equation for the reaction.

Explain why the solution containing [Al(H₂O)₆]³⁺ is acidic.

State why the concentration of aluminium sulfate solution can not be determined by

An excess of aqueous ammonia is added to a solution containing [Al(H₂O)₆]³⁺

Give an ionic equation for the reaction and state one observation.

Equation

An excess of dilute sulfuric acid is added to the products of the reaction in Question 07.5

Identify the aluminium species produced.

Figure 3 shows the structure of the EDTA^4– ion.

Atoms of two different elements in EDTA^4– can form co-ordinate bonds with an aluminium ion.

On Figure 3, draw circles around the atoms of two different elements that would link to an aluminium ion by a co-ordinate bond.

Hydrated aluminium sulfate, Al₂(SO₄)₃.xH₂O, is soluble in water.

The relative formula mass and value of x can be found from a titration experiment.

Aqueous [Al(H₂O)₆]³⁺ ions react to form a stable complex when treated with an excess

The excess of EDTA^4– ions is determined by titration with ZnSO₄ solution.

• Dissolve 1.036 g of Al₂(SO₄)₃.xH₂O in distilled water and make up to 250 cm³

• Add 25.0 cm³ of this solution to 50.0 cm³ of a solution containing EDTA^4– ions of concentration 0.0100 mol dm^–3

• Determine the excess of EDTA^4– ions by titrating with ZnSO₄ solution in the presence of an indicator.

The excess of EDTA^4– ions requires 18.00 cm³ of 0.0105 mol dm^–3 ZnSO₄ solution to

The equations for the reactions are

Use the information given to calculate the M_r of Al₂(SO₄)₃.xH₂O

Give your answer as an integer.

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This question is about fuel cells.

In a methanol–oxygen fuel cell, the overall reaction is

At the positive electrode, oxygen reacts with hydrogen ions to form water.

Give a half-equation for this reaction.

At the negative electrode, methanol reacts with water to produce carbon dioxide and hydrogen ions.

Give a half-equation for this reaction.

The standard electrode potential for the CO₂ / CH₃OH electrode is +0.03 V

Calculate the standard electrode potential for the O₂ / H₂O electrode.

State why a fuel cell does not need to be electrically recharged.

Suggest one advantage of using methanol, rather than hydrogen, in a fuel cell for use in cars.

This is a question about time of flight (TOF) mass spectrometry.

Give the equation, including state symbols, for the formation of Sr⁺ ions from Sr atoms by electron impact.

A sample of strontium is analysed by TOF mass spectrometry. The sample is ionised using electron impact.

The ions are accelerated to have a kinetic energy (KE) of 7.02 × 10^–20 J An ion takes 9.47 × 10^–4 s to travel along a 95.0 cm flight tube.

Use the information given to deduce the mass number of this ion.

The Avogadro constant, L = 6.022 × 10²³ mol⁻¹

Explain how the ions are detected in the TOF mass spectrometer.

State how the relative abundance of the ions is determined.

How ions are detected

How relative abundance is determined

A sample of strontium contains three isotopes,⁸⁶Sr,⁸⁷Sr and⁸⁸Sr

Calculate the percentage abundance of⁸⁷Sr in this sample.

Use your answer to deduce the relative atomic mass (A_r) of the sample. Give your answer to 1 decimal place.

Electrospray ionisation is used instead of electron impact for the ionisation of a protein in a mass spectrometry experiment.

Suggest why.

This question is about weak acids.

Table 5 shows the pH ranges of some indicators.

Identify the indicator that is most suitable for use in a titration between propanoic acid and sodium hydroxide.

Give the expression for the acid dissociation constant (K_a) for propanoic acid

Calculate the pH of a 0.100 mol dm^–3 propanoic acid solution. Give your answer to 2 decimal places.

For propanoic acid, pK_a = 4.87

For butanoic acid, K_a = 1.51 × 10^–5 mol dm^–3

20.0 cm³ of 0.100 mol dm^–3 sodium hydroxide solution are added to 25.0 cm³ of 0.100 mol dm^–3 butanoic acid solution.

Calculate the pH of the solution formed.

A student plans to titrate butanoic acid solution with a solution of ethylamine.

Explain why this titration could not be done using an indicator.