AQA A Level Chemistry Paper 3 June 2025 question paper 7405/3

A value for enthalpy of solution can be determined from the results of a calorimetry experiment or by the application of Hess’s law.

Give the equation, including state symbols, for the process that occurs when the enthalpy of solution of potassium hydroxide is determined.

A student does an experiment to determine a value for the enthalpy of solution of potassium hydroxide.

The student uses this method.

• Add some distilled water to a measuring cylinder and record the volume.

• Pour the water into a polystyrene cup.

• Record the temperature of the water in the cup.

• Add 3.00 g of solid KOH to the water in the cup.

• Stir the solution and record the maximum temperature reached.

Table 1 shows the student’s results.

The student calculated the enthalpy of solution of potassium hydroxide

The specific heat capacity of the solution, c = 4.18 J K^–1 g^–1

Assume the density of the solution = 1.00 g cm^–3

Calculate the volume of water that the student added to the cup.

Table 2 shows some enthalpy change data.

Use the data in Table 2 to calculate the enthalpy of solution for potassium hydroxide.

Suggest why the value calculated in Question 01.3 is different from the experimental value given in Question 01.2.

The effect of reactant concentrations on the rate of a reaction is investigated.

The equation for the reaction is shown.

The experiment is done five times in the presence of thiosulfate ions and starch. The reactant concentrations are varied by changing the volume of each reactant in the mixture. The thiosulfate ions react with the iodine as it is produced, until all the thiosulfate has reacted.

After all the thiosulfate has reacted, the iodine produced in the mixture then reacts with the starch and the solution turns blue-black. The time taken for the solution to turn blue-black is recorded. If the amount of thiosulfate is the same in each experiment, the time recorded represents the time to produce the same amount of iodine in each experiment.

Table 3 shows the results of the investigation.

The amount of thiosulfate is the same in each experiment. To allow the order of reaction with respect to each reactant to be calculated, several other variables need to be controlled.

Identify three other control variables.

Control variable 1

Control variable 2

Control variable 3

The total uncertainty in the times recorded for each experiment is ±0.5 s but the stopwatch used has a measurement uncertainty of ±0.01 s

Suggest why, in each experiment, the uncertainty in the times recorded is greater than the measurement uncertainty of the stopwatch.

Calculate the percentage uncertainty in the time recorded in experiment 3.

The five experiments are repeated with the same stopwatch and the same

Suggest and explain how the method can be changed to decrease the percentage uncertainty in the times recorded.

A student does an experiment to measure the standard electrode potential of an

Figure 1 shows the apparatus the student uses.

Figure 1 shows three mistakes made by the student.

Identify each mistake and the change needed to correct it.

What feature of the voltmeter ensures that the voltmeter measures the cell EMF?

Tick (✓) one box.

The Fe³⁺/Fe²⁺ electrode is the positive electrode when the cell is set up correctly at 298 K

Give the redox equation for the overall reaction that occurs in the cell when the voltmeter is replaced with a lamp.

Table 4 shows some standard electrode potentials.

Finely powdered iron filings are added to a solution of copper(II) sulfate and the mixture is stirred.

The solution gradually changes from blue to pale green and a brown solid forms.

Use the data in Table 4 to explain these observations.

Give an ionic equation for the reaction that occurs.

Give the conventional representation of the cell that has the same overall reaction as in your equation.

Calculate the EMF, in volts, of this cell.

Equation

Conventional representation

50.0 cm³ of 0.015 mol dm^–3 Fe₂(SO₄)₃(aq) are mixed with 50.0 cm³ of

The mixture is left for several hours until equilibrium is reached.

A sample of the equilibrium mixture is titrated to determine the amount of I^–(aq) in the equilibrium mixture.

Give the expression for the equilibrium constant, K_c, for the equilibrium.

Before the titration, the sample is ‘quenched’ by adding 50 cm³ of ice-cold water.

Suggest why the sample is ‘quenched’ in this way before the titration. Explain your answer.

The amount of I^–(aq) in the equilibrium mixture is found to be 3.00 × 10^–4 mol

Calculate the value of K_c at 40 °C for the equilibrium.

Assume that the total volume of the mixture remains constant at 100 cm³

This question is about oxidation.

A student has separate unlabelled samples of propan-1-ol and propan-2-ol but does not know which sample is which alcohol.

The student plans a series of steps to identify the alcohols.

Step 1 Oxidise each sample, distilling off the organic product as it is formed. Step 2 Identify the organic products using a simple chemical test. Step 3 Confirm the identities using the infrared spectrum of each original sample.

Give further details of each step in the plan. In your answer include

• an appropriate oxidising agent used in Step 1

• equations, using [O] to represent the oxidising agent, for each reaction in Step 1

• a suitable test and expected observations in Step 2

• how the infrared spectra can be used to confirm the identities.

A primary alcohol can be oxidised to form a carboxylic acid using an excess of the oxidising agent in Question 05.1.

Give the condition needed for this reaction.

Complete the diagram, adding labels, to show how the apparatus would be set up.

During oxidation reactions, anti-bumping granules are often added to the pear-shaped flask containing the reactants.

State why anti-bumping granules are used.

This question is about rapeseed oil.

Figure 2 shows the structure of compound Q found in rapeseed oil. Each branch in the molecule is formed from a different long-chain carboxylic acid.

State the type of stereoisomerism shown in Branch A.

Q can be reacted with methanol to form three different esters.

State the number used to identify the position of the C=C bond in the name of the ester formed from Branch A.

State the number of different stereoisomers of the ester formed from Branch B.

Give a use for these esters.

Number used in the name of the ester

Number of stereoisomers

Q also reacts with NaOH

State the formula of the product, formed by Branch B in Figure 2, in this reaction.

State a use for this product.

The reaction between methylamine (CH₃NH₂) and excess bromoethane (C₂H₅Br) produces a quaternary ammonium salt.

What is the formula for the cation in this salt?

Each of the conversions shown uses KOH as a reactant.

In which conversion does KOH not act as a base?

Which statement about the use of a catalyst in a reaction is correct?

Which diagram shows a correct step in the mechanism for an elimination reaction of bromoethane?

A sample of UF₆ consists of molecules containing¹⁹F and either²³⁵U or²³⁸U atoms.

The relative molecular mass of the sample is 351.43

What is the percentage abundance of²³⁵UF₆ in the sample?

Compound X reacts with concentrated sulfuric acid to produce compound Y.

Compound Y reacts with an excess of water to produce an alcohol.

Which compound could be X ?

A piece of strontium is added to an excess of water.

Which observation is correct and complete?

Which statement about trends from left to right across Period 3 is correct?

Which statement about ionisation energies in Period 3 is not correct?

Which type(s) of stereoisomerism is/are shown by the complex ion

What is the correct structural formula for 4-chloro-2-methylpent-2-enoic acid?

0.100 mol of each of the oxides listed is added to separate 1.00 dm³ samples of water.

Which oxide produces the solution with the lowest pH?

Which property of the Group 2 elements increases with increasing atomic number?

Which electron configuration represents an element that can have a maximum oxidation state of +5 in its compounds?

Which statement is correct?

Which reaction produces an octahedral complex ion ?

Ethanol biofuel can be produced by fermentation.

Which statement about this process is correct?

Which element is in the p block in the Periodic Table?

Which statement is correct?

Which species has a tetrahedral shape?

Alkanes are obtained from crude oil by fractional distillation.

Which statement is correct?

What is the structure of a dipeptide formed from the two amino acids shown?

Equal amounts of three Period 3 elements are added to separate 100 cm³ samples of water.

Which list is correct when the solutions formed from these elements are arranged in order of decreasing pH?

The oxides P₄O₁₀ and SO₂ both react with water to form acid molecules.

Which row gives the correct shape around the central atom for each acid molecule

Which structure is correct for transplatin?

The diagram shows part of the tertiary structure for a protein. Some of the amino acids in this structure are shown using the first three letters of their names.

The general formula of an amino acid is RCH(NH₂)COOH

Interactions between amino acid R groups are shown at positions T, U, V and W.

Which two R group interactions are a type of intermolecular force and a covalent bond?

Use the Data Booklet to help you answer this question.

Which statement about enzymes is correct?

Which compound can be used as a cationic surfactant?

The hydration of 1-methylcyclopent-1-ene uses a catalyst of sulfuric acid and produces a mixture of products.

Which ion is formed during the mechanism for this reaction to give the major product?