AQA A Level Chemistry Paper 1 June 2018 question paper 7405/1

This question is about lattice enthalpies.

Figure 1 shows a Born–Haber cycle for the formation of magnesium oxide.

Complete Figure 1 by writing the missing symbols on the appropriate energy levels.

Table 1 contains some thermodynamic data.

Calculate a value for the enthalpy of lattice formation for magnesium oxide.

Nitrogen and hydrogen were mixed in a 1:3 mole ratio and left to reach equilibrium in a flask at a temperature of 550 K. The equation for the reaction between nitrogen and hydrogen is shown.

When equilibrium was reached, the total pressure in the flask was 150 kPa and the mole fraction of NH₃(g) in the mixture was 0.80

Calculate the partial pressure of each gas in this equilibrium mixture.

Give an expression for the equilibrium constant (K_p) for this reaction.

In a different equilibrium mixture, under different conditions, the partial pressures of the gases are shown in Table 2.

Calculate the value of the equilibrium constant (K_p) for this reaction and give its units.

The enthalpy change for the reaction is –92 kJ mol^–1

State the effect, if any, of an increase in temperature on the value of K_p for this reaction. Justify your answer.

The equation for the reaction between ammonia and oxygen is shown.

Some standard entropies are given in Table 3.

Calculate the entropy change for the reaction between ammonia and oxygen.

Calculate a value for the Gibbs free-energy change (ΔG), in kJ mol^–1, for the reaction between ammonia and oxygen at 600 °C

(If you were unable to obtain an answer to Question 03.1, you should assume that the entropy change is 211 J K^–1 mol^–1. This is not the correct answer.)

The reaction between ammonia and oxygen was carried out at a higher temperature.

Explain how this change affects the value of Δ G for the reaction.

Platinum acts as a heterogeneous catalyst in the reaction between ammonia and oxygen. It provides an alternative reaction route with a lower activation energy.

Deduce the change in oxidation state of nitrogen, when NH₃ is oxidised to NO

When ammonia reacts with oxygen, nitrous oxide (N₂O) can be produced instead of NO

Give an equation for this reaction.

This question is about s-block metals.

Give the full electron configuration for the calcium ion, Ca²⁺

Explain why the second ionisation energy of calcium is lower than the second ionisation energy of potassium.

Identify the s-block metal that has the highest first ionisation energy.

Give the formula of the hydroxide of the element in Group 2, from Mg to Ba, that is least soluble in water.

A student added 6 cm³ of 0.25 mol dm^–3 barium chloride solution to 8 cm³ of 0.15 mol dm^–3 sodium sulfate solution. The student filtered off the precipitate and collected the filtrate.

Give an ionic equation for the formation of the precipitate. Show by calculation which reagent is in excess. Calculate the total volume of the other reagent which should be used by the student so that the filtrate contains only one solute.

Total volume of other reagent

A sample of strontium has a relative atomic mass of 87.7 and consists of three

State why the isotopes of strontium have identical chemical properties. Calculate the percentage abundance of the⁸⁸Sr isotope in this sample.

Why isotopes of strontium have identical chemical properties

A time of flight (TOF) mass spectrum was obtained for a sample of barium that

Identify the ion with the longest time of flight.

A¹³⁷Ba⁺ ion travels through the flight tube of a TOF mass spectrometer with a

The Avogadro constant, L = 6.022 × 10²³ mol^–1

Calculate the length of the flight tube in metres. Give your answer to the appropriate number of significant figures.

Hydrochloric acid is a strong acid and ethanoic acid is a weak acid.

State the meaning of the term strong acid.

In an experiment, 10.35 cm³ of 0.100 mol dm^–3 hydrochloric acid are added to 25.0 cm³ of 0.150 mol dm^–3 barium hydroxide solution.

Calculate the pH of the solution that forms at 30 °C

Give your answer to 2 decimal places.

The pH of water at 30 °C is 6.92

Give the reason why water is neutral at this temperature.

Identify the oxide that could react with water to form a solution with pH = 2

Tick (✓) one box.

