AQA A Level Chemistry Paper 1 November 2021 question paper 7405/1

This question is about enthalpy changes for calcium chloride and magnesium chloride.

State the meaning of the term enthalpy change.

Figure 1 shows an incomplete Born–Haber cycle for the formation of calcium chloride.

Complete Figure 1 by writing the formulas, including state symbols, of the appropriate species on each of the three blank lines.

Table 1 shows some enthalpy data.

Use Figure 1 and the data in Table 1 to calculate a value for the enthalpy of lattice dissociation of calcium chloride.

Magnesium chloride dissolves in water.

Give an equation, including state symbols, to represent the process that occurs when the enthalpy of solution of magnesium chloride is measured.

Table 2 shows some enthalpy data.

Use your answer to Question 01.4 and the data in Table 2 to calculate a value for the enthalpy of solution of magnesium chloride.

The enthalpy of hydration of Ca²⁺(g) is –1650 kJ mol^–1

Suggest why this value is less exothermic than that of Mg²⁺(g)

This question is about atomic structure.

Define the mass number of an atom.

Complete Table 3 to show the numbers of neutrons and electrons in the species

A sample of titanium contains four isotopes,⁴⁶Ti,⁴⁷Ti,⁴⁸Ti and⁴⁹Ti This sample has a relative atomic mass of 47.8 In this sample the ratio of abundance of isotopes⁴⁶Ti,⁴⁷Ti and⁴⁹Ti is 2:2:1

Calculate the percentage abundance of⁴⁶Ti in this sample.

This question is about elements in Period 3 and their compounds.

When a piece of sodium is added to 200 cm³ of water in a large beaker a vigorous reaction occurs. The temperature of the water increases by 25^oC

Give an equation, including state symbols, for the reaction of sodium with water.

Suggest why it is dangerous to react a similar piece of sodium with 10 cm³ of water in a boiling tube.

Equation

Why it is dangerous

Give an equation for the reaction of phosphorus(V) oxide with water.

Suggest a pH for the solution formed.

Equation

Explain, in terms of crystal structure and bonding, why silicon(IV) oxide has a higher melting point than phosphorus(V) oxide.

An element in Period 3 forms an oxide that is insoluble in water. This oxide reacts with sulfuric acid and with aqueous potassium hydroxide.

Give the formula for this oxide.

Give an equation for the reaction of this oxide with sulfuric acid.

Equation

Give the formula of a hydroxide of an element in Period 3 used in medicine.

Identify the element in Period 3, from sodium to chlorine, that has the largest atomic radius.

This question is about iron and its ions.

Discuss the role of iron as a heterogeneous catalyst in the Haber process.

Your answer should include:

• the meaning of the term heterogeneous catalyst

• how iron acts as a heterogeneous catalyst

• the factors that affect the efficiency and lifetime of the catalyst.

Fe²⁺ ions catalyse the reaction between peroxodisulfate(VI) ions and iodide ions in aqueous solution.

Explain why this reaction is slow before the catalyst is added. Give two equations to show how Fe²⁺ ions catalyse this reaction.

Why reaction is slow before catalyst added

Equation 1

Equation 2

Give a reason why Zn²⁺ ions do not catalyse the reaction in Question 04.2.

Iron reacts with dilute hydrochloric acid to form iron(II) chloride and hydrogen.

A 0.998 g sample of pure iron is added to 30.0 cm³ of 1.00 mol dm^–3 hydrochloric acid.

One of these reagents is in excess and the other reagent limits the amount of hydrogen produced in the reaction.

Calculate the maximum volume, in m³, of hydrogen gas produced at 30^oC and 100 kPa.

Give your answer to 3 significant figures.

In your answer you should identify the limiting reagent in the reaction.

The gas constant, R = 8.31 J K⁻¹ mol⁻¹

Figure 2 shows some reactions of iron ions in aqueous solution.

Identify A and state its colour.

Give the formula of B and state its colour.

Give an ionic equation for the reaction of [Fe(H₂O)₆]³⁺ with aqueous Na₂CO₃ to form B.

