AQA A Level Chemistry Paper 1 June 2019 question paper 7405/1

Figure 1 shows an incomplete Born–Haber cycle for the formation of caesium iodide. The diagram is not to scale.

Figure 1

Table 1 gives values of some standard enthalpy changes.

Complete Figure 1 by writing the formulas, including state symbols, of the appropriate species on each of the two blank lines.

Use Figure 1 and the data in Table 1 to calculate the standard enthalpy of atomisation of iodine.

The enthalpy of lattice formation for caesium iodide in Table 1 is a value obtained by experiment. The value obtained by calculation using the perfect ionic model is –582 kJmol^–1

Deduce what these values indicate about the bonding in caesium iodide.

Use data from Table 2 to show that this reaction is not feasible at 298 K

Time of flight (TOF) mass spectrometry can be used to analyse large molecules such as the pentapeptide, leucine encephalin (P).

P is ionised by electrospray ionisation and its mass spectrum is shown in Figure 2.

Describe the process of electrospray ionisation.

Give an equation to represent the ionisation of P in this process.

Equation

What is the relative molecular mass of P ? Tick (✓) one box.

A molecule Q is ionised by electron impact in a TOF mass spectrometer. The Q⁺ ion has a kinetic energy of 2.09 x 10^–15 J This ion takes 1.23 x 10^–5 s to reach the detector. The length of the flight tube is 1.50 m

Calculate the relative molecular mass of Q.

KE = mv² where m = mass (kg) and v = speed (m s^–1) The Avogadro constant, L = 6.022 x 10²³ mol^–1

Relative molecular mass

This question is about periodicity, the Period 4 elements and their compounds.

State the meaning of the term periodicity.

Identify the element in Period 4 with the highest electronegativity value.

Identify the element in Period 4 with the largest atomic radius. Explain your answer.

The equations for two reactions of arsenic(III) oxide are shown.

Name the property of arsenic(III) oxide that describes its ability to react in these two

Complete the equation for the formation of arsenic hydride.

Figure 3 shows some reactions of aqueous iron ions.

Give the formula of Precipitate J and state its colour. Give an equation for Reaction 1.

Equation

Give the formula of L and an equation for Reaction 2.

Equation

Suggest a reagent for Reaction 3.

Give the formula of Precipitate M and state its colour.

Transition metal complexes have different shapes and many show isomerism.

Describe the different shapes of complexes and show how they lead to different types of isomerism. Use examples of complexes of cobalt(II) and platinum(II).

You should draw the structures of the examples chosen.

This question is about some Group 7 compounds.

Solid sodium chloride reacts with concentrated sulfuric acid.

Give an equation for this reaction. State the role of the sulfuric acid in this reaction.

Equation

Fumes of sulfur dioxide are formed when sodium bromide reacts with concentrated sulfuric acid.

For this reaction

• give an equation

• give one other observation

• state the role of the sulfuric acid.

Equation

Chlorine reacts with hot aqueous sodium hydroxide as shown in the equation.

3Cl₂ + 6NaOH → NaClO₃ + 5NaCl + 3H₂O

Give the oxidation state of chlorine in NaClO₃ and in NaCl

State, in terms of redox, what happens to chlorine in the reaction in Question 05.3.

Solution Y contains two different negative ions.

To a sample of solution Y in a test tube a student adds

• silver nitrate solution

• then an excess of dilute nitric acid

• finally an excess of concentrated ammonia solution.

The observations after each addition are recorded in Table 3.

Give an equation to show the conversion of D into G.

Ionic equation to form E

Equation to show the conversion of D into G

A student does an experiment to determine the percentage of copper in an alloy.

The student

• reacts 985 mg of the alloy with concentrated nitric acid to form a solution (all of the copper in the alloy reacts to form aqueous copper(II) ions)

• pours the solution into a volumetric flask and makes the volume up to 250 cm³ with distilled water

• shakes the flask thoroughly

• transfers 25.0 cm³ of the solution into a conical flask and adds an excess of potassium iodide

• uses exactly 9.00 cm³ of 0.0800 mol dm^–3 sodium thiosulfate (Na₂S₂O₃) solution to react with all the iodine produced.

