OCR A Level Chemistry A Periodic table, elements and physical chemistry June 2018 question paper H432/01

A sample of boron contains the isotopes¹⁰B and¹¹B. The relative atomic mass of the boron sample is 10.8.

What is the percentage of¹¹B atoms in the sample of boron?

A 8.0%

B 20%

C 80%

D 92%

Your answer

In the compound [ICl₂]⁺ [SbCl₆]^–, the oxidation number of chlorine is –1.

What are the oxidation numbers of I and Sb in the compound?

Your answer

What is the number of hydrogen atoms in 0.125 mol of C₂H₅OH?

A 7.525 × 10²²

B 4.515 × 10²³

C 3.7625 × 10²³

D 3.612 × 10²⁴

Your answer

A student titrates a standard solution of barium hydroxide, Ba(OH)₂, with nitric acid, HNO₃.

25.00 cm³ of 0.0450 mol dm^–3 Ba(OH)₂ are needed to neutralise 23.35 cm³ of HNO₃(aq).

What is the concentration, in mol dm^–3, of the nitric acid?

A 0.0241

B 0.0482

C 0.0900

D 0.0964

Your answer

Which statement best explains why nitrogen has a larger first ionisation energy than oxygen?

A N atoms have less repulsion between p-orbital electrons than O atoms.

B N atoms have a smaller nuclear charge than O atoms.

C N atoms lose an electron from the 2s subshell, while O atoms lose an electron from the 2p subshell.

D N atoms have an odd number of electrons, while O atoms have an even number.

Your answer

In the Periodic Table, element X is in Group 2 and element Y is in Group 15 (5).

What is the likely formula of an ionic compound of X and Y ?

A X₂Y₅

B X₂Y₃

C X₃Y₂

D X₅Y₂

Your answer

Which statement about ammonium carbonate is not correct?

A It reacts with Ba(NO₃)₂(aq) to form a white precipitate.

B It effervesces with dilute nitric acid.

C It release an alkaline gas with warm NaOH(aq).

D It has the formula NH₄CO₃.

Your answer

A reaction is first order with respect to a reactant X.

Which rate–concentration graph for reactant X is the correct shape?

Your answer

The reversible reaction of sulfur dioxide and oxygen to form sulfur trioxide is shown below.

An equilibrium mixture contains 2.4 mol SO₂, 1.2 mol O₂ and 0.4 mol SO₃. The total pressure is 250 atm.

What is the partial pressure of SO₃?

A 15 atm

B 25 atm

C 100 atm

D 200 atm

Your answer

A buffer solution is prepared by mixing 200 cm³ of 2.00 mol dm^–3 propanoic acid, CH₃CH₂COOH, with 600 cm³ of 1.00 mol dm^–3 sodium propanoate, CH₃CH₂COONa.

K_a for CH₃CH₂COOH = 1.32 × 10^–5 mol dm^–3

What is the pH of the buffer solution?

A 4.58

B 4.70

C 5.06

D 5.18

Your answer

The table below shows standard entropies, S.

Substance	CO(g)	H2(g)	CH3OH(l)
S / J mol–1 K–1	197.6	130.6	239.7

What is the entropy change, S, in J mol^–1 K^–1, for the following reaction?

A –219.1

B –88.5

C +88.5

D +219.1

Your answer

The redox equilibria for a hydrogen–oxygen fuel cell in alkaline solution are shown below.

What is the equation for the overall cell reaction?

Your answer

Which enthalpy change(s) is/are endothermic?

1 The bond enthalpy of the C–H bond

2 The second electron affinity of oxygen

3 The standard enthalpy change of formation of magnesium

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

Which statement(s) explain(s) why reaction rates increase as temperature increases?

1 The activation energy is less.

2 Collisions between molecules are more frequent.

3 A greater proportion of molecules have energy greater than the activation energy.

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

Which statement(s) is/are correct for the complex Pt(NH₃)₂Cl₂?

1 One of its stereoisomers is used as an anti-cancer drug.

2 It has bond angles of 109.5°.

3 It has optical isomers.

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

This question is about enthalpy changes.

Table 16.1 shows enthalpy changes that can be used to determine the enthalpy change of hydration of fluoride ions, F –.

Explain what is meant by the term enthalpy change of hydration.

Calculate the enthalpy change of hydration of fluoride ions, F –.

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

Predict how the enthalpy changes of hydration of F – and C l – would differ.

Explain your answer.

Fluorine reacts with steam as shown in the equation below.

Average bond enthalpies are shown in the table.

Explain what is meant by the term average bond enthalpy.

Calculate the bond enthalpy of the F–F bond.

bond enthalpy =........ kJ mol^–1

* Determine the rate constant and a possible two-step mechanism for this reaction that are

consistent with these results.

A student carries out an investigation to find the activation energy, E_a, and the pre-exponential factor, A, of a reaction.

The student determines the rate constant, k, at different temperatures, T. The student then plots a graph of ln k against 1 / T as shown below.

Draw a best-fit straight line and calculate the activation energy, in J mol^–1. Give your answer to three significant figures.

Show your working.

activation energy, E_a = +........ J mol^–1

Use the graph to calculate the value of the pre-exponential factor, A.