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

A buffer solution contains 0.025 mol of sodium ethanoate dissolved in 500 cm³ of 0.0700 mol dm^–3 ethanoic acid at 25 °C A sample of 5.00 cm³ of 2.00 mol dm^–3 hydrochloric acid is added to this buffer solution.

Calculate the pH of the solution formed.

For ethanoic acid, K_a = 1.76 × 10^–5 mol dm^–3 at 25 °C

A student set up the cell shown in Figure 2.

The student recorded an initial voltage of +0.16 V at 25 °C

Explain how the salt bridge provides an electrical connection between the two solutions.

The standard electrode potential for the Cu²⁺/Cu electrode is

Calculate the electrode potential of the left-hand electrode in Figure 2.

Electrode potential
V

Both electrodes contain a strip of copper metal in a solution of aqueous Cu²⁺ ions.

State why the left-hand electrode does not have an electrode potential of +0.34 V

Give the conventional representation for the cell in Figure 2. Include all state symbols.

When the voltmeter is replaced by a bulb, the EMF of the cell in Figure 2 decreases over time to 0 V

Suggest how the concentration of copper(II) ions in the left-hand electrode changes when the bulb is alight. Give one reason why the EMF of the cell decreases to 0 V

Change in concentration of copper(II) ions in the left-hand electrode

Reason why the EMF decreases to 0 V

When anhydrous aluminium chloride reacts with water, solution Y is formed that contains a complex aluminium ion, Z, and chloride ions.

Give an equation for this reaction.

Give an equation to show how the complex ion Z can act as a Brønsted–Lowry acid with water.

Describe two observations you would make when an excess of sodium carbonate solution is added to solution Y. Give an equation for the reaction. In your equation, include the formula of each complex aluminium species.

Equation

Aqueous potassium hydroxide is added, until in excess, to solution Y.

Describe two observations you would make. For each observation give an equation for the reaction that occurs. In your equations, include the formula of each complex aluminium species.

Equation 1

Equation 2

This question is about sodium and some of its compounds.

Use your knowledge of structure and bonding to explain why sodium bromide has a melting point that is higher than that of sodium, and higher than that of sodium iodide.

When 250 mg of sodium were added to 500 cm³ of water at 25 °C a gas was produced.

Give an equation for the reaction that occurs. Calculate the volume, in cm³, of the gas formed at 101 kPa

The gas constant, R = 8.31 J K^–1 mol^–1

Calculate the concentration, in mol dm^–3, of sodium ions in the solution produced in the reaction in Question 08.2.

Sodium reacts with ammonia to form the compound NaNH₂ that contains the

Draw the shape of the NH₂^– ion. Include any lone pairs of electrons that influence the shape.

Predict the bond angle. Justify your prediction.

Shape

This question is about vanadium compounds and ions.

Use data from Table 4 to identify the species that can be used to reduce VO₂⁺ ions to VO²⁺ in aqueous solution and no further. Explain your answer.

Give the oxidation state of vanadium in [VO(H₂O)₅]²⁺

The [V(H₂O)₄Cl₂]⁺ ion exists as two isomers. One isomer is shown.

Draw the structure of the other isomer and state the type of isomerism.

Type of isomerism

Heating NH₄VO₃ produces vanadium(V) oxide, water and one other product.

Give an equation for the reaction.

Vanadium(V) oxide is the catalyst used in the manufacture of sulfur trioxide.

Give two equations to show how the catalyst is used and regenerated.

A student added 627 mg of hydrated sodium carbonate (Na₂CO₃.xH₂O) to 200 cm³ of 0.250 mol dm^–3 hydrochloric acid in a beaker and stirred the mixture. After the reaction was complete, the resulting solution was transferred to a volumetric flask, made up to 250 cm³ with deionised water and mixed thoroughly. Several 25.0 cm³ portions of the resulting solution were titrated with 0.150 mol dm^–3 aqueous sodium hydroxide. The mean titre was 26.60 cm³ of aqueous sodium hydroxide.

Show your working. Give your answer as an integer.