AQA A Level Chemistry Paper 1 June 2022 question paper 7405/1

This question is about equilibria.

Give two features of a reaction in dynamic equilibrium.

A gas-phase reaction is at equilibrium. When the pressure is increased the yield of product decreases.

State what can be deduced about the chemical equation for this equilibrium.

Carbon monoxide and hydrogen react to form methanol.

0.430 mol of carbon monoxide is mixed with 0.860 mol of hydrogen. At equilibrium, the total pressure in the flask is 250 kPa and the mixture contains 0.110 mol of methanol.

Calculate the amount, in moles, of carbon monoxide present at equilibrium.

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

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

A different mixture of carbon monoxide and hydrogen is left to reach equilibrium at a temperature T.

Some data for this equilibrium are shown in Table 1.

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

Use the K_p value from Table 1 to calculate a value for K_p for the following reaction at temperature T.

Give the units for K_p

Rhenium has an atomic number of 75

Define the term relative atomic mass.

The relative atomic mass of a sample of rhenium is 186.3

Table 2 shows information about the two isotopes of rhenium in this sample.

Calculate the relative isotopic mass of the other rhenium isotope. Show your working.

State why the isotopes of rhenium have the same chemical properties.

A sample of rhenium is ionised by electron impact in a time of flight (TOF) mass spectrometer.

A¹⁸⁵Re⁺ ion with a kinetic energy of 1.153 × 10⁻¹³ J travels through a 1.450 m flight tube.

The kinetic energy of the ion is given by the equation KE = mv²

where m = mass / kg

KE = kinetic energy / J

Calculate the time, in seconds, for the ion to reach the detector.

The Avogadro constant, L = 6.022 × 10²³mol⁻¹

State how the relative abundance of¹⁸⁵Re⁺ is determined in a TOF mass spectrometer.

This question is about hydrogen peroxide, H₂O₂

The half-equation for the oxidation of hydrogen peroxide is

Hair bleach solution contains hydrogen peroxide.

A sample of hair bleach solution is diluted with water. The concentration of hydrogen peroxide in the diluted solution is 5.00% of that in the original solution. A 25.0 cm³ sample of the diluted hair bleach solution is acidified with dilute sulfuric acid. This acidified sample is titrated with 0.0200 mol dm⁻³ potassium manganate(VII) solution. The reaction is complete when 35.85 cm³ of the potassium manganate(VII) solution are added.

Give an ionic equation for the reaction between potassium manganate(VII) and acidified hydrogen peroxide.

Calculate the concentration, in mol dm^–3, of hydrogen peroxide in the original hair bleach solution.

(If you were unable to write an equation for the reaction you may assume that the mole ratio of potassium manganate(VII) to hydrogen peroxide is 3:4 This is not the correct mole ratio.)

State why an indicator is not added in this titration.

Give the oxidation state of oxygen in hydrogen peroxide.

Hydrogen peroxide decomposes to form water and oxygen.

Give an equation for this reaction.

Calculate the amount, in moles, of hydrogen peroxide that would be needed to produce 185 cm³ of oxygen gas at 100 kPa and 298 K

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

Equation

Hydrazine (N₂H₄) is used as a rocket fuel that is oxidised by hydrogen peroxide. The equation for this reaction in the gas phase is

The enthalpy change for this reaction, ∆ H = – 789 kJ mol

Table 3 shows some mean bond enthalpy values.

Define the term mean bond enthalpy.

Use the equation and the data in Table 3 to calculate a value for the O–O bond enthalpy in hydrogen peroxide.

This question is about acids and bases.

Calculate the pH of a 0.150 mol dm^–3 solution of ethanoic acid at 25^oC Give your answer to 2 decimal places.

For ethanoic acid, K_a = 1.74 x 10^–5 mol dm^–3 at 25^oC

Strontium is an element in Group 2.

Calculate the pH of a 0.0100 mol dm^–3 solution of strontium hydroxide at 10^oC You may assume that strontium hydroxide is completely dissociated in this solution.

At 10^oC the ionic product of water, K_w = 2.93 x 10^–15 mol² dm^–6

The pH of a barium hydroxide solution is lower at 50 °C than at 10 °C

At 50 °C a 25 cm³ sample of this barium hydroxide solution was neutralised by 22.45 cm³ of hydrochloric acid added from a burette.

Deduce the volume of this hydrochloric acid that should be added from a burette to neutralise another 25 cm³ sample of this barium hydroxide solution at 10 °C

Explain your answer

State how a buffer solution can be made from solutions of potassium hydroxide and ethanoic acid.

