Advanced Inorganic & Organic Chemistry Core Practicals (Edexcel International A Level Chemistry)

Exam Questions

3 hours13 questions

Medium

Hard

1a1 mark

A flowchart of a series of reactions of chromium and some of its compounds is shown.

q1-paper-6-jan-2022-edexcel-ial-chemistry

Give the formula of a complex ion of chromium present in solution A.

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1b1 mark

Give the formula of precipitate B.

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1c1 mark

Identify reagent C, by name or formula.

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1d1 mark

Suggest the identity, by name or formula, of precipitate D.

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1e1 mark

State the colour of solution E.

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1f1 mark

State the colour of solution F.

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2a3 marks

This question is about copper and some of its compounds.

Two tests were carried out on separate samples of an aqueous solution of copper(II) sulfate.

(i) Test 1

A few drops of aqueous sodium hydroxide were added to a sample of the copper(II) sulfate solution.

State what you would see.

(1)

(ii) Test 2

A few drops of concentrated hydrochloric acid were added to another sample of the copper(II) sulfate solution.
More of the concentrated hydrochloric acid was added until it was present in excess.

Describe the changes that would be observed during this test.

(2)

How did you do?

2b2 marks

Describe a test, and its positive result, to confirm the presence of the sulfate ion in another sample of the copper(II) sulfate solution.

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4 marks

An electrochemical cell was made from the electrode systems represented by these half-equations:

Cu²⁺(aq) + 2e^–⇌ Cu(s) $E^{⦵}$ = +0.34V
Fe³⁺(aq) + e⁻⇌ Fe²⁺(aq) $E^{⦵}$ = +0.77V

Calculate

E_{cell}^{⦵}

for the electrochemical cell.

(1)

ii)

A student drew a diagram of an experiment to measure the standard emf of the cell.

q1c-ii-paper-6-oct-2021-edexcel-ial-chemistry

Identify three mistakes in this diagram and the changes needed to correct them.

Assume that standard conditions were used.

(3)

Mistake	Change needed to correct mistake

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8 marks

Brass is an alloy of copper and zinc.
A student determined the percentage of copper in a sample of brass.

Procedure

weigh the sample of brass
place the brass in a beaker and add concentrated nitric acid until all the brass dissolves
transfer the solution and washings to a 250.0 cm³volumetric flask
make the solution up to the mark with distilled water and mix well
pipette 25.0 cm³of the solution into a conical flask
neutralise the excess nitric acid in the solution
add 10 cm³ of potassium iodide solution (an excess) to the conical flask
titrate the iodine produced with 0.100 mol dm⁻³ sodium thiosulfate solution using starch indicator
repeat the titration until concordant titres are obtained.

Copper and zinc both react with concentrated nitric acid to form the metal nitrates, nitrogen dioxide and water.

Write the balanced equation for the reaction of zinc with concentrated nitric acid.
State symbols are not required.

(1)

ii)

Name the most suitable piece of apparatus to measure the 10 cm³ of potassium iodide solution.

(1)

iii)

State at what point in the titration the starch solution should be added.

(1)

iv)

Only Cu²⁺ ions in the solution react with the aqueous potassium iodide.

2Cu²⁺ + 4I^– → 2CuI + I₂

The iodine reacts with sodium thiosulfate solution.

2S₂ $O_{3}^{2 -}$ + I₂ → S₄ $O_{6}^{2 -}$ + 2I^–

Results

Mass of brass sample = 3.90 g

Mean titre of 0.100 mol dm⁻³ sodium thiosulfate solution = 28.60 cm³
Calculate the percentage, by mass, of copper in this sample of brass.

Give your answer to an appropriate number of significant figures.

(5)

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4a3 marks

Two organic compounds, A and B, are colourless liquids.

Each compound contains only one functional group.

Two tests were carried out on A. The observation for each test was recorded in the table.

Complete the statements in the inference column by writing the names or formulae of the functional groups.

(2)

Test	Observation	Inference
Test 1 A few drops of A were added to 2 cm³ of a solution of 2,4-dinitrophenylhydrazine (Brady’s reagent)	An orange precipitate formed	A could contain ........................................ or ........................................
Test 2 A few drops of A were added to 2 cm³ of Fehling’s solution The mixture was warmed in a water bath	A red precipitate formed	The functional group present in A is .........................................

ii)

Give the name or formula of the red precipitate formed in Test 2.

