OCR A Level Chemistry A Unified chemistry June 2023 question paper H432/03

The three elements that, when in a molecule, can form hydrogen bonds with other suitable molecules.

An element that is a solid at RTP with a simple molecular lattice structure.

The two elements with atoms containing five unpaired electrons.

The element in Period 3 that exists in the solid state as a network of atoms bonded by strong covalent bonds.

The p-block element in Period 3 that forms a compound with fluorine with octahedral molecules.

The element that forms 1– ions most readily.

The element with an average atomic mass of 1.244 10^–22 g.

These questions are from different areas of chemistry.

This question is about two salts of rubidium (atomic number 37): RbClO₃ and RbClO₄.

The oxidation number of chlorine is different in the two rubidium salts, RbClO₃ and RbClO₄.

What is the name of RbClO₄?

A student carries out an experiment to determine the enthalpy change of solution of RbClO₃ using the method below.

• A 2.00 g sample of solid RbClO₃ is added to water in a well-insulated container. The initial temperature is 23.0 °C.

• The mixture is stirred until all the RbClO₃ has dissolved. The final temperature is 21.5 °C. The final solution has a mass of 102 g.

Determine the enthalpy change of solution, _solH, of RbClO₃ in kJ mol^–1.

Assume that the specific heat capacity of the solution is the same as that of pure water.

_solH (RbClO₃) =........ kJ mol^–1

A student investigates the rate of a reaction that is 1st order with respect to hydrochloric acid, HC l (aq).

• The student carries out a reaction using 0.680 mol dm^–3 HCl(aq). The initial rate is

• The student dilutes a different sample of 0.680 mol dm^–3 HCl(aq) with water. The pH of this diluted acid is 1.50.

• The student repeats the reaction using the same volume of this diluted acid.

Determine the initial rate using this diluted acid.

initial rate =........ mol dm^–3 s^–1

Tutton’s salts are ‘double salts’ with the formula X₂Y(ZO₄)₂ • 6H₂O.

A Tutton’s salt contains two cations: X⁺ and Y²⁺.

• X + can be an ion of the Group 1 elements K, Rb, Cs or Fr, or an ammonium ion.

• Y²⁺ can be a 2+ ion of magnesium or an ion of most of the transition elements in Period 4.

• Z can be S or Cr.

(NH₄)₂Cu(SO₄)₂ • 6H₂O is an example of a Tutton’s salt.

Predict the formula of a Tutton’s salt containing different ions from (NH₄)₂Cu(SO₄)₂ • 6H₂O.

A student prepares a sample of the Tutton’s salt, (NH₄)₂Cu(SO₄)₂ • 6H₂O using the method shown below.

Step 1 Dissolve 0.025 mol of ammonium sulfate and 0.025 mol of hydrated copper(II) sulfate, CuSO₄ • 5H₂O, in water and make up to 50 cm³.

Step 2 Boil the resulting mixture for 2 minutes and allow to cool.

Step 3 Allow the solvent to evaporate slowly. Pale blue crystals of the Tutton’s salt form.

What masses are needed of ammonium sulfate and CuSO₄ • 5H₂O?

mass of ammonium sulfate........ g

mass of CuSO₄ • 5H₂O........ g

In Step 3, why does the student allow the solvent to evaporate and not boil off all the solvent in Step 2 ?

The student dissolves their Tutton’s salt in water. A pale blue solution forms.

The student carries out two tests on this aqueous solution.

The student adds an excess of aqueous ammonia to their aqueous solution of Tutton’s salt. A deep blue solution forms.

The complex ion responsible for the deep blue solution has a molar mass of 167.5 g mol^–1.

Suggest the formula of this complex ion.

The student adds NaOH(aq) to the aqueous solution of Tutton’s salt and warms the mixture.

A precipitate and a gas are formed.

Write the formulae of the precipitate and gas and suggest a test that could confirm the identity of the gas.

Formula of precipitate........

Formula of gas........

Test to confirm the identity of the gas........

How could the student carry out a test-tube test to confirm the anion in the Tutton’s salt?

Aspirin tablets are used for pain relief.

The structure of aspirin is shown below.

A student uses the reaction of aspirin with cold NaOH(aq) to determine the mass of aspirin in one tablet.

In this reaction, 1 mol of aspirin reacts with 1 mol of cold NaOH(aq).

The student’s method is outlined below.

Step 1 The student reacts three aspirin tablets with 100 cm³ of 0.500 mol dm^–3 NaOH(aq). The NaOH is in excess. A colourless solution forms.

Step 2 The colourless solution from Step 1 is made up to 250.0 cm³ with distilled water.

Step 3 A 25.00 cm³ sample of the diluted solution from Step 2 is titrated with 0.200 mol dm^–3 HCl(aq) in the burette.

The HC l (aq) reacts with excess NaOH(aq) that remains in Step 1:

The student repeats the titration to obtain concordant (consistent) titres.

Titration results The trial titre has been omitted.

The burette readings have been read to the nearest 0.05 cm³.

Analysis of results From the results, the student can determine the following.

1. The amount, in mol, of excess NaOH(aq) that remains after the reaction of aspirin with NaOH(aq).

2. The amount, in mol, of NaOH(aq) that reacted with the aspirin.

Use the results to determine the mass, in mg, of aspirin in one aspirin tablet.

Aspirin reacts with hot NaOH(aq), under reflux.

Draw a labelled diagram of suitable apparatus for reflux.

In this reaction, 1 mol of aspirin reacts with 3 mol of hot NaOH(aq).

Complete the equation for the reaction of aspirin with an excess of hot NaOH(aq).

Show structures for organic compounds.

This question is about nitric acid, hydrochloric acid and sulfuric acid.

Dilute nitric acid reacts with aluminium oxide to form a solution of aluminium nitrate.

Write an equation for this reaction.

The solution contains nitrate ions, NO₃^–.

Draw a ‘dot-and-cross’ diagram for the NO₃^– ion.

Use a different symbol for the extra electron.

Balance the half-equation for the oxidation process in this reaction.

In the reduction process in this reaction, HNO₃ and H⁺ react together to form 2 oxides: X (M_r = 30) and Z (M_r = 18).

Determine the formulae of X and Z and write the half-equation for this reduction.

* Three reactions involving sulfuric acid are shown below.

Reaction 1 Dilute sulfuric acid is reacted with nickel(II) hydroxide to form a green solution.

The solvent is allowed to evaporate leaving hydrated crystals of compound D, with the percentage composition by mass: Ni, 22.33%; S, 12.20%; O, 60.87%; H, 4.60%.

Reaction 2 Concentrated sulfuric acid is reacted with hydrogen bromide, HBr, to form three products:

• an element which exists as diatomic molecules

• a gaseous compound E

• a liquid.

At RTP, 1.00 dm³ of compound E has a mass of 2.67 g.

Reaction 3 Concentrated sulfuric acid acts as a catalyst when 2-hydroxypropanoic acid reacts to form compound F (M_r = 144).

In this reaction, 2 mol of 2-hydroxypropanoic acid forms 1 mol of compound F and 2 mol of water.

Identify compounds D, E and F and construct equations for the reactions.

Show structures for any organic compounds.