Give an equation for the reaction between potassium hydroxide and ethanoic acid.

State how this buffer solution resists changes in pH when a small amount of acid is added.

How buffer solution is made

Equation

How buffer solution resists pH change

A buffer solution is made by adding 2.00 g of sodium hydroxide to 500 cm³ of 1.00 mol dm^–3 ethanoic acid solution.

Calculate the pH of this buffer solution at 25 °C

Give your answer to 2 decimal places.

For ethanoic acid, K_a = 1.74 x 10^–5 mol dm^–3 at 25 °C

This question is about Period 3 elements and their compounds.

Which is not a correct statement about magnesium hydroxide?

Tick (✓) one box.

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

Identify a reagent or test that could be used to distinguish between aqueous solutions of sulfur dioxide and sulfur trioxide with the same concentrations.

State the observation in each case.

Observation with sulfur dioxide solution

Observation with sulfur trioxide solution

The mass spectrum of the element phosphorus has a peak at = 124

Give the formula of the species responsible for this peak.

Give an equation for the reaction of phosphorus(V) oxide with sodium hydroxide solution.

Draw the displayed formula of the molecule formed when phosphorus(V) oxide reacts with water.

Table 4 shows the melting points of three substances.

Explain why the melting points of these substances are different.

You should refer to the structure of and bonding in each substance.

This question is about some elements in Group 7 and their compounds.

Chlorine is added to some drinking water supplies to decrease the risk of people suffering from diseases such as cholera.

State why the amount of chlorine added must be controlled.

Give an equation for the reaction of chlorine with water to form a solution containing two acids.

Explain, with reference to electrons, why this is a redox reaction.

Equation

A student bubbles chlorine gas through a solution of sodium iodide.

State the observation the student would make.

Give an ionic equation for the reaction.

Ionic equation

The student adds a few drops of concentrated sulfuric acid to a small amount of solid sodium iodide.

Two gaseous sulfur-containing products are formed.

Give an equation for the formation of each of these sulfur-containing products.

State the role of sulfuric acid in the formation of these products.

Equation 1

Equation 2

The student adds a few drops of acidified silver nitrate solution to a solution of an unknown impure sodium halide. The student observes bubbles of gas and a colourless solution. The student bubbles the gas through calcium hydroxide solution and a white precipitate forms.

Deduce the identity of the sodium halide.

Suggest the identity of the gas.

Give an ionic equation for the formation of this gas from the impurity.

Identity of sodium halide

Ionic equation

The ClF₂⁺ ion contains two different Group 7 elements.

Use your understanding of the electron pair repulsion theory to draw the shape of this ion.

Include any lone pairs of electrons that influence the shape.

Explain why the ion has the shape you have drawn.

Suggest a value for the bond angle in the ion.

Shape

Magnesium is used in the extraction of titanium from titanium(IV) chloride.

Give an equation for this reaction.

Copper(II) complexes are coloured. The colour is caused by the d electrons of copper moving from their ground state to an excited state.

Explain why aqueous solutions containing [CuCl₄]^2– ions are yellow.

When a d electron moves from the ground state to the excited state in a copper complex, the energy change is 3.98 x 10^–19 J

Calculate the frequency, in s^–1, of the light absorbed.

State three ways in which a transition metal complex can be changed to alter its colour.

Consider the following reaction scheme in which P, Q and R are different complex ions of copper.

Name the shape of the [CuCl₄]^2– ion.

Give an ionic equation for the conversion of [CuCl₄]^2– to complex ion P.

State the colour of the solution containing the complex ion Q.

Give an ionic equation for the conversion of [CuCl₄]^2– to Q.

Equation

Identify complex ion R.

This question is about cells.

The half-equations for two electrodes that combine to make a non-rechargeable cell are

Identify the oxidising agent in this cell.

Figure 1 shows a cross-section through a rechargeable silver–zinc cell.

Suggest the function of the porous separator in Figure 1.

The standard electrode potentials for two half-equations for the silver–zinc cell are

Give an equation for the overall reaction that occurs when the cell is recharging.

The EMF of an alkaline hydrogen–oxygen fuel cell is +1.23 V The standard electrode potential for one of the electrodes in the alkaline hydrogen–oxygen fuel cell is

Give the half-equation for the other electrode and calculate its standard electrode potential.

Equation

Suggest why the EMF values of the acidic and alkaline hydrogen–oxygen fuel cells are the same.