OCR A Level Chemistry A Periodic table, elements and physical chemistry November 2021 question paper H432/01

Which statement describes electronegativity?

A A measure of the reactivity of an element.

B The ability of an atom to attract an electron to become a 1– ion.

C The attraction of a bonded atom for the electrons in a covalent bond.

D The attraction of an atom for a lone pair of electrons.

Your answer

A chlorate(VII) ion has a 1– charge.

What is the formula for sodium chlorate(VII)?

A NaCl O₃

B NaCl O₄

C NaCl O₇

D NaCl O₈

Your answer

The unbalanced equation for the reaction of silver with concentrated nitric acid is shown below. ….. Ag(s) + ….. NO₃^–(aq) + ….. H⁺(aq) → ….. Ag⁺(aq) +.…. NO(g) +..… H₂O(l) Which numbers for Ag and H₂O will balance the equation?

Your answer

Which sample contains the greatest number of molecules?

A 140.0 g C₂H₂

B 180.0 g C₂H₆

C 240.0 g C₄H₁₀

D 400.0 g C₆H₆

Your answer

Chromium(III) oxide, Cr₂O₃, is reduced to chromium by heating with magnesium.

What is the minimum mass of Mg required to reduce 11.4 g of chromium(III) oxide?

A 0.61 g

B 0.91 g

C 3.65 g

D 5.47 g

Your answer

A student is supplied with 100.0 cm³ of a solution of 0.400 mol dm^–3 magnesium iodide, MgI₂.

A student plans to dilute this solution so that the iodide concentration is 0.250 mol dm^–3.

What volume of water, in cm³, does the student need to add?

A 60.0

B 160.0

C 220.0

D 320.0

Your answer

Which row shows elements in order of increasing first ionisation energy?

A Ca < Si < P < N

B N < P < Si < Ca

C Ca < N < P <Si

D C < Si < P < Ca

Your answer

An equilibrium system is shown below.

Different amounts of CO, NO₂, CO₂ and NO are added to four containers, as shown below.

Which container would have the largest concentration of CO(g) at equilibrium?

Your answer

An aqueous solution of ethanoic acid, CH₃COOH, has a concentration of 0.50 mol dm^–3. pK_a for CH₃COOH = 4.76 at 25 °C.

What is the pH of the ethanoic acid solution at 25 °C?

A 2.53

B 2.68

C 4.91

D 5.06

Your answer

Two redox systems are shown below.

Which species in the two redox systems is the strongest oxidising agent?

A Fe²⁺(aq)

B Fe(s)

C Cu²⁺(aq)

D Cu(s)

Your answer

Which statement(s) explain(s) the trend in boiling points down the halogens group?

1: The induced dipole–dipole interactions (London forces) become stronger.

2: The covalent bonds become stronger.

3: The permanent dipole–dipole interactions become stronger.

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

Which statement(s) about a molecule of C l –N=O is/are correct?

1: It is a polar molecule.

2: It contains 6 lone pairs of electrons.

3: It has a bond angle of 180°.

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

NH₄Fe(SO₄)₂•12H₂O is a hydrated ‘double salt’.

A student analyses this double salt using test tube tests.

Which row(s) gives/give correct result(s) for the stated test?

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

This question is about magnesium and magnesium halides.

Magnesium has metallic bonding and is a good conductor of electricity.

Describe, with the aid of a labelled diagram, the metallic bonding in magnesium and explain why magnesium conducts electricity.

Include the correct charges on the particles in your diagram.

The 12 successive ionisation energies of magnesium are shown in Table 16.1.

Write an equation to represent the fourth ionisation energy of magnesium.

Include state symbols.

Explain how the successive ionisation energies provide evidence that magnesium is in Group 2 of the periodic table.

Electrons occupy orbitals.

In Table 16.2 below, add a tick (✓) below the ionisation numbers that are responsible for removing an electron from a full orbital in a magnesium atom.

The enthalpy change of solution for magnesium fluoride, MgF₂, can be determined indirectly using an energy cycle based on the enthalpy changes below.

Explain what is meant by enthalpy change of solution.

Calculate the enthalpy change of solution of MgF₂.

enthalpy change of solution =........ kJ mol^–1

This question is about d-block elements.

Most d-block elements are also classified as transition elements.

Explain why scandium and zinc are classified as d-block elements but are not also transition elements.

Your explanations should include full electron configurations.

What is meant by a bidentate ligand ?

* Determine the formulae of A and B. Write the ionic equation for the ligand substitution and show 3D structures for the three stereoisomers of B.

In Step 1, the student observed that bubbles of gas were produced.

Suggest the formula of the copper(II) compound which reacted with HNO₃ to form the gas, and write a full equation for the reaction.

Formula:........

Equation:........

Write an ionic equation, including state symbols, for the reaction in Step 3.

Suggest a suitable indicator for this titration and state the colour change at the end point in Step 4.

Indicator:........

Colour from........ to........

Determine the percentage, by mass, of copper in the copper ore. Give your answer to an appropriate number of significant figures.

Explain whether the calculated percentage by mass of copper would be higher, lower or the same if the following changes were made to the method.

The potassium iodide was not in excess, in Step 3.

The burette readings were read from the top of the meniscus, in Step 4.

The student then modifies the method in order to obtain a more accurate value for the percentage by mass of copper in the ore. The student decides to use 25.00 g of the copper ore in Step 1.

What further modifications should the student make to produce a more accurate value for the percentage by mass of copper in the ore?

