AQA A Level Chemistry Paper 2 November 2020 question paper 7405/2

Use the graph in Figure 1 to determine the initial rate of reaction for this experiment. State its units. Show your working on the graph.

Another student reacted different initial concentrations of phosphinate ions with an excess of hydroxide ions. The student measured the time (t) taken to collect 15 cm³ of hydrogen gas. Each experiment was carried out at the same temperature. Table 1 shows the results.

State the relationship between the initial concentration of phosphinate and time (t).

Deduce the order of the reaction with respect to phosphinate.

Complete the diagram in Figure 2 to show how the hydrogen gas could be collected and measured in the experiments in Questions 01.1 and 01.2.

Figure 2

The rate equation for a different reaction is

Deduce the overall effect on the rate of reaction when the concentrations of both L and M are halved.

Calculate the concentration of M if the rate constant is 21.3 mol^–2 dm⁶ s^–1

Define the term overall order of reaction.

Prilocaine is used as an anaesthetic in dentistry. Figure 3 shows the structure of prilocaine.

Draw a circle around any chiral centre(s) in Figure 3.

Identify the functional group(s) in the prilocaine molecule.

Tick (✓) the box(es) corresponding to the functional group(s).

Prilocaine is completely hydrolysed in the human body to give a mixture of products.

Draw the structures of the two organic products formed in the complete hydrolysis of prilocaine in acidic conditions.

Figure 4 shows optical isomers F and G.

Isomer F is the active compound in the medicine ibuprofen.

In the manufacture of ibuprofen both isomers F and G are formed. An enzyme is then used to bind to isomer G and catalyse its hydrolysis.

After the products of hydrolysis of G are removed, a pure sample of isomer F is collected.

Explain how a structural feature of this enzyme enables it to catalyse the hydrolysis of isomer G but not the hydrolysis of isomer F.

This question is about the structural isomers shown.

Identify the isomer(s) that would react when warmed with acidified potassium dichromate(VI).

State the expected observation when acidified potassium dichromate(VI) reacts.

Expected observation

State the type of structural isomerism shown by isomers P, Q, R and S.

Describe fully how infrared spectra can be used to distinguish between isomers R, S and T. Use data from Table A in the Data Booklet in your answer.

State why mass spectrometry using electrospray ionisation is not a suitable method to distinguish between the isomers.

Describe the instruction that is missing from step 4 of the method.

Justify why this step is necessary.

Suggest a suitable piece of apparatus to measure out the ethanoic anhydride in step 5.

Identify a hazard of using concentrated phosphoric acid in step 6.

Complete the equation for the reaction of salicylic acid with ethanoic anhydride to produce aspirin.

A 6.01 g sample of salicylic acid (M_r = 138.0) is reacted with

The density of ethanoic anhydride is 1.08 g cm^–3

Show by calculation which reagent is in excess.

Calculate the mass, in g, of aspirin (M_r = 180.0) produced.

Suggest two ways in which the melting point of the crude aspirin collected in step 9 would differ from the melting point of pure aspirin.

The crude aspirin can be purified by recrystallisation using hot ethanol (boiling point = 78 °C) as the solvent.

Describe two important precautions when heating the mixture of ethanol and crude aspirin.

The pure aspirin is filtered under reduced pressure. A small amount of cold ethanol is then poured through the Buchner funnel.

Explain the purpose of adding a small amount of cold ethanol.

A sample of the crude aspirin is kept to compare with the purified aspirin.

Describe one difference in appearance you would expect to see between these two solid samples.

This question is about 2-bromopropane.

Define the term electronegativity.

Explain the polarity of the C–Br bond in 2-bromopropane.

Electronegativity

Draw the skeletal formula of the main organic species formed in the reaction between a large excess of 2-bromopropane and ammonia.

Give a use for the organic product.

Skeletal formula

State the type of reaction in step 1.

Identify the reagent(s) and conditions needed for step 1.

State the name of the mechanism for the reaction in step 2.

Identify the inorganic reagent needed for step 2.

Name the organic product of step 2.

Name of mechanism

Name of organic product

The organic product of step 2 is reacted with concentrated sulfuric acid in step 3.

Outline the mechanism for step 3.

Draw the repeating unit of polystyrene.

This question is about NMR spectroscopy.

A compound is usually mixed with Si(CH₃)₄ and either CCl₄ or CDCl₃ before recording the compound’s¹H NMR spectrum.

State why Si(CH₃)₄, CCl₄ and CDCl₃ are used in¹H NMR spectroscopy.

Explain how their properties make them suitable for use in¹H NMR spectroscopy.

Deduce the splitting pattern for each of the peaks given by the H atoms labelled x, y and z in the¹H NMR spectrum of the compound shown.

Suggest why it is difficult to use Table B in the Data Booklet to predict the chemical shift ( value) for the peak given by the H atom labelled y.

Two isomers of CH₃CHClCOCH(CH₃)₂ each have two singlet peaks only in their

In both spectra the integration ratio for the two peaks is 2:9

Deduce the structures of these two isomers.

Isomer 1

Isomer 2

This question is about citric acid, a hydrated tricarboxylic acid. Its formula can be

A 1.50 g sample of H₃Y.H₂O contains 0.913 g of oxygen by mass. The sample burns completely in air to form 1.89 g of CO₂ and 0.643 g of H₂O

Show that the empirical formula of citric acid is C₃H₅O₄

A 3.00 g sample of H₃Y.H₂O (M_r = 210.0) is heated to constant mass. The anhydrous H₃Y that remains has a mass of 2.74 g

Show, using these data, that the value of = 1

Figure 5 shows the structure of H₃Y

Complete this IUPAC name for H₃Y

State the number of peaks you would expect in the¹³C NMR spectrum for H₃Y

A and B react together to form an equilibrium mixture.

An aqueous solution containing 0.25 mol of A is added to an aqueous solution containing 0.25 mol of B.

When equilibrium is reached, the mixture contains 0.015 mol of C.

Calculate the amount of A and the amount of B, in moles, in the equilibrium mixture.

At a different temperature, another equilibrium mixture contains 0.30 mol of A, 0.25 mol of B and 0.020 mol of C in 350 cm³ of solution.

Calculate the value of the equilibrium constant K_c

When an excess of water is added to chloroethanal, an equilibrium mixture is formed.

An expression for an equilibrium constant (K) for the reaction under these conditions is

Suggest why an expression for K can be written without the concentration of water.

Distilled water is added to 4.71 g of chloroethanal (M_r = 78.5) to make 50.0 cm³ of solution. The mixture is allowed to reach equilibrium.

The value of the equilibrium constant (K) is 37.0

Calculate the equilibrium concentration, in mol dm^–3, of ClCH₂CH(OH)₂

When an excess of water is added to ethanal a similar nucleophilic addition reaction occurs.

Suggest why this reaction is slower than the reaction in Question 09.5.