AQA A Level Chemistry Paper 1 June 2024 question paper 7405/1

This question is about atomic structure.

In 1897 JJ Thomson discovered the electron. He suggested that atoms were positively charged spheres with electrons embedded within them.

Figure 1 represents an atom using Thomson’s model.

Suggest the identity of this atom.

Give two differences between the modern model of an atom and the Thomson model of an atom.

Tellurium has a relative atomic mass of 127.6 Iodine has a relative atomic mass of 126.9

Define relative atomic mass.

Suggest one property of tellurium that justifies its position before iodine in the modern Periodic Table.

A sample of tellurium is analysed in a time of flight (TOF) mass spectrometer using electron impact ionisation.

Give an equation, including state symbols, for this ionisation.

In the TOF mass spectrometer an ion of an isotope of tellurium, with mass number y, travels along a 1.25 m flight tube with a kinetic energy of 1.88 x 10^–12 J

The ion takes 3.00 x 10^–7 s to reach the detector.

KE = kinetic energy / J m = mass / kg

Calculate the mass, in g, of 1 mole of these tellurium ions.

Use your answer to suggest the mass number y of the tellurium isotope.

The Avogadro constant, L = 6.022 × 10²³ mol^–1

Tellurium has several other isotopes. Two of these isotopes are¹²⁶Te and¹²⁴Te A different sample of tellurium is analysed using a TOF mass spectrometer.

Which statement about kinetic energy (KE) is correct?

Tick (✓) one box.

This question is about an experiment to determine the solubility of strontium hydroxide in water at 20 °C

Strontium hydroxide is slightly soluble in water. Strontium hydroxide solution reacts in a similar way to calcium hydroxide solution.

• Some solid strontium hydroxide is added to approximately 1 dm³ of distilled water in a stoppered flask.

• The mixture is kept at 20 °C. Every day, the mixture is checked. If no solid is present in the flask, more solid strontium hydroxide is added.

• On the day when no more solid needs to be added, the flask is opened and the mixture is filtered into another flask and stoppered.

• A 25.0 cm³ sample of the filtrate is transferred to a conical flask with a pipette and a few drops of indicator added.

• This sample is titrated with 0.100 mol dm^–3 hydrochloric acid.

• The titration is repeated several times with further samples of the filtrate. The results are shown in Table 1 on page 8.

Suggest why the solution is kept until no more solid needs to be added.

Suggest why it is important to remove the undissolved strontium hydroxide before the titration.

After the filtration, the solution is stored in a stoppered flask.

Suggest a reason for stoppering the flask.

The diagrams in Figure 2 show the part of a pipette with the graduation line.

Which diagram identifies the pipette that is correctly filled?

Tick (✓) one box.

Figure 2

Solubility can be quoted as ‘g of solute per 100 cm³ of solution’.

Table 1 shows the results of the titrations between strontium hydroxide and hydrochloric acid. These can be used to determine the solubility of strontium hydroxide.

Give the equation for the reaction between strontium hydroxide and hydrochloric acid.

Use the results in Table 1 to calculate the mean titre.

Use the mean titre to calculate the solubility of strontium hydroxide, in g per 100 cm³ of solution, at 20 °C

Equation

This question is about aqueous ions of the metal iron.

When an aqueous [Fe(H₂O)₆]³⁺ ion reacts with ethanedioate ions, an iron(III) complex ion X is formed.

The only ligands in X are ethanedioate ions.

Draw the structure of X.

Include the charge.

The formation of X is an example of the chelate effect.

Explain the meaning of the chelate effect.

Outline how Fe²⁺ ions catalyse the reaction between S₂O₈^2– ions and I^– ions in aqueous solution.

In your answer you should include

• a sketch graph to show how the concentration of S₂O₈^2– ions changes over time

• an explanation of how Fe²⁺ ions catalyse the reaction, including equations

• an overall equation for the reaction.

A student adds dilute ammonia solution to a solution containing [Fe(H₂O)₆]²⁺ ions.

Give the formula of the precipitate that forms.

The student adds sodium carbonate solution to a solution containing

State one observation the student would make.

Give an equation for the reaction.

Equation

A solution containing [Fe(H₂O)₆]²⁺ ions changes to a yellow-brown colour after several hours in contact with air.

The student adds sodium carbonate to the yellow-brown solution.

Give an equation for the reaction with sodium carbonate.

This question is about some gas mixtures at equilibrium.

This reaction can be used to make hydrogen.

A mixture of 2.00 mol of H₂O(g) and 2.00 mol of CO(g) is allowed to reach equilibrium at a constant temperature in a 20 dm³ container. At equilibrium, there are 0.92 mol of H₂(g).

Calculate the mole fraction of H₂(g) in the equilibrium mixture.

State why the equilibrium constant (K_p) for this reaction has no units.

The temperature of the equilibrium mixture formed in Question 04.1 is increased.

How does the amount of H₂(g) change when the new position of equilibrium is reached?

Tick (✓) one box.

Ethanol can be made from ethene and steam.

Table 2 shows the mole fractions of each of the gases in an equilibrium mixture at 6000 kPa

Give an expression for K_p for this reaction.

Calculate the value of K_p at 6000 kPa

State the units.

State the effect, if any, of an increase in volume of the container on the value of K_p for this reaction at a constant temperature.

This question is about chlorine.

Give an equation to show how chlorine forms an acidic solution in water.

Give an equation for the reaction between chlorine and cold, dilute aqueous sodium hydroxide.

In acidic conditions, ClO₃^– ions oxidise Cl^– ions to form Cl₂

Deduce a half-equation for the oxidation of Cl^– to Cl₂

Deduce a half-equation for the reduction of ClO₃^– to Cl₂

Deduce the overall equation for this reaction.

Half-equation for the oxidation of Cl^– to Cl₂

Half-equation for the reduction of ClO₃^– to Cl₂

Overall equation

Give the equation for the reaction of solid sodium chloride with concentrated sulfuric acid.

State the role of the chloride ions in this reaction.

Equation

Draw the shape of the Cl₃^– ion. Include any lone pairs of electrons that influence the shape.

Chlorine forms an ion with the Group 3 element thallium (T l).

State and explain the bond angle in TlCl₂⁺

This question is about vanadium ions.

Table 3 shows some standard electrode potential values.

Use the data in Table 3 to explain why Zn reduces an aqueous solution of VO₂⁺ ions to V²⁺ ions, but does not reduce it any further.

Identify the species in Table 3 that can reduce an aqueous solution of VO₂⁺ to V

Two half-cells Fe²⁺(aq) / Fe(s) and VO²⁺(aq) / V³⁺(aq) are connected.

Calculate the EMF of this cell.

Give the conventional representation for this cell.

Give a half-equation for the reaction that occurs at the negative electrode.

Cell representation

Half-equation

0.151 g of impure NH₄VO₃ is added to dilute sulfuric acid to form a solution containing

All the VO₃^– ions are converted to VO₂⁺ ions.

These VO₂⁺ ions are reduced to aqueous V²⁺ ions by reaction with an excess of zinc.

The excess of zinc is removed by filtration and washed.

The filtrate, containing the V²⁺ ions, is titrated with a 0.0200 mol dm^–3 solution of

29.43 cm³ of KMnO₄ solution are needed to oxidise all the V²⁺ ions to VO₂⁺ ions.

The ionic equation for the reaction of MnO₄^– ions with V²⁺ ions is

Calculate the percentage purity of the NH₄VO₃ Give your answer to 3 significant figures.

Percentage purity

At 40 °C the ionic product of water, K_w = 2.92 × 10^–14 mol² dm^–6

Give the expression for K_w

Calculate the pH of pure water at 40 °C Give your answer to 2 decimal places.

35.0 cm³ of 0.150 mol dm^–3 aqueous sodium hydroxide are mixed with 20.0 cm³ of a 0.100 mol dm^–3 solution of hydrochloric acid. The temperature of the solution formed is 40 °C

Calculate the pH of the solution formed. Give your answer to 2 decimal places.

This question is about enthalpy changes.

Theoretical values for enthalpies of lattice dissociation can be calculated using a perfect ionic model.

State the meaning of the term perfect ionic model.

Enthalpies of lattice dissociation can also be obtained from Born–Haber cycles.

Figure 3 shows an incomplete Born–Haber cycle for the formation of sodium oxide.

Complete Figure 3 by writing formulas, including state symbols, of the appropriate species on each of the two blank lines.

Table 4 shows some enthalpy changes.

Use the data in Table 4 to calculate the enthalpy of lattice dissociation of sodium oxide.

Explain why the second electron affinity of oxygen has a positive value.

Explain why the enthalpy of lattice dissociation for sodium oxide is greater than the enthalpy of lattice dissociation for sodium chloride.

Sodium chloride dissolves in water.

Table 5 shows some more enthalpy changes.

Use the data in Table 5 to calculate the enthalpy of solution for sodium chloride.

Give a reason why data books do not contain a value for the enthalpy of solution of sodium oxide.

Calculate the temperature, in °C, at which this reaction becomes feasible.

This question is about metals and their compounds.

State why the atomic radius of calcium is greater than the atomic radius of magnesium.

Magnesium reacts with steam.

Give an equation, including state symbols, for this reaction.

Similar-sized pieces of barium and magnesium are added to separate 100 cm³ samples of dilute sulfuric acid. In each case the sulfuric acid is in excess.

The barium reacts quickly at first. After a few minutes the reaction stops, even though there is still some unreacted barium in the flask.

The magnesium reacts more slowly than the barium, but the reaction continues until all the magnesium has reacted.

Explain why

• the barium initially reacts more quickly than the magnesium

• the barium reaction stops before all the barium has reacted.

A metal nitrate X(NO₃)₂ completely decomposes when heated.

A 0.832 g sample of X(NO₃)₂ decomposes on heating to produce a total of

Deduce the identity of metal X.

The ideal gas constant, R = 8.31 J K^–1 mol^–1

Identity of metal X

Sodium reacts with aluminium and hydrogen to form solid NaAlH₄

Give an equation for this reaction.

Suggest why NaAlH₄ has a high melting point.

Equation

Give the equation for the reaction between H₃PO₄ and an excess of NaOH

Lithium is an important metal used in cells to power mobile phones.

In a lithium cell, a lithium cobalt oxide electrode and a lithium electrode are used.

Give the equation for the reaction that occurs at the positive electrode.

Commercial electrochemical cells can be rechargeable or non-rechargeable.

State why lithium cells can be recharged.