(1)

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4b2 marks

A simplified mass spectrum of A is shown.

q2bi-paper-6-oct-2021-edexcel-ial-chemistry

Give the formula of one of the ions responsible for the peak at m / z = 29.

(1)

ii)

A contains one functional group.
Give the m / z value of the molecular ion and the structure of A.

(1)

m / z value of the molecular ion ..............................................................
structure of A

How did you do?

4c3 marks

Two tests were carried out on B.

Complete the statements in the observation and inference columns.

(2)

Test

Observation

Inference

Test 3

2 drops of B were dissolved in 2 cm³of water

A few drops of Universal Indicator were added to the solution

The colour of the mixture was .............................

The solution is alkaline

Test 4

B was added drop by drop to aqueous copper(II) sulfate until B was present in excess

A pale blue precipitate formed with the first few drops of B

This dissolved to form a deep blue solution when excess B was added

The name of the functional group in B is

...................................

ii)

B has a molar mass of 59 g mol⁻¹.
Suggest a structure for B.

(1)

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5a1 mark

This question concerns the laboratory preparation of tetraamminecopper(II) sulfate-1-water, Cu(NH₃)₄SO₄•H₂O.

Procedure

Step 1	Weigh between 2.1 g and 2.3 g of hydrated copper(II) sulfate, CuSO₄•5H₂O, in a boiling tube. Add 8 cm³ of distilled water and place the boiling tube in a hot water bath. Stir the mixture until the crystals have dissolved.
Step 2	Working in a fume cupboard, slowly pour 5 cm³of concentrated aqueous ammonia into the boiling tube. Stir until a clear solution is obtained.
Step 3	Measure 12 cm³ of ethanol into a 100 cm³ conical flask and add the contents of the boiling tube from Step 2. Stopper the flask and swirl the contents before placing the flask in an ice bath. Allow the mixture to stand until crystals of Cu(NH₃)₄SO₄•H₂O have formed.
Step 4	Filter the crystals obtained in Step 3 under reduced pressure, using a Buchner funnel and flask.
Step 5	Pour 5 cm³ of cold ethanol over the crystals in the funnel.
Step 6	Using a spatula, transfer the crystals to a filter paper on a watch glass. Press a second piece of filter paper on the crystals, to dry them as much as possible.
Step 7	Transfer the crystals to a dry, pre-weighed sample bottle and reweigh.

Give a reason why a measuring cylinder is more suitable than a graduated pipette for measuring the distilled water in Step 1.

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5b1 mark

Give the colour of the solution at the end of Step 2.

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5c1 mark

Give the reason why Step 2 should be carried out in a fume cupboard.

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5d1 mark

Give the reason why the addition of ethanol in Step 3 results in the precipitation of crystals of Cu(NH₃)₄SO₄•H₂O.

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5e3 marks

Draw a labelled diagram of the apparatus used to filter the crystals under reduced pressure in Step 4.

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5f2 marks

State the purpose of the ethanol in Step 5.

(1)

ii)

Give a reason why the ethanol is cold.

(1)

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4 marks

Starting with 2.17 g of CuSO₄•5H₂O and using excess ammonia, a student obtained 2.54 g of product.

Calculate the apparent percentage yield of Cu(NH₃)₄SO₄•H₂O.
Give your answer to an appropriate number of significant figures.

(3)

ii)

Suggest a reason why the apparent percentage yield in this preparation is often greater than 100%.

(1)

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6a4 marks

This question is about the identification of six organic compounds.

q3-paper-6-2021-june-edexcel-ial-chemistry

From A, B, C, D, E and F, identify the compound with

the fewest peaks in its carbon-13 NMR spectrum.

(1)

ii)

the most peaks in its low resolution proton NMR spectrum.

(1)

iii)

three peaks with relative peak area 3:2:3 in its low resolution proton NMR spectrum.

(1)

iv)

one triplet and one quartet as the only peaks in its high resolution proton NMR spectrum.

(1)

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6b4 marks

For each of the following pairs, give one chemical test, not including indicators, that could be used to distinguish the compounds.

Identify the reagents and give the results of each test.

A and B

(2)

ii)

C and D

(2)

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6c4 marks

Liquids boil at the temperature at which their vapour pressure is equal to atmospheric pressure.