Show your working.

Nitrogen monoxide, NO, and oxygen, O₂, react to form nitrogen dioxide, NO₂, in the reversible reaction shown in equilibrium 18.1.

Write an expression for K_c for this equilibrium and state the units.

K_c =

A chemist mixes together nitrogen and oxygen and pressurises the gases so that their total gas volume is 4.0 dm³.

• The mixture is allowed to reach equilibrium at constant temperature and volume.

• The equilibrium mixture contains 0.40 mol NO and 0.80 mol O₂.

• Under these conditions, the numerical value of K_c is 45.

Calculate the amount, in mol, of NO₂ in the equilibrium mixture.

The values of K_p for equilibrium 18.1 at 298 K and 1000 K are shown below.

Predict, with a reason, whether the forward reaction is exothermic or endothermic.

The chemist increases the pressure of the equilibrium mixture at the same temperature.

State, and explain in terms of K_p, how you would expect the equilibrium position to change.

This question is about acids and bases found in the home.

Ethanoic acid, CH₃COOH, is the acid present in vinegar.

A student carries out an experiment to determine the pK_a value of CH₃COOH.

• The concentration of CH₃COOH in the vinegar is 0.870 mol dm^–3.

• The pH of the vinegar is 2.41.

Write the expression for the acid dissociation constant, K_a, of CH₃COOH.

Calculate the pK_a value of CH₃COOH.

Give your answer to two decimal places.

Determine the percentage dissociation of ethanoic acid in the vinegar.

Give your answer to three significant figures.

Many solid drain cleaners are based on sodium hydroxide, NaOH.

• A student dissolves 1.26 g of a drain cleaner in water and makes up the solution to 100.0 cm³.

• The student measures the pH of this solution as 13.48.

Determine the percentage, by mass, of NaOH in the drain cleaner.

Give your answer to three significant figures.

Sodium carbonate, Na₂CO₃, is a base used in washing soda.

Na₂CO₃ contains the carbonate ion, CO₃^2–, shown below.

Draw the ‘ dot-and-cross ’ diagram for the carbonate ion.

Show outer electrons only and use different symbols for electrons from C and O, and any ‘extra’ electrons.

This question is about the halogen group of elements and some of their compounds.

The halogens show trends in their properties down the group.

The boiling points of three halogens are shown below.

Explain why the halogens show this trend in boiling points.

Hydrogen iodide, H I, is decomposed by heat into its elements:

The decomposition is much faster in the presence of a platinum catalyst.

Complete the enthalpy profile diagram for this reaction using formulae for the reactants and products.

• Use E_a to label the activation energy without a catalyst.

• Use E_c to label the activation energy with a catalyst.

• Use H to label the enthalpy change of reaction.

Compound A is an oxide of chlorine that is a liquid at room temperature and pressure and has a boiling point of 83 °C.

When 0.4485 g of A is heated to 100 °C at 1.00 × 10⁵ Pa, 76.0 cm³ of gas is produced.

Determine the molecular formula of compound A.

Show all your working.

Complete Table 20.1 and calculate the mean titre that the student should use for analysing the results.

The uncertainty in each burette reading is ±0.05 cm³.

Calculate the percentage uncertainty in the titre obtained from titration 1.

Give your answer to two decimal places.

Describe and explain how the student should determine the end point of this titration accurately.

Determine the relative formula mass and formula of the Group 1 iodate(V), B.

Show your working.

This question is about some reactions of d block elements and their ions.

Table 21.1 shows standard electrode potentials which will be needed within this question.

Complete the electron configuration of

a Ni atom: 1s²........

a Ni²⁺ ion: 1s²........

A standard cell is set up in the laboratory with the cell reaction shown below.

Draw a labelled diagram to show how this cell could be set up to measure its standard cell potential.

Include details of apparatus, solutions and the standard conditions required.

Standard conditions........

Predict the standard cell potential of this cell.

Use the information in Table 21.1 to help you answer both parts of this question.

Write the overall equation for the oxidation of Fe²⁺ by acidified H₂O₂.

Zinc reacts with acidified Cr₂O₇^2– ions to form Cr²⁺ ions in two stages.

Explain why this happens in terms of electrode potentials and equilibria.

Include overall equations for the reactions which occur.

* Three different reactions of copper compounds are described below.

Reaction 1: Aqueous copper(II) sulfate reacts with excess aqueous ammonia in a ligand substitution reaction. A deep-blue solution is formed, containing an octahedral complex ion, C, which is a trans isomer.

Reaction 2: Copper(I) oxide reacts with hot dilute sulfuric acid in a disproportionation reaction. A blue solution, D, and a brown solid, E are formed.

Reaction 3: Copper(II) oxide reacts with warm dilute nitric acid in a neutralisation reaction, to form a blue solution. Unreacted copper(II) oxide is filtered off, and the solution is left overnight in an evaporating basin. A hydrated salt, F, crystallises, with the percentage composition by mass: Cu, 26.29%; H, 2.48%; N, 11.59%; O, 59.63%.

Identify C – F by formulae or structures, as appropriate.

Include equations, any changes in oxidation number, and working.