Storage cells and fuels cells are types of electrochemical cell.

The electrode potentials for five redox systems are shown in Table 19.1.

A student sets up an electrochemical cell based on redox systems 1 and 4 in Table 19.1.

Draw a labelled diagram to show how this cell could be set up in the laboratory.

Construct the equation for the overall cell reaction.

In acid conditions, MnO₄^2–(aq) disproportionates to form MnO₂(s) and MnO₄^–(aq).

Explain, in terms of oxidation numbers, why disproportionation has taken place.

Explain, in terms of electrode potentials and equilibrium shifts why MnO₄^2– disproportionates in acid conditions. Use the information in Table 19.1.

An alkaline hydrogen-oxygen fuel cell is set up.

The overall equation for the cell reaction is shown below. 2H₂(g) + O₂(g) → 2H₂O(l) Redox system 2 in Table 19.1 is the positive electrode of this cell.

Write the half-equation at the negative electrode.

The cell potential is 1.23 V.

Calculate the electrode potential of the negative electrode.

State one important feature of a fuel cell that is different from a conventional storage cell.

This question is about chemical equilibrium.

Nitrogen monoxide, NO, and oxygen, O₂, react to form nitrogen dioxide, NO₂, in the reversible reaction shown in Equilibrium 20.1.

A dynamic equilibrium exists in a closed system.

State one other feature of a dynamic equilibrium.

Show that the formation of NO₂ in Equilibrium 20.1 is feasible at 25 °C.

Determine the maximum temperature, in K, for feasibility.

Give your answer to an appropriate number of significant figures.

A chemist investigates the equilibrium shown in Equilibrium 20.1.

The chemist mixes together 1.60 mol of NO(g) and 1.50 mol of O₂(g) in a container and the mixture is allowed to reach equilibrium.

At equilibrium:

• 75% of the NO(g) has been converted to NO₂(g)

• the total pressure is 1.21 MPa.

Calculate K_p, in MPa^–1, for Equilibrium 20.1.

Give your answer to 3 significant figures.

The chemist then repeats the experiment three times. In each experiment, the chemist makes one change but uses the same initial amounts of NO and O₂.

Complete the table to show the predicted effect of each change compared with the original experiment.

Only use the words greater, smaller or same.

This question is about how the rate of reaction is affected by changes in conditions.

A student carries out two investigations using the reaction between aqueous thiosulfate ions, S₂O₃^2–(aq), and aqueous hydrogen ions, H⁺(aq). Reaction 21.1 S₂O₃^2–(aq) + 2H⁺(aq) → S(s) + SO₂(g) + H₂O(l)

Explain how the student’s results support this rate equation.

Predict a possible two-step mechanism for Reaction 21.1. The first step is the rate-determining step.

Step 1........

Step 2........

Calculate the activation energy, E_a, for Reaction 21.1, in kJ mol^–1.

Give your answer to 3 significant figures.

E_a =........ kJ mol^–1

From the graph the student estimates the value of ln A as –2.00. (A is the pre-exponential factor.)

Explain what mistake the student has made.

This question is about acids, bases and buffers.

Sodium hydroxide, NaOH, is a strong base.

Calculate the pH of 0.140 mol dm^–3 NaOH(aq) at 298 K.

Give your answer to 2 decimal places.

Sulfuric acid reacts with sodium hydroxide as shown in Equation 22.1. Equation 22.1 H₂SO₄(aq) + 2NaOH(aq) → Na₂SO₄(aq) + 2H₂O(l) H₁ This is a neutralisation reaction.

A student carries out an experiment to determine the enthalpy change H₁ and uses this value to deduce the enthalpy change of neutralisation, _neutH.

The student measures out two solutions:

• 25.0 cm³ of 1.60 mol dm^–3 H₂SO₄(aq)

• 55.0 cm³ of 1.50 mol dm^–3 NaOH(aq) (an excess).

The temperature of each solution is the same.

The student mixes the two solutions. The temperature increases by 13.0 °C.

Show that NaOH is in excess.

Calculate the enthalpy change, H₁, for Equation 22.1, and deduce the value for the enthalpy change of neutralisation, ∆_neutH, in kJ mol^–1.

Assume that the densities of all solutions and the specific heat capacity, c, of the reaction mixture are the same as for water.

enthalpy change, H₁ =........ kJ mol^–1

enthalpy change of neutralisation, _neutH =........ kJ mol^–1

The student repeats the experiment using 50.0 cm³ of 1.60 mol dm^–3 H₂SO₄ and 110.0 cm³ of 1.50 mol dm^–3 NaOH.

Predict the increase in temperature.

Explain your reasoning.

* Nitrous acid, HNO₂, is a weak Brønsted–Lowry acid with a pK_a value of 3.34 at room temperature.

HNO₂ can be prepared by reacting N₂O₃ with water. HNO₂ is the only product.

A chemist makes up a buffer solution by the following method.

Step 1 The chemist weighs a sample of N₂O₃. Water is then added to form 100 cm³ of 0.500 mol dm^–3 HNO₂(aq).

Step 2 The chemist adds 100 cm³ of 0.150 mol dm^–3 NaOH(aq) to the 100 cm³ solution of 0.500 mol dm^–3 solution of HNO₂(aq). The resulting solution is made up to 1.00 dm³.

Explain why a buffer solution forms in Step 2. Determine the pH of this buffer solution and the mass of N₂O₃ that was used in Step 1.