The equations for the reactions are

Calculate the percentage of copper by mass in the alloy.

Give your answer to the appropriate number of significant figures.

Suggest two ways that the student could reduce the percentage uncertainty in the measurement of the volume of sodium thiosulfate solution, using the same apparatus as this experiment.

State the role of iodine in the reaction with sodium thiosulfate.

Give the full electron configuration of a copper(II) ion.

Copper(I) iodide is a white solid.

Explain why copper(I) iodide is white.

Iodine vaporises easily.

Calculate the volume, in cm³, that 5.00 g of iodine vapour occupies at 185 °C and 100 kPa

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

Give your answer to 3 significant figures.

Sulfur trioxide decomposes on heating to form an equilibrium mixture containing sulfur dioxide and oxygen.

A sample of sulfur trioxide was heated and allowed to reach equilibrium at a given temperature. The equilibrium mixture contained 6.08 g of sulfur dioxide.

Calculate the mass, in g, of oxygen gas in the equilibrium mixture.

A different mass of sulfur trioxide was heated and allowed to reach equilibrium at 1050 K

The amounts of each substance in the equilibrium mixture are shown in Table 4.

For this reaction at 1050 K the equilibrium constant, K_p = 7.62 x 10⁵ Pa

Calculate the mole fraction of each substance at equilibrium. Give the expression for the equilibrium constant, K_p Calculate the total pressure, in Pa, of this equilibrium mixture.

K_p

For this reaction at 1050 K the equilibrium constant, K_p = 7.62 x 10⁵ Pa For this reaction at 500 K the equilibrium constant, K_p = 3.94 x 10⁴ Pa

Explain how this information can be used to deduce that the forward reaction is endothermic.

Use data from Question 07.3 to calculate the value of K_p, at 500 K, for the equilibrium represented by this equation.

This question is about structure and bonding.

Draw a diagram to show the strongest type of interaction between two molecules of ethanol (C₂H₅OH) in the liquid phase.

Include all lone pairs and partial charges in your diagram.

Methoxymethane (CH₃OCH₃) is an isomer of ethanol.

Table 5 shows the boiling points of ethanol and methoxymethane.

In terms of the intermolecular forces involved, explain the difference in boiling points.

Draw the shape of the POCl₃ molecule and the shape of the ClF₄^– ion. Include any lone pairs of electrons that influence the shapes.

In a POCl₃ molecule the oxygen atom is attached to the phosphorus atom by a double bond that uses two electrons from phosphorus.

Name each shape.

Suggest a value for the bond angle in ClF₄ ̄

Shape of POCl₃ Shape of ClF₄ ̄

Name of shape of POCl₃

Name of shape of ClF₄ ̄

Bond angle in ClF₄ ̄ 11

This question is about different pH values.

For pure water at 40 °C, pH = 6.67 A student thought that the water was acidic.

Explain why the student was incorrect.

Determine the value of K_w at this temperature.

Sodium hydroxide solution was added gradually from a burette to 25 cm³ of 0.080 mol dm^–3 propanoic acid at 25 °C The pH was measured and recorded at regular intervals.

The results are shown in Figure 4.

Use Figure 4 to determine the value of K_a for propanoic acid at 25 °C

Show your working.

Suggest which indicator is the most appropriate for the reaction in Question 09.2 ? Tick (✓) one box.

Indicator	pH range	Tick () one box
methyl orange	3.1 – 4.4
bromothymol blue	6.0 – 7.6
cresolphthalein	8.2 – 9.8
indigo carmine	11.6 – 13.0

A student prepared a buffer solution by adding 0.0136 mol of a salt KX to 100 cm³ of a 0.500 mol dm^–3 solution of a weak acid HX and mixing thoroughly.

The student then added 3.00 × 10^–4 mol of potassium hydroxide to the buffer solution.

Calculate the pH of the buffer solution after adding the potassium hydroxide.

For the weak acid HX at 25 °C the value of the acid dissociation constant,

Give your answer to two decimal places.

A buffer solution has a constant pH even when diluted.

Use a mathematical expression to explain this.