OCR A Level Chemistry A Unified chemistry June 2022 question paper H432/03

These questions are from different areas of chemistry.

Ammonia, NH₃, and ammonium nitrate, NH₄NO₃, are compounds of nitrogen.

The boiling point of NH₃ is –33 °C.

The boiling point of NH₄NO₃ is 210 °C.

Explain why there is a large difference in boiling points.

Two students discuss the oxidation numbers in ammonium nitrate, NH₄NO₃.

One student claims that the two nitrogen atoms have the same oxidation number. The other student disagrees and claims that the nitrogen atoms have different oxidation numbers.

Explain with reasons which student is correct.

What are the percentage compositions of copper and zinc in the brass sample?

Calculate the relative atomic mass of zinc in the sample of brass.

Give your answer to 2 decimal places.

Fill in the table to predict the splitting patterns in the proton NMR spectrum of the

The table shows the chemical shifts for the peaks in the proton NMR spectrum at proton environments 2 and 3.

Proton environment	2	3
Chemical shift,	2.5 ppm	3.6 ppm

Suggest why the peaks for proton environments 2 and 3 have the chemical shifts which are shown in the table.

Glycine, H₂NCH₂COOH, is an -amino acid.

Glycine reacts with NaOH to form the salt H₂NCH₂COONa.

Glycine reacts with HCl to form the salt HOOCCH₂NH₃Cl.

The salts have different H–N–H bond angles.

State the different H–N–H bond angles and explain why they are different.

H₂NCH₂COONa H–N–H bond angle =........ °

HOOCCH₂NH₃Cl H–N–H bond angle =........ °

Glycine reacts with aqueous copper(II) ethanoate to form copper(II) glycinate, Cu(H₂NCH₂COO)₂, and ethanoic acid. Copper(II) glycinate is a complex which exists as two square planar isomers.

Write an equation for this reaction and draw the structures of the two square planar isomers of the complex Cu(H₂NCH₂COO)₂.

equation

This question is about redox reactions.

‘Calcium hypochlorite’, Ca(Cl O)₂, is an ionic compound used in ‘bleaching powder’.

The Cl O^– ion in Ca(Cl O)₂ is the active ingredient that kills bacteria.

Calcium hypochlorite is prepared by reacting chlorine gas with calcium hydroxide.

A student analyses the redox reactions shown below. State symbols have been omitted.

The student concludes that different ions containing chromium can act as oxidising or reducing agents.

Using the terms oxidising agent and reducing agent, and ideas about electrode potentials and equilibrium, explain how the student is correct.

Include overall equations.

A student bubbles hydrogen sulfide gas, H₂S(g), through an acidified solution containing manganate(VII) ions, MnO₄^–(aq).

A redox reaction takes place, forming aqueous manganese(II) ions, a yellow precipitate and one other product.

Construct the equation for this reaction. State symbols are not required.

Information about 1-bromobutane and butan-1-ol is shown in the table.

A student prepares a sample of 1-bromobutane by refluxing 9.25 g of butan-1-ol with sodium bromide and sulfuric acid.

After reflux, the reaction mixture is purified.

The student obtains 6.10 cm³ of pure 1-bromobutane.

* Draw a diagram to show how the student would have carried out the reflux and calculate the percentage yield of 1-bromobutane that the student obtains.

Describe how the student could have obtained pure 1-bromobutane from the reaction

mixture obtained after reflux.

Butan-1-ol reacts with sodium bromide and sulfuric acid to form 1-bromobutane by nucleophilic substitution.

The mechanism for this reaction takes place by two steps.

Step 1 The oxygen atom of the alcohol group accepts a proton to form a positively-charged intermediate.

Step 2 Bromide ions react with the intermediate from Step 1 by nucleophilic substitution to form 1-bromobutane.

Show both steps in this mechanism.

Two students plan to investigate Equilibrium 4.1, shown below.

The students are supplied with the equilibrium mixture in Equilibrium 4.1 at room temperature.

• One student heats 20 cm³ of the mixture to 50 °C.

• The other student heats 20 cm³ of the mixture to 90 °C.

The students use colorimetry to observe how the colour of the equilibrium mixture changes over time.

• The colorimeter is set up so that the greater the absorbance, the greater the

The students plot the graph below from the results of the experiment.

Use the graph and relevant chemical theory to answer the following. Include all reasoning:

• Explain the different initial rates at 50 °C and 90 °C.

• Predict the sign of ∆ H for the forward reaction in Equilibrium 4.1.

The students investigate how addition of aqueous silver nitrate, AgNO₃(aq), affects the equilibrium position in Equilibrium 4.1.

The graph shows the changes in the equilibrium concentrations of CoCl₄^2–, Cl^– and [Co(H₂O)₆]²⁺ after addition of the AgNO₃(aq).

The AgNO₃(aq) is added at time = t₁.

Explain why the Cl^– concentration drops sharply at time = t₁.

This question is about energy changes.

* A student plans to determine the enthalpy change of hydration of calcium ions.

The student finds the information below from data tables.

The student carries out an experiment to find the enthalpy change of solution of calcium chloride.

Student’s method:

• Weigh a bottle containing calcium chloride and weigh a polystyrene cup.

• Add water from a measuring cylinder to the polystyrene cup and measure its temperature.

• Add the calcium chloride, stir the mixture, and measure the maximum temperature of the final solution.

• Weigh the empty bottle and weigh the polystyrene cup with the final solution.

Mass readings

Temperature readings

Calculate the enthalpy change of solution of calcium chloride and determine the enthalpy change of hydration of calcium ions.

Show your working, including an energy cycle linking the energy changes.

Assume that the density and specific heat capacity, c, of the solution are the same as for

water.

Internal combustion engines have historically used fuels obtained from crude oil as a source of power.

The environmental effects of fossil fuel use can be reduced by blending petrol with biofuels such as ethanol.

A fuel is being developed using a 1:1 molar ratio of octane and ethanol.

Write the equation for the complete combustion of this fuel.

Calculate the energy released, in kJ, by the complete combustion of 8.00 kg of this fuel.

_cH(C₈H₁₈) = –5470 kJ mol^–1; ∆_cH(C₂H₅OH) = –1367 kJ mol^–1.

A student carries out an investigation on vitamin C, C₆H₈O₆.

Vitamin C is extremely soluble in water. This means that vitamin C is removed rapidly from the body. ‘Vitamin C ester’ is available in tablet form as a less soluble source of vitamin C which stays in the body for longer.

Suggest why vitamin C is extremely soluble in water.

A ‘vitamin C ester’ tablet contains an ester with the molecular formula C₂₂H₃₈O₇.

This ester can be prepared by reacting vitamin C with a long chain carboxylic acid, C_xH_yCOOH, in the presence of an acid catalyst.

Vitamin C and the long chain carboxylic acid react in a 1:1 molar ratio.

Determine x and y in the formula of this carboxylic acid.

Vitamin C, C₆H₈O₆, is a weak acid (K_a = 7.94 x 10^–5 (mol dm^–3)), which is often referred to as ascorbic acid.

The label on a carton of orange juice lists the mass of vitamin C, in mg, in a typical serving of 150 cm³.

The student carries out an investigation to check the vitamin C content in the orange juice.

Vitamin C can be oxidised by iodine:

The student dilutes 150 cm³ of the orange juice with water to 250.0 cm³ in a volumetric flask.

The student then titrates 25.0 cm³ volume of this solution with 9.60 × 10^–4 mol dm^–3 iodine solution, I₂(aq).

The mean titre of I₂(aq) is 22.50 cm³.

Determine the mass, in mg, of vitamin C in a 150 cm³ serving of the orange juice.