Ionic equation

Explain why an aqueous solution containing [Fe(H₂O)₆]³⁺ ions has a lower pH than an aqueous solution containing [Fe(H₂O)₆]²⁺ ions.

This question is about the equilibrium

State and explain the effect, if any, of a decrease in overall pressure on the

Calculate the partial pressure, in kPa, of SO₂ in this equilibrium mixture.

Table 4 shows the partial pressures of the gases at equilibrium.

Give an expression for the equilibrium constant (K_p) for this reaction.

Calculate the value of the equilibrium constant for this reaction and give its units.

What is the effect on the value of K_p if the pressure of this equilibrium mixture is increased at a constant temperature?

Tick (✓) one box.

This question is about pH.

Pure water dissociates slightly.

The ionic product of water, K_w = [H⁺][OH⁻]

Explain why [H₂O] is not shown in the K_w expression.

Table 5 shows how K_w varies with temperature.

Explain why the value of K_w increases as the temperature increases.

Give the expression for pH.

Calculate the pH of pure water at 50 °C Give your answer to 2 decimal places.

Explain why water is neutral at 50 °C

Calculation

A pH meter is calibrated using a calibration graph. To create the calibration, the pH meter is used to measure the pH of separate solutions, each with a known, accurate pH.

Figure 3 shows the calibration graph.

Use Figure 3 to give the true pH value when the pH meter reading is 5.6

Suggest why the pH probe is washed with distilled water between each of the calibration measurements.

The calibrated pH meter is used to monitor the pH during a titration of hydrochloric acid with sodium hydroxide.

Explain why the volume of sodium hydroxide solution added between each pH measurement is smaller as the end point of the titration is approached.

Table 6 shows data about some indicators.

The student plans to do the titration again using one of the indicators in Table 6 to determine the end point.

State why all three of the indicators in Table 6 are suitable for this titration.

36.25 cm³ of 0.200 mol dm^–3 sodium hydroxide solution are added to 25.00 cm³ of 0.150 mol dm^–3 hydrochloric acid.

Calculate the pH of the final solution at 25 ºC

This question is about thermodynamics. Consider the reaction shown.

Table 7 shows some thermodynamic data.

Explain why the standard entropy value for carbon dioxide is greater than that for carbon.

State the temperature at which the standard entropy of aluminium is 0 J K^–1 mol^–1

Use the equation and the data in Table 7 to calculate the minimum temperature, in K, at which this reaction becomes feasible.

This question is about electrode potentials and electrochemical cells.

State the meaning of the term electrochemical series.

Table 8 shows some electrode potentials.

State two conditions needed for the following half-cell to have = 0.00 V

Identify the weakest reducing agent in Table 8.

Use half-equations from Table 8 to deduce an equation for the reduction of VO₂⁺ to form VO²⁺ in aqueous solution by iron.

Use data from Table 8 to explain why [Co(H₂O)₆]³⁺(aq) will undergo a redox reaction

Give an equation for this reaction.

Equation

Suggest why the two cobalt(III) complex ions in Table 8 have different electrode potentials.

This question is about the development of lithium cells. The value of for lithium suggests that a lithium cell could have a large EMF.

Table 9 shows some electrode potential data.

Use data in Table 9 to explain why an aqueous electrolyte is not used for a lithium cell.

In the 1970s lithium-iodine cells became a common power source for

Use the data in Table 9 to calculate the cell EMF of a standard lithium-iodine cell.

An EMF value for a commercial lithium-iodine cell is 2.80 V

Suggest why this value is different from the value calculated in Question 09.2.

In some lithium cells, lithium perchlorate (LiClO₄) is used as the electrolyte.

Deduce the oxidation state of chlorine in LiClO₄

In other lithium cells, lithium cobalt oxide electrodes and lithium electrodes are used.

Give an equation for the reaction that occurs at the positive lithium cobalt oxide electrode.

Give an equation for the reaction that occurs at the negative lithium electrode.