AQA A Level Chemistry Paper 3 June 2023 question paper 7405/3

Ethyl ethanoate can be made by reacting ethanol with ethanoic acid in the presence of concentrated sulfuric acid.

1. A mixture of ethanol, ethanoic acid, and concentrated sulfuric acid, with anti-bumping granules, is heated under reflux for 10 minutes.

2. The apparatus is rearranged for distillation.

3. The mixture is heated to collect the liquid that distils between 70 and 85 C

4. The distillate is placed in a separating funnel. Aqueous sodium carbonate is added, and a stopper is placed in the funnel. The mixture is shaken, releasing pressure as necessary.

5. The lower aqueous layer is removed and the upper organic layer is placed in a small conical flask.

6. Anhydrous calcium chloride is added to the sample in the conical flask. The flask is shaken well and left for a few minutes.

7. The liquid from the flask is redistilled and the distillate is collected between

State the role of concentrated sulfuric acid in this reaction.

The reaction mixture is flammable.

Suggest how the reaction mixture should be heated in step 1.

Figure 1 shows how a student set up the apparatus for reflux in step 1. You should assume that the apparatus is clamped correctly.

Identify two mistakes the student made in setting up the apparatus. State the problem caused by each mistake.

State why sodium carbonate is added to the distillate in step 4.

Explain why there is a build-up of pressure in the separating funnel.

Give a reason why two layers form in the separating funnel.

Suggest why ethyl ethanoate forms the upper layer.

State why anhydrous calcium chloride is added in step 6.

A student uses the method to prepare some ethyl ethanoate.

The student adds 10.0 cm³ of ethanol (M_r = 46.0) to 5.25 g of ethanoic acid (M_r = 60.0) and obtains 5.47 g of ethyl ethanoate (M_r = 88.0).

For ethanol, density = 0.790 g cm^–3

Determine the limiting reagent.

Calculate the percentage yield of ethyl ethanoate.

Suggest a reason why the percentage yield is not 100%.

This question is about isomerism and the dehydration of alcohols.

Pentan-2-ol has the molecular formula C₅H₁₂O

Draw the displayed formula of an unbranched position isomer of pentan-2-ol that can be dehydrated to form a single alkene.

Draw the skeletal formula of a chain isomer of pentan-2-ol that can be dehydrated to form a mixture of alkenes.

Draw the structure of an unbranched functional group isomer of pentan-2-ol.

Another isomer of pentan-2-ol is an alcohol that is not dehydrated when heated with concentrated sulfuric acid.

Draw the structure of this isomer.

An incomplete mechanism for the dehydration of a compound is shown.

Complete the mechanism for this reaction by drawing two curly arrows on the intermediate.

Name the mechanism for this reaction.

An isomer of the final product can also form in the reaction in Question 02.5.

Draw the structure of this isomer.

Endomorphin - 2 is a peptide with the amino acid sequence shown.

Tyr–Pro–Phe–Phe–NH₂

Each amino acid is represented by a three-letter abbreviation.

Tyr = tyrosine Pro = proline Phe = phenylalanine

Figure 2 shows part of the structure of endomorphin - 2, showing the Tyr–Pro–Phe– part of the molecule.

The –NH₂ at the end of the amino acid sequence of endomorphin-2 shows that the terminal functional group is an amide, not an acid.

Complete the structure of endomorphin-2 in Figure 2.

Use the structure in Figure 2 to draw the skeletal formula of proline, Pro.

A student hydrolyses a sample of endomorphin - 2 to break it down into its constituent amino acids.

The student analyses the resulting mixture by thin-layer chromatography, TLC.

State a reagent and the conditions needed for the hydrolysis.

Figure 3 shows the apparatus used for the TLC.

There is a piece of the apparatus missing from Figure 3. This omission will result in an inaccurate chromatogram.

Identify the missing piece of the apparatus.

State and explain why this piece of the apparatus is needed.

State why the amino acids separate on the TLC plate.

When the solvent has risen up the TLC plate, the student removes the plate from the beaker and sprays it with a developing agent.

Figure 4 shows the result.

Name a suitable developing agent.

State why the developing agent is needed.

Determine the R_f value for Tyr.

A student is given two aqueous solutions, L and M, that both contain iron salts.

The student does a series of tests on the solutions.

Table 1 shows these tests and the observations.

Identify L and M using the results in Table 1.

