AQA A Level Chemistry Paper 3 June 2022 question paper 7405/3

A value for enthalpy of solution can be determined in two ways:

• from a cycle, using lattice enthalpy and enthalpies of hydration

• from the results of a calorimetry experiment.

Define the term enthalpy of lattice dissociation.

The enthalpy of solution for ammonium nitrate is the enthalpy change for the reaction shown.

Draw a suitably labelled cycle and use it, with data from Table 1, to calculate the enthalpy of lattice dissociation for ammonium nitrate.

A student does an experiment to determine a value for the enthalpy of solution for ammonium nitrate.

The student uses this method.

• Measure 25.0 cm³ of distilled water in a measuring cylinder.

• Pour the water into a beaker.

• Record the temperature of the water in the beaker.

• Add 4.00 g of solid NH₄NO₃ to the water in the beaker.

• Stir the solution and record the lowest temperature reached.

Table 2 shows the student’s results.

Calculate the enthalpy of solution, in kJ mol¹, for ammonium nitrate in this experiment.

Assume that the specific heat capacity of the solution, c = 4.18 J K¹ g¹

Assume that the density of the solution = 1.00 g cm³

The uncertainty in each of the temperature readings from the thermometer used in this experiment is ±0.1°C

Calculate the percentage uncertainty in the temperature change in this experiment.

Percentage uncertainty

Suggest a change to the student’s method, using the same apparatus, that would reduce the percentage uncertainty in the temperature change.

Give a reason for your answer.

Another student obtained a value of +15 kJ mol¹ using the same method.

Suggest the main reason for the difference between this experimental value for the enthalpy of solution and the correct value of +26 kJ mol¹

Table 3 shows some entropy data at 298 K

	Entropy S / J K1mol1
NH4NO3(s)	151
NH4(aq)	113
NO3(aq)	146

Calculate a value for the Gibbs free-energy change (G), at 298 K, for the reaction when ammonium nitrate dissolves in water.

Use data from Table 3 and the value of H from the equation. Assume for the solvent, water, that the entropy change, S = 0

Explain what the calculated value of G indicates about the feasibility of this reaction at 298 K

Ammonium nitrate decomposes as shown.

The entropy change (S) for this reaction is +144 J K^–1 mol¹

Calculate the temperature at which this reaction becomes feasible.

Tschermigite is a hydrated, water-soluble mineral, with relative formula mass of 453.2

The formula of tschermigite can be represented as M.xH₂O, where M represents all the ions present.

Table 4 shows its composition by mass.

In an analysis, it is found that the mineral contains the ions NH₄⁺, Al³⁺ and SO₄²

Calculate the empirical formula of tschermigite and the value of x in M.xH₂O

Describe the tests, with their results, including ionic equations, that would confirm the identities of the ions present.

Under suitable conditions, 2-bromobutane reacts with sodium hydroxide to produce a mixture of five products, A, B, C, D and E.

Products A, B and C are alkenes.

A is a structural isomer of B and C.

A does not exhibit stereoisomerism.

B and C are a pair of stereoisomers.

Products D and E are alcohols.

D and E are a pair of enantiomers.

Give the names of the two concurrent mechanisms responsible for the formation of the alkenes and the alcohols.

Mechanism to form alkenes

Mechanism to form alcohols

Define the term stereoisomers.

Deduce the name of isomer A.

Explain why A does not exhibit stereoisomerism.

Outline the mechanism for the reaction of 2-bromobutane with sodium hydroxide to form alkene A.

Deduce the name of isomer B and the name of isomer C.

Explain the origin of the stereoisomerism in B and C.

Draw 3D representations of enantiomers D and E to show how their structures are related.

A student compares the rates of hydrolysis of 1-chlorobutane, 1-bromobutane and 1-iodobutane.

The suggested method is:

• add equal volumes of the three halogenoalkanes to separate test tubes

• add equal volumes of aqueous silver nitrate to each test tube

• record the time taken for a precipitate to appear in each test tube.

State and explain the order in which precipitates appear.

Order in which precipitates appear

Hydrogen peroxide solution decomposes to form water and oxygen.

The reaction is catalysed by manganese(IV) oxide.

A student determines the order of this reaction with respect to hydrogen peroxide. The student uses a continuous monitoring method in the experiment.

The student places hydrogen peroxide solution in a conical flask with the catalyst and uses a gas syringe to collect the oxygen formed. The student records the volume of oxygen every 10 seconds for 100 seconds.

Explain why the reaction is fastest at the start.

The graph in Figure 1 shows how the concentration of hydrogen peroxide changes with time in this experiment.

Tangents to the curve in Figure 1 can be used to determine rates of reaction.

Draw a tangent to the curve when the concentration of hydrogen peroxide solution is

Use your tangent to calculate the gradient of the curve at this point.

The concentration of hydrogen peroxide solution at time t during the experiment can be calculated using this expression.

H₂O_2t = concentration of hydrogen peroxide solution at time t / mol dm_–3

H₂O_2initial = concentration of hydrogen peroxide solution at the start / mol dm_–3

V_max = total volume of oxygen gas collected during the whole experiment / cm³

V_t = volume of oxygen gas collected at time t / cm³

Use Figure 1 and the expression to calculate H₂O_2t when 20 cm₃ of oxygen has been collected.

Table 5 shows data from a similar experiment.

Plot the data from Table 5 on the grid in Figure 2.

Draw a line of best fit.

Use Figure 2 to determine the order of reaction with respect to H₂O₂

State how the graph shows this order.

How the graph shows this order

This question is about catalysis.

Zeolites are used as heterogeneous catalysts in the catalytic cracking of alkanes.

Tetradecane (C₁₄H₃₀) can be cracked to form octane and a cycloalkane.

Give an equation for this reaction.

State the meaning of the term heterogeneous.

Equation

A student determines the concentration of ethanedioate ions in an acidified solution by titration with potassium manganate(VII) solution.

The mixture is warmed before the addition of potassium manganate(VII) solution because the reaction is slow at first. When more potassium manganate(VII) solution is added, the mixture goes colourless quickly due to the presence of an autocatalyst.

Explain the meaning of the term autocatalyst.

Explain, using equations where appropriate, why the reaction is slow at first and then goes quickly.

The reaction between peroxodisulfate ions and iodide ions in aqueous solution can be

Table 6 gives relevant standard electrode potentials.

Use the electrode potential data to suggest how Co²⁺ catalyses the reaction.

Which atom in the ground state contains at least one unpaired p electron?

Complete combustion of 0.0100 mol of an organic acid produced 0.0200 mol of carbon dioxide.

The same amount of the acid required 20 cm³ of 1.00 mol dm^–3 NaOH (aq) for neutralisation.

Which could be the formula of the acid?

Which substance has no delocalised electrons?

Consider the change that occurs in the shape of the curve for the distribution of molecular energies in a gas when the temperature of the gas is increased.

Which is a correct statement about the gas molecules at a higher temperature?

Which of these oxidation states is correct?

Which change to a hydrogen electrode has no effect on the electrode potential?

Some electrode potential data are shown.

Which is a correct statement about this cell?

Which can not function as a Brønsted-Lowry acid?

A strong acid H₂X dissociates in aqueous solution.

What is the pH of a 0.020 mol dm^–3 solution of this acid?

Equal volumes of two solutions, each with the same concentration, are mixed together at 298 K

Which two solutions, when mixed, form a solution with a pH >7?

Which ionisation needs less energy than this process?

Which statement is correct about the Group 1 elements?

A test for chloride ions in aqueous solution involves adding dilute nitric acid followed by aqueous silver nitrate.

What is the reason for adding the nitric acid?

Which pair of reagents reacts to form a tetrahedral complex?

Cobalt(II) chloride solution changes colour when an excess of concentrated hydrochloric acid is added.

What type of reaction takes place?

The reaction between vanadium(IV) ions and manganate(VII) ions in acidic solution can be represented by the equation

What volume, in dm³, of 0.020 mol dm³ KMnO₄ is needed to oxidise 0.10 mol of vanadium(IV) ions completely?

2-Bromopropane reacts with bromine to form 2,2-dibromopropane.

What is the name of the mechanism of this reaction?

Which compound is formed from bromoethane in a nucleophilic substitution reaction?

Which statement is not correct for both primary and secondary alcohols?

Which compound is an isomer of ethyl ethanoate?

Which compound is an amide?

Suberoyl chloride, ClOC(CH₂)₆COCl, is commonly used in the manufacture of polymers.

Which compound can form a polymer with suberoyl chloride?

Which polymer is not hydrolysed when heated with aqueous alkali?

Which is the main species present in an aqueous solution of aspartic acid at pH = 14?

Which type of reaction is not involved in this reaction sequence?

Which pair of reagents does not produce ethanol?

Which type of interaction between polypeptide chains is mainly responsible for maintaining the secondary structure of a protein in the form of an alpha helix?

Which statement about HOCH₂CH(NH₂)COOH is correct?

Which compound can be dehydrated to form an alkene?

Which compound is not a 2-aminocarboxylic acid?