AQA A Level Chemistry Paper 2 June 2023 question paper 7405/2

This question is about rates of reaction.

Figure 1 shows apparatus used to measure the rate of reaction when an acid reacts with an excess of solid sodium hydrogencarbonate, NaHCO₃

When different monoprotic organic acids are used, the rates at which gas escapes can be used to compare the strengths of the acids.

A timer is started when the NaHCO₃ is added to the acid and the mass of CO₂ gas lost is recorded at regular intervals. (It is assumed that any change in mass is due to the loss of CO₂)

Suggest a reason why using a conical flask instead of a beaker would give more accurate results in this experiment.

Figure 2 shows the results of this experiment when 25.0 cm³ of a 2.23 mol dm^–3 solution of ethanoic acid reacts with an excess of NaHCO₃

Use Figure 2 to calculate the rate of reaction at 2 minutes.

Deduce the units of your calculated rate.

Chloroethanoic acid is a stronger acid than ethanoic acid.

Sketch, on Figure 2, the curve you would expect when 25.0 cm³ of a 2.23 mol dm^–3 solution of chloroethanoic acid reacts with an excess of NaHCO₃

Suggest why chloroethanoic acid is a stronger acid than ethanoic acid.

A and B react together in the presence of an acid catalyst.

A(aq) + 2 B(aq) → C(aq) + D(aq)

The rate equation for this reaction is

Table 1 shows how the values of the relative initial rate vary with different concentrations of each reagent at the same temperature.

Complete Table 1 by calculating the missing values.

A suggested mechanism for the reaction is shown.

Deduce the rate-determining step for this reaction.

Give a reason for your answer.

Rate-determining step

This question is about intermediates in reaction mechanisms.

Figure 3 shows an intermediate formed in the first step of a nucleophilic addition–elimination mechanism.

Figure 3

Complete Figure 3 to show the structures of the two reactant species with curly arrows and relevant lone pairs of electrons involved in the formation of the intermediate.

Draw curly arrows and relevant lone pairs of electrons on the intermediate to show how the final products are formed.

Figure 4 shows an intermediate formed in the first step of a reaction mechanism of methylbenzene.

Complete Figure 4 to show the reactant species and any curly arrows involved in the formation of the intermediate.

Draw a curly arrow on the intermediate to show how the product is formed.

Give the name of the reaction mechanism.

Name of mechanism

Figure 5 shows the reactant species involved in the first step of a mechanism.

Figure 5

Complete Figure 5 to show the structure of the intermediate formed with curly arrows involved in its formation.

Give the name of the reaction mechanism.

Name of mechanism

Acrylonitrile, H₂C=CHCN, can be used as a starting material for the synthesis of butane-1,4-diamine, as shown in this reaction scheme.

Use IUPAC rules to name isomer W.

Reaction 1 produces a mixture of W and two other isomers.

Draw the structures of the two other isomers.

Explain, by considering the mechanism of this reaction, why all three isomers are formed.

The reaction scheme is repeated here.

Identify the reagent that is warmed with isomer W in reaction 2.

State the other reaction condition needed.

State the reagent and reaction conditions needed for reaction 3.

Give an equation for reaction 3.

Reagent and conditions

Equation

An incomplete equation for the formation of nylon 4,6 from five molecules of butane-1,4-diamine and five molecules of hexanedioic acid is shown.

Deduce the values of x and y in this equation.

Figure 6 shows a section of the nylon 4,6 polymer molecule.

Figure 6

Draw, on Figure 6, another section of nylon 4,6 polymer showing two hydrogen bonds between the two sections.

This question is about compound Z, with molecular formula C₇H₁₂O₃

Figure 7 shows the infrared spectrum of Z.

Identify the bond that causes the absorption at 1725 cm^–1

Figure 8 shows the¹³C NMR spectrum of Z.

How many different carbon environments are there in a molecule of Z ?

State the type of carbon environment that causes the peak at = 174 ppm

Use Table C in the Data Booklet to help you answer this question.

Table 2 shows data from the¹H NMR spectrum for compound Z.

Explain what can be deduced from the splitting patterns and chemical shift values for the peaks at = 4.10 ppm and at = 1.26 ppm

Deduce the part of the structure of Z that causes the peaks at

Use Table B in the Data Booklet to help you answer this question.

Peak at = 1.26 ppm

Part of structure

Deduce the part of the structure of Z that causes the peak at = 2.19 ppm

Part of structure

Figure 9 shows the¹H NMR spectrum of compound Z.

Suggest why it would be difficult to determine the structure of Z using the spectrum in Figure 9, without the information in Table 2 on page 13.

Deduce the structure of Z.

A student plans a series of chemical tests to confirm the identities of four organic

This is the student’s method.

To separate test tubes containing samples of each liquid:

Test 1 add potassium dichromate(VI) solution and warm gently

Test 2 add Fehling’s solution and cool in iced water

Test 3 add sodium hydrogencarbonate solution and test any gas produced with a lighted splint

Test 4 add bromine water and shake at room temperature.

Identify the missing reagent needed in Test 1.

In addition to the missing reagent in Test 1, there is a mistake in the method for two of the other tests.

State the two mistakes.

Suggest how each of the mistakes should be corrected.

The missing reagent is added and the mistakes are corrected.

Identify the liquid(s), J, K, L and M, that would react in each test.

State the expected observation for each reaction.

Liquid(s) that react in Test 1

Expected observation

Liquid(s) that react in Test 2

Expected observation

Liquid(s) that react in Test 3

Expected observation

Liquid(s) that react in Test 4

Expected observation

Figure 10 shows the apparatus that is used to separate a mixture of liquids K and M using fractional distillation.

Suggest labels that should be added to positions S, T and U in Figure 10.

Explain why fractional distillation is preferred to simple distillation to separate liquids K and M.

A gas syringe that does not have any graduations is calibrated using a known mass of propanone (boiling point = 56.2 °C).

The sealed gas syringe contains 0.146 g of propanone (M_r = 58.0) at a temperature of 95 °C and a pressure of 103 kPa

Calculate the volume, in cm³, of propanone in the gas syringe.

The gas constant, R = 8.31 J K⁻¹ mol⁻¹

The gas syringe is then cooled to 75 °C, without changing the pressure.

Calculate the decrease in volume.

(If you were unable to calculate the volume in Question 07.1, you should use the volume 89 cm³. This is not the correct answer.)

The total uncertainty in using the balance to measure the mass of propanone in Question 07.1 is ±0.001 g

Calculate the uncertainty that this causes in the volume, in cm³, of propanone calculated in Question 07.1.

(If you were unable to calculate the volume in Question 07.1, you should use the volume 89 cm³. This is not the correct answer.)

A 600 cm³ sample of propanone is mixed with 2800 cm³ of oxygen in a container at 60 °C and 100 kPa. The mixture is ignited. When the reaction is complete, the remaining mixture of gases is cooled to 60 °C at 100 kPa

Calculate the total volume of the remaining gas mixture.

This question is about biofuels.

Palmitic acid, CH₃(CH₂)₁₄COOH, can be made by hydrolysis of the triester in palm oil under acidic conditions. Palmitic acid can be used as a biofuel.

Complete the equation for the hydrolysis of the triester in palm oil under acidic conditions.

Palmitic acid burns in air.

In a calorimetry experiment, combustion of 387 mg of palmitic acid increases the temperature of 0.150 kg of water from 23.9 °C to 37.5 °C

Calculate a value, in kJ mol^–1, for the enthalpy of combustion of palmitic acid in this experiment. Give your answer to the appropriate number of significant figures.

The specific heat capacity of water is 4.18 J K^–1 g^–1

State how the value calculated in Question 08.2 is likely to differ from data book values.

Give one reason, other than heat loss, for this difference.

A sample of a different biofuel, made from sewage sludge, is found to contain 37.08% carbon, 5.15% hydrogen and 24.72% oxygen by mass. The rest of the sample is sulfur.

Calculate the empirical formula of this biofuel.

Empirical formula

Complete combustion of the biofuel made from sewage sludge produces the greenhouse gas carbon dioxide.

Suggest one other possible environmental problem with the complete combustion of this biofuel.

State the formula of the pollutant responsible for this problem.

Environmental problem

Ethanol is a biofuel that can be produced by the fermentation of glucose.

Glucose has the structural formula shown.

Table 3 shows some mean bond enthalpy values.

Use the equation and the data in Table 3 to calculate an approximate value of Δ H for the fermentation of glucose. For this calculation you should assume that all the substances are in the gaseous state.

The carbon dioxide produced from fermentation can be reacted with steam to make more ethanol.

The equation for this reaction is

Table 4 shows some standard enthalpies of formation.

Use the data in Table 4 to calculate a standard enthalpy change value for this reaction.

This question is about ethanoic anhydride.

In the gas phase, ethanoic anhydride (CH₃CO)₂O decomposes to form ethenone.

The equation is

Ethenone is the simplest member of the ketene homologous series. Ketenes all contain one C=C double bond and one C=O double bond.

Deduce the general formula for the ketene homologous series.

Figure 11 shows an incomplete suggested mechanism for the decomposition of ethanoic anhydride.

Complete the mechanism in Figure 11 by adding three curly arrows and any relevant lone pairs of electrons.

For a chemical reaction the relationship between the rate constant, k, and the temperature, T, is shown by the Arrhenius equation.

For the decomposition of gaseous ethanoic anhydride

the activation energy, E_a = 34.5 kJ mol^–1

At temperature T₁ the rate constant, k = 2.48 10⁸ s^–1

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

Sketch the Maxwell–Boltzmann distribution of molecular energies for gaseous ethanoic anhydride at temperature T₁ and at a higher temperature T₂

Include a label for each axis, and mark on the appropriate axis a typical position for the activation energy.

Explain why the rate of reaction is faster at T₂

Explanation