In your answer:

• identify all precipitates

• explain why effervescence is seen in the reaction of sodium carbonate with L but not with M

• give ionic equations for all reactions.

The molar enthalpy of vaporisation (H_vap) of a liquid is the enthalpy change when one mole of liquid is converted to vapour at the boiling point of the liquid.

A student does an experiment to determine H_vap for water.

The student:

• places a large beaker on a balance

• pours 500 cm³ of water into the beaker

• uses a 2.4 kW heater to raise the temperature of the water to 100 C

• records the mass of the beaker and hot water

• uses the 2.4 kW heater to boil the water for 100 s

• records the mass of the beaker and remaining water.

The loss in mass is 103 g

Calculate H_vap for water.

Table 2 shows some data about three compounds that all contain the same number of electrons.

All three compounds in Table 2 are polar. Ethanol is the most polar and ethylamine is the least polar.

Explain why all three molecules are polar and why ethylamine is the least polar. In your answer refer to the shapes around, and relative electronegativities of, the most electronegative atoms.

Explain the trend in the boiling points of the three compounds. Refer to the intermolecular forces in all three compounds in your answer.

Calcium hydroxide is almost insoluble in water, but it reacts with dilute hydrochloric acid.

A student adds 100 cm³ of 0.100 mol dm^–3 hydrochloric acid to 0.600 g of solid calcium hydroxide.

Show, by calculation, that the calcium hydroxide is in excess.

The final mixture contains a saturated solution of Ca(OH)₂ at 293 K

At 293 K

• the solubility of Ca(OH)₂ in this solution is 0.400 g dm^–3

• K_w = 6.80 × 10^–15 mol² dm^–6

Calculate the pH of this solution. Give your answer to two decimal places.

Section B

all questions in this section.

Which row shows the number of each fundamental particle in one²⁵Mg²⁺ ion?

What is the relative molecular mass (M_r) of benzene-1,4-dicarboxylic acid?

Which substance has significant electron delocalisation?

Which reaction has a standard enthalpy change equal to the standard enthalpy of formation for barium chloride?

This is a Maxwell–Boltzmann distribution for a gaseous reactant.

What is represented by the total area under the curve?

The rate of reaction is greater when a catalyst is used, without changing the temperature.

Which statement explains why the rate of reaction is greater with a catalyst?

When HF is added to water at 298 K, this equilibrium is established.

At equilibrium, [HF] = 7.70 × 10^–3 mol dm^–3 and [F^–] = 2.30 × 10^–3 mol dm^–3

What is the value of the equilibrium constant, in mol dm^–3, at 298 K?

In which oxide is the named element in its highest oxidation state?

What happens when water is vaporised?

Which species can behave as a Brønsted–Lowry acid in aqueous solution?

Which change causes the pH of 10 cm³ of 1.0 mol dm^–3 NaOH to be halved at 298 K?

A 0.100 mol dm^–3 solution of a weak acid has pH = 2.50

What is the value of K_a for this acid, in mol dm^–3?

Which statement is not correct about the Period 3 elements sodium to chlorine?

Equal volumes of pairs of solutions are mixed.

Which pair forms a buffer solution?

Barium metal is added to a large excess of water.

Which observation is correct and complete?

Which species is the strongest reducing agent?

Which statement about the shapes of ions is not correct?

Which compound can decolourise acidified potassium manganate(VII) solution?

Which statement about catalysts used in reactions at equilibrium, at a constant temperature, is correct?

Consider this reaction scheme.

Which step is shown with a correct reagent and a correct condition?

Which process does not involve a heterogeneous catalyst?

The equation for the complete combustion of butane is

What is the mole fraction of butane in a mixture of butane and oxygen with the minimum amount of oxygen needed for complete combustion?

Most scientists believe that the concentration of ozone in the upper atmosphere should not be allowed to decrease.

Which statement is a correct reason for this belief?

Compound X can be converted into an alcohol in a two-stage process.

What is the name of compound X ?

Which is a correct equation for the oxidation of 1-phenylethanol? [O] represents oxygen from an oxidising agent.

The skeletal formulas of two compounds are shown.

Which method would distinguish between samples of these compounds?

Which compound is the strongest base?

Which statement about enzymes is not correct?

Cisplatin has the formula [Pt(NH₃)₂Cl₂] Cisplatin is an anti-cancer drug that prevents replication of DNA.

When cisplatin bonds to DNA, which is the correct ligand replacement reaction?