The apparatus shown below was used to determine the boiling temperature of compound A, which is a liquid at room temperature and pressure and has a boiling temperature in the range 120°C to 180°C.

q3c-paper-6-2021-june-edexcel-ial-chemistry

Procedure

Step 1	Place a capillary tube, sealed at one end and with the open end facing down, into 0.5 cm³ of compound A in a micro test tube. Attach the micro test tube to a thermometer with a rubber band.
Step 2	Clamp the micro test tube and thermometer in the mineral oil, making sure neither test tube nor thermometer bulb is in contact with the glass walls of the Thiele tube.
Step 3	Move a small Bunsen flame back and forth along the lower part of the side-arm of the Thiele tube. An initial stream of bubbles will come from the open end of the capillary tube.
Step 4	Continue heating until a rapid and continuous stream of bubbles comes from the capillary tube. Stop heating and record the temperature as soon as compound A is drawn up into the capillary tube.

State what causes the initial stream of bubbles from the capillary tube in Step 3.

(1)

ii)

Suggest why the side-arm of the Thiele tube is heated, rather than point X on the diagram.

(1)

iii)

Suggest why mineral oil, and not water, is used in the Thiele tube when determining the boiling temperature of compound A.

(1)

iv)

Suggest why the results obtained when using this apparatus on different days may not be the same, even when no mistakes are made in carrying out the experiment.

(1)

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10 marks

One of the compounds A, B, C, D, E or F was analysed.

To determine its empirical formula, 1.57 g of the compound was burned completely and the combustion products passed through the apparatus shown.

q3d-paper-6-2021-june-edexcel-ial-chemistry
Solid M absorbed water and increased in mass by 1.28 g.

Solid N absorbed carbon dioxide and increased in mass by 3.14 g.

Identify, by name or formula, suitable substances for solids M and N.

(2)

Solid M .......................................................................................................
Solid N ........................................................................................................

ii)

Calculate the empirical formula of the compound, using the data given.
You must show your working.

(4)

iii)

The mass spectrum of the compound is shown.

q3d-iii-paper-6-2021-june-edexcel-ial-chemistry

Deduce the relative molecular mass of the compound, using the mass spectrum.

(1)

iv)

Deduce the molecular formula of the compound, using your answers to (d)(ii) and (d)(iii).

(1)

Determine the identity of the compound, using your answer to (d)(iv) and the fragmentation pattern of the mass spectrum.
Justify your answer.

(2)

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7a6 marks

Azo dyes, such as Organol Brown, can be made from benzene, C₆H₆, using the reaction scheme shown.

Due to the toxicity of benzene, the first step is never carried out in a school laboratory.

q3-paper-6-jan-2021-edexcel-ial-chemistry

In the preparation of nitrobenzene, benzene is added slowly to a mixture of concentrated nitric and sulfuric acids.

The mixture is warmed at 55 °C under reflux for 45 minutes. The reaction mixture is stirred continuously.

State why a reflux condenser is needed when the mixture is warmed.

(1)

ii)

Draw a diagram of the apparatus used to warm under reflux in this experiment.

(3)

iii)

Suggest why the reaction mixture is stirred continuously.

(2)

How did you do?

7b1 mark

The excess acid is removed from the reaction mixture. The layer containing nitrobenzene is separated and dried before being purified by distillation.

Identify a suitable drying agent.

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7c3 marks

Nitrobenzene is then reduced to phenylamine, C₆H₅NH₂.

Phenylamine reacts with nitrous acid at a temperature between 0 °C and 10 °C to form a diazonium compound.

Nitrous acid is formed in the reaction mixture using sodium nitrite and hydrochloric acid.

State why nitrous acid is generated in the reaction mixture instead of being obtained from a chemical supplier.

(1)

ii)

Explain why the temperature of the reaction between phenylamine and nitrous acid must be neither lower than 0 °C nor higher than 10 °C.

(2)

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7d5 marks

Reaction of the diazonium compound with an alkaline solution of naphthalene-1-ol produces the solid azo dye, Organol Brown.
The solid is purified by recrystallisation.

Procedure

Step 1	The impure Organol Brown is dissolved in a minimum volume of hot solvent.
Step 2	The solution is filtered hot through a preheated funnel.
Step 3	The solution is cooled and filtered using a Buchner funnel.
Step 4	The solid is rinsed with a small amount of ice-cold solvent.
Step 5	The solid is dried in a desiccator.

State why a minimum volume of hot solvent is used in Step 1.

(1)

ii)

Explain why a preheated funnel is used in Step 2.

(1)

iii)

Give a reason for each of the two filtrations in Steps 2 and 3.

(2)

iv)

Give a possible reason why it is preferable to dry the solid in a desiccator rather than in an oven in Step 5.

(1)

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7e1 mark

The melting temperature of the recrystallised Organol Brown is measured to check its purity.

State what you would observe if the sample was pure.

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8a2 marks

This question is about the preparation of phenylamine by the reduction of nitrobenzene.

q4-paper-6-jan-2022-edexcel-ial-chemistry

Outline procedure

Step 1	Add 2.1 cm³ of nitrobenzene, 5 g of granulated tin and 10 cm³ of concentrated hydrochloric acid to a round‐bottomed flask.
Step 2	Add a few anti‐bumping granules to the flask and heat the contents under reflux for 15 minutes. Leave to cool.
Step 3	Dissolve 7.5 g of sodium hydroxide in 10 cm³ of distilled water and add to the flask. An initial precipitate forms before redissolving.
Step 4	Add 15 cm³ of distilled water to the flask and steam distil the contents, collecting the cloudy distillate in a conical flask.
Step 5	Add 3 g of powdered sodium chloride to the distillate and swirl to dissolve, before transferring the contents to a separating funnel. Add 8 cm³ of ether to the funnel and shake, occasionally relieving the pressure. Allow the layers to separate.
Step 6	Discard the aqueous layer before transferring the ether layer to a clean flask containing a few pellets of potassium hydroxide.
Step 7	Decant the contents of the flask from Step 6 into a pear‐shaped flask and distil off all the ether.
Step 8	Distil the remaining contents of the pear‐shaped flask, collecting the fraction boiling between 180°C and 185°C.

Some data relating to the organic chemicals involved in the preparation are shown.

Chemical	Hazard	M_r	Density / gcm^–3	Boiling temperature / °C
Nitrobenzene	Toxic by inhalation and skin absorption	123.0	1.20	211
Phenylamine	Toxic by inhalation and skin absorption	93.0	1.03	184
Ether	Highly flammable	74.0	0.71	35

Give two reasons why gloves should be worn in Step 1.

How did you do?

8b2 marks

State the role of tin in the preparation.

(1)

ii)

Suggest, by name or formula, the identity of the initial precipitate formed in Step 3.

(1)

How did you do?

8c1 mark

State why the distillate in Step 4 is cloudy.

How did you do?

8d1 mark

Suggest why sodium chloride is added to the distillate in Step 5.

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8e3 marks

Draw a labelled diagram of the separating funnel at the end of Step 5.

(2)

ii)

State how you would relieve the pressure in the separating funnel in Step 5.

(1)

How did you do?

8f1 mark

Suggest one reason for adding pellets of potassium hydroxide in Step 6.

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8g2 marks

State how the mixture would be heated to distil off the ether in Step 7.
Justify your answer.

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4 marks

Calculate the mass of phenylamine formed in this preparation.

The limiting reagent is nitrobenzene and the overall yield by mass is 43%.

Refer to all the information at the start of the question.

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9a3 marks

This question is about the alkaline hydrolysis of an ester, X.
X is an alkyl benzoate and can be represented by the formula C₆H₅COOR, where R is the alkyl group.
The equation for the hydrolysis is

C₆H₅COOR + NaOH → C₆H₅COONa + ROH

Procedure

Step 1	Measure 5.0 cm³of X and pour it into a pear-shaped flask. Add 25 cm³(an excess) of aqueous sodium hydroxide solution and a few anti-bumping granules.
Step 2	Heat the flask and contents under reflux for 20 minutes.
Step 3	Allow the apparatus to cool and then rearrange it for distillation. Distil the mixture and collect about 2 cm³of the alcohol ROH.
Step 4	Allow the pear-shaped flask to cool, pour the contents into a beaker and add excess dilute hydrochloric acid. Impure benzoic acid forms as crystals in the mixture.
Step 5	Recrystallise the benzoic acid using water as the solvent.
Step 6	Weigh the dry crystals and determine their melting temperature.

A student drew a diagram of the apparatus set up for distillation in Step 3.
There are three errors in the diagram.

Assume the apparatus is clamped correctly and an appropriate heat source is used.

q4ai-paper-6-oct-2021-edexcel-ial-chemistry Identify the three errors and how they should be corrected.

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9b2 marks

The distillate collected in Step 3 is the alcohol ROH.

Describe a chemical test, and its positive result, to show the presence of an –OH group in any alcohol.

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9c2 marks

Write an equation for the reaction taking place in Step 4.
Use structural formulae for the organic substances. State symbols are not required.

(1)

ii)

State what should be done to separate the benzoic acid from the mixture produced in Step 4, before carrying out Step 5.

(1)

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9d1 mark

Describe the first stage in the recrystallisation process in Step 5.

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9e2 marks

The melting temperature of pure benzoic acid is 122°C.

State two ways in which the melting temperature changes if the benzoic acid is not pure.

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5 marks

The molar mass of X, C₆H₅COOR, is 178 g mol⁻¹.

Deduce the formula of the alkyl group, R.

(1)

ii)

Use your answer to (f)(i) to draw the structures of the four possible alcohols, ROH.

(2)

iii)

The part of the ¹³C NMR spectrum of X corresponding to the R group contains only two peaks.
Deduce the structure of X.

(2)

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1a6 marks

This question is about compounds containing the ammonium ion, ${NH}_{4}^{+}$ .

Ammonium vanadate(V), NH₄VO₃, is a white solid.

When excess dilute sulfuric acid is added to an aqueous solution of NH₄VO₃, the

{VO}_{3}^{-}

ion is converted into the

{VO}_{2}^{+}

ion.
Write the ionic equation for the conversion of

{VO}_{3}^{-}

{VO}_{2}^{+}

on the addition of dilute sulfuric acid. State symbols are not required.

(1)

ii)

State the colour of an acidified solution of ammonium vanadate(V).

(1)

iii)

A student added zinc metal to an acidified solution of ammonium vanadate(V).
The zinc reduced the vanadium in a series of reactions.

The student suggested that the sequence of colours observed could be explained by the presence of the vanadium species shown in the table.

Sequence of colours observed	starting colour $\to$ green $\to$ blue $\to$ green $\to$ violet
Suggested vanadium species	${VO}_{2}^{+} \to$ V³⁺ $\to$ VO²⁺ $\to$ V³⁺ $\to$ V²⁺

Explain whether or not the student is correct.
Refer to oxidation states of vanadium and account for each colour in the sequence.

(2)

iv)

When the mixture obtained at the end of the sequence in (a)(iii) is filtered, the filtrate changes colour from violet to green on standing. No further changes occur.

Suggest an explanation for these observations.

(2)

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1b6 marks

Ammonium tetrachlorocuprate(II) dihydrate, (NH₄)₂CuCl₄•2H₂O, is a blue-green solid.

When ammonium tetrachlorocuprate(II) dihydrate is dissolved in water, a blue-green solution T is formed.

Suggest the formulae of two complex ions present in solution T.

(2)

ii)

State how the colour of solution T would change on the addition of excess concentrated hydrochloric acid.

(1)

iii)

Describe what would be observed on the addition of aqueous sodium hydroxide to solution T.

(1)

iv)

When the mixture from (b)(iii) is warmed, a gas is evolved.
Give a test to identify the gas stating the positive result of the test.

(2)

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1c3 marks

A white solid with a slight vinegar-like smell contains ammonium ions, ${NH}_{4}^{+}$ , and an anion represented by Y⁻ .

The smell of vinegar intensifies on the addition of a few drops of concentrated sulfuric acid to an aqueous solution of NH₄Y.

On subsequent addition of a few drops of ethanol and heating the mixture, the smell of vinegar is replaced by a sweet and fruity smell.

Explain how all this information can be used to identify the anion Y⁻.

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1 mark

This question is about the identification of three organic compounds, X, Y and Z.

A molecule of each compound has only one type of functional group.
Each compound contains six carbon atoms and two oxygen atoms.

In the mass spectrum of X, the molecular ion peak is at m/ z = 114.

State the molecular formula of X.

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2b3 marks

Three chemical tests are carried out on X.

Test 1	When Brady’s reagent (2,4‐dinitrophenylhydrazine solution) