AQA A Level Chemistry Paper 2 June 2024 question paper 7405/2

Propanone reacts with bromine in alkaline conditions.

The rate equation for this reaction is

Sketch a graph on the axes provided to show how, at constant temperature, the concentration of bromine changes during this reaction.

Table 1 shows the initial rate of this reaction for experiments using different mixtures containing propanone, bromine and hydroxide ions.

Complete Table 1.

Use the data from experiment 1 to calculate the rate constant k for this reaction.

Give the units for the rate constant.

Figure 1 shows an incomplete mechanism for this reaction.

Complete the mechanism in Figure 1 by adding four curly arrows and any relevant lone pair(s) of electrons.

Use evidence from the rate equation to explain why Step 1 is the rate determining step.

This question is about an equilibrium.

A 25.0 cm³ sample of a solution of P is added to a 20.0 cm³ sample of a solution of Q The mixture is allowed to reach equilibrium.

The amounts in the equilibrium mixture are

P = 0.0145 mol Q = 0.0275 mol R = 0.0115 mol S = 0.0345 mol

Calculate the amount, in moles, of P before the reaction with Q.

Use your answer to calculate the concentration, in mol dm^–3, of P in the

Give the expression for the equilibrium constant, K_c

Calculate the value of K_c and deduce its units.

Explain why the amount of S increases when water is added to the equilibrium mixture.

This question is about hydrocarbons.

Eicosane (C₂₀H₄₂) can be cracked by heating to 700 K in the presence of a catalyst.

The products are

• an aromatic hydrocarbon C₈H₁₀

• an alkane C₆H₁₄

• another alkane.

Complete the equation for this reaction.

Give a suitable catalyst for this reaction.

Figure 2 shows the¹³C NMR spectrum for the aromatic hydrocarbon C₈H₁₀

Which of these is the structure of C₈H₁₀?

Tick (✓) one box.

Cracking can also be done without a catalyst, using a temperature of 1200 K and a pressure of 7000 kPa

State the type of product that is formed in high percentage in this type of cracking.

A sample of butane has a volume of 20 cm³ at room temperature and pressure.

The sample is burned completely in 1350 cm³ of air.

The final mixture is cooled to room temperature and pressure.

Calculate the total volume of gas in the final mixture. Assume that air contains 21% by volume of oxygen.

Natural gas is used in power stations to produce electricity.

Natural gas contains sulfur impurities. Sulfur dioxide forms when these impurities are burned.

State an environmental problem caused by sulfur dioxide.

Give the formula of a compound that is used to help remove sulfur dioxide from the combustion products.

Environmental problem

Formula of compound

This question is about the preparation of an ester.

Ester F can be prepared from propan-2-ol and ethanoic acid.

Give an equation for this reaction.

Name ester F.

Equation

This method is used to prepare a sample of ester F.

Step 1 Mix 10 cm³ of propan-2-ol with 10 cm³ of ethanoic acid. Add 5 drops of concentrated sulfuric acid. Reflux this reaction mixture for 20 minutes.

Step 2 Transfer the cooled reaction mixture to a separating funnel. Add 20 cm³ of aqueous sodium carbonate and shake the mixture.

Step 3 Transfer the organic layer to a beaker and add 5 g of anhydrous magnesium sulfate. Decant off the organic liquid.

Step 4 Collect the ester using simple distillation.

Describe how Step 1 should be done.

In your description you should

• give details of suitable equipment used to add each reagent to the reflux apparatus

• draw a labelled diagram of the apparatus used for refluxing the reaction mixture

• explain any safety precautions needed other than eye protection.

In Step 2 the reaction mixture from Step 1 is shaken with aqueous sodium carbonate.

State the purpose of the sodium carbonate.

Suggest a precaution that should be taken while this mixture is shaken in the separating funnel.

Give a reason for your suggested precaution.

Purpose of sodium carbonate

Suggest how the purity of the ester can be confirmed during the distillation in Step 4.

This question is about simple test-tube reactions to identify organic liquids.

Silver nitrate solution can be used to distinguish between propanoyl chloride and 1-chloropropane.

Give the observations you would expect when a few drops of silver nitrate solution are added to separate samples of propanoyl chloride and 1-chloropropane.

Observation with propanoyl chloride

Observation with 1-chloropropane

Compounds V, W, X and Y are isomers with the molecular formula C₅H₁₀O₂

Isomers V and W are carboxylic acids with formulas that can be written as C₄H₉COOH

Give an equation for the reaction of C₄H₉COOH with sodium hydrogencarbonate.

Isomer V has an asymmetric carbon atom.

Deduce the structure of V.

Isomer W has four peaks in its¹H NMR spectrum.

Deduce the structure of W.

Deduce the integration ratio for the four peaks in the¹H NMR spectrum of W.

Integration ratio

Table 2 shows information about the peaks in the¹H NMR spectrum of isomer Y.

Draw the parts of the structure of Y that can be deduced from each of these peaks.

Deduce the structure of Y.

State how many peaks are in the¹³C NMR spectrum of Y.

Part of structure from peak at δ = 3.65 ppm

Part of structure from peak at δ = 1.19 ppm

Compound L (M_r = 88.0) contains carbon, hydrogen and oxygen only.

A 6.56 × 10^–4 mol sample of L burns completely in air to form 2.62 × 10^–3 mol of water and 2.62 × 10^–3 mol of carbon dioxide.

Deduce the formula of L. Show your working.

This question is about an organic synthesis.

Name the mechanism in Step 1.

State the reagent(s) used for Step 1.

Name of mechanism

State the reagent(s) used for Step 4.

Outline the mechanism for Step 4.

Mechanism

This question is about amines.

CH₃CHBrCH₂CH₃ reacts with NH₃

Draw the skeletal formula of the major organic product formed when

• an excess of NH₃ is used

• an excess of CH₃CHBrCH₂CH₃ is used.

Product with excess NH₃

Product with excess CH₃CHBrCH₂CH₃

Figure 3 shows a two-step synthesis to make amine G.

Complete Figure 3 by drawing the mechanism for Step 1 and the displayed formula of amine G.

Figure 4 shows two amines, P and Q.

Explain why P is a stronger base than Q.

Figure 5 shows enthalpy of hydrogenation data for cyclohexene and benzene.

It also shows predicted data for the theoretical molecule cyclohexa-1,3,5-triene.

Compare benzene and the theoretical molecule cyclohexa-1,3,5-triene in terms of:

• stability

• shape

• carbon–carbon bond lengths.

For each of these properties, suggest reasons for any differences.

Use data from Figure 5 in your answer.

Two steps in the synthesis of an aromatic amine are shown.

State the two reagents needed for Step 1.

Give an equation to show the formation of the reactive intermediate from these two reagents.

Equation

State the reagent(s) needed for Step 2.

State a possible use for the amine formed in Step 2.

This question is about enthalpy of combustion.

Limonene is found in the skin of citrus fruits.

Figure 6 shows a diagram of the apparatus used in an experiment to determine a value for the enthalpy of combustion of limonene.

When 1.31 g of limonene are burned, the temperature of the 60.0 g of water in the copper calorimeter increases by 52.1 °C

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

Calculate a value for the enthalpy of combustion, in kJ mol^–1, of limonene (C₁₀H₁₆).

Table 3 shows values, obtained by different methods, for the enthalpy of combustion of a different liquid hydrocarbon.

Suggest reasons for the differences between the values obtained by each of Methods 2 and 3, and the value obtained by Method 1 in Table 3.