AQA A Level Chemistry Paper 2 November 2021 question paper 7405/2

Coconut oil contains a triester with three identical R groups. This triester reacts with potassium hydroxide.

Complete the equation by drawing the structure of the other product of this reaction in the box.

Name the type of compound shown by the formula RCOOK

Give one use for this type of compound.

The triester in coconut oil has a relative molecular mass, M_r = 638.0 In the equation shown at the start of Question 01, R represents an alkyl group that

A 1.450 g sample of coconut oil is heated with 0.421 g of KOH in aqueous ethanol until all of the triester is hydrolysed. The mixture is cooled. The remaining KOH is neutralised by exactly 15.65 cm³ of 0.100 mol dm^–3 HCl

Calculate the percentage by mass of the triester (M_r= 638.0) in the coconut oil.

Suggest why aqueous ethanol is a suitable solvent when heating the coconut oil with KOH.

Give a safety precaution used when heating the mixture. Justify your choice.

Safety precaution

This question is about fuels.

The petrol fraction obtained from crude oil can be used as fuel in cars.

State the meaning of fraction, as used in the term petrol fraction.

Hexadecane (C₁₆H₃₄) can be cracked at high temperature to form petrol.

Complete the equation to show the cracking of one molecule of hexadecane to form hexane and cyclopentane only.

Give the name of a catalyst used in this cracking reaction.

Carbon dioxide is formed when petrol is burned. Carbon dioxide acts as a greenhouse gas when it absorbs infrared radiation.

Give a reason why carbon dioxide absorbs infrared radiation.

Compound Z (HOCH₂CH₂NH₂) can be used to remove carbon dioxide from the mixture of waste gases produced in some power stations.

Figure 1 shows part of a suggested mechanism for the reaction of Z with carbon dioxide.

Draw two curly arrows to complete the mechanism in Figure 1.

Name compound Z (HOCH₂CH₂NH₂)

Deduce the role of Z in step 2 of the mechanism.

HOCH₂CH₂NH₂ can be represented as XNH₂ [HOCH₂CH₂NH₃]⁺ can be represented as [XNH₃]⁺

Draw the shape of XNH₂ and of [XNH₃]⁺

State whether the H–N–H bond angle in XNH₂ is greater than, the same as, or smaller than that in [XNH₃]⁺

Explain your answer.

Shape of XNH₂ Shape of [XNH₃]⁺

Bioethanol is used as an alternative to fossil fuels.

This statement appeared on a website.

“The fact that bioethanol is a carbon-neutral fuel outweighs the environmental disadvantages of producing bioethanol.”

Evaluate this statement.

In your answer you should include:

• an outline of how bioethanol is produced

• relevant equations

• analysis of the environmental impacts.

A student does an experiment to determine a value for the enthalpy of combustion of heptane. Figure 2 shows some of the apparatus used.

Design a table to record all the readings necessary to determine an experimental value for the enthalpy of combustion for heptane in this experiment.

The student considered using a glass beaker on a tripod and gauze instead of the clamped copper calorimeter.

Suggest two disadvantages of using a glass beaker on a tripod and gauze.

Suggest two reasons why the value of enthalpy of combustion from this experiment is less exothermic than a data book value.

Suggest one addition to this apparatus that would improve the accuracy of the enthalpy value obtained.

Use Figure 3 and the data shown in Table 1 to calculate ΔH₂

A mixture of concentrated nitric acid and concentrated sulfuric acid reacts with benzene.

Figure 4 shows the incomplete mechanism for this reaction.

Name the mechanism.

Complete the mechanism in Figure 4 by adding

• any lone pairs of electrons involved in each step

• two curly arrows in step 1

• a curly arrow in step 2

• a curly arrow in step 3

• a curly arrow in step 4.

Name of mechanism

This question is about equilibrium.

1 mol of a diester with molecular formula C₇H₁₂O₄ is added to 1 mol of water in the presence of a small amount of catalyst. The mixture is left to reach equilibrium at a constant temperature.

At equilibrium, mol of ethanoic acid are present in the mixture.

Complete Table 2 by deducing the amounts, in terms of , of the diester, water and diol present in the equilibrium mixture.

Deduce the structure of the diester in Question 05.1

A new equilibrium mixture of the substances from Question 05.1 is prepared at a different temperature.

Table 3 shows the amount of each substance in this new equilibrium mixture.

The value of the equilibrium constant, K_c is 0.161 at this temperature.

Calculate the amount of water, in mol, in this new equilibrium mixture. Show your working.

This question is about isomers with the molecular formula C₅H₁₀O

Draw the skeletal formula of a branched chain aldehyde with molecular formula C₅H₁₀O that is optically active.

Describe how you distinguish between separate samples of the two enantiomers of the branched chain aldehyde C₅H₁₀O

Draw the E and Z forms of a structural isomer of C₅H₁₀O that shows both optical and geometric isomerism.

Isomer J is cyclic and has an ether functional group (C–O–C) Isomer J has only three peaks in its¹³C NMR spectrum.

Draw two other cyclic isomers of C₅H₁₀O that have an ether functional group and only three peaks in their¹³C NMR spectra.

This question is about spectroscopy.

Compound K has molecular formula C₄H₈O Figure 5 shows the infrared spectrum of K.

Which functional group does K contain?

Tick (✓) one box.

Compound L has molecular formula C₄H₇NO Figure 6 shows the infrared spectrum of L.

L reacts with H₂ in the presence of a nickel catalyst to give compound M.

Suggest three ways in which the infrared spectrum of M is different from the infrared spectrum of L.

Figure 7 shows the¹H NMR spectrum of Q, C₃H₇ClO

Table 4 shows the chemical shifts (δ values) and integration values for each peak.

Explain your answer.

This question is about making a diester from cyclohexanol.

State the type of reaction in step 1.

Give the name of the reagent needed for step 1.

State the reagents needed and give equations for step 2 and step 3.

Show the structure of Compound G in your equations.

Step 2 equation

Step 3 equation

Cyclohexane-1,2-diol reacts with ethanedioyl dichloride.

Give the name of the mechanism for this reaction.

Complete the mechanism to show the formation of one ester link in the first step of this reaction.

Mechanism

Suggest why chemists usually aim to design production methods

• with fewer steps

• with a high percentage atom economy.

High percentage atom economy

This question is about the ozone layer in the upper atmosphere.

State why the ozone layer is beneficial for living organisms.

State how chlorofluorocarbons (CFCs) form chlorine atoms in the upper atmosphere.

Give equations to show how chlorine atoms catalyse the decomposition of ozone.

Hydrochlorofluorocarbons (HCFCs) have been used in place of CFCs. In the mechanism to make an HCFC from a fluoroalkane, two incomplete steps are shown.

Complete each step in the mechanism.

Give the name of the type of step shown by both these equations.

This question is about rates of reaction. Iodine and propanone react together in an acid-catalysed reaction

A student completed a series of experiments to determine the order of reaction with respect to iodine.

Method

• Transfer 25 cm³ of 1.0 mol dm^–3 propanone solution into a conical flask.

• Add 10 cm³ of 1.0 mol dm^–3 HCl(aq)

• Add 25 cm³ of 5.0 10^–3 mol dm^–3 I₂(aq) and start a timer.

• At intervals of 1 minute, remove a 1.0 cm³ sample of the mixture and add each sample to a separate beaker containing an excess of NaHCO₃(aq)

• Titrate the contents of each beaker with a standard solution of sodium thiosulfate and record the volume of sodium thiosulfate used.

Suggest why the 1.0 cm³ portions of the reaction mixture are added to an excess of

Suggest why the order of this reaction with respect to propanone can be ignored in this experiment.

The volume of sodium thiosulfate solution used in each titration is proportional to the concentration of iodine in each beaker.

Table 5 shows the results of the experiment.

Use the results in Table 5 to draw a graph of volume of sodium thiosulfate solution against time.

Draw a line of best fit.

Explain how the graph shows that the reaction is zero-order with respect to iodine in the reaction between propanone and iodine.

The Arrhenius equation can be written as

Figure 8 shows a graph of ln k against for the reaction

Use Figure 8 to calculate a value for the activation energy (E_a), in kJ mol⁻¹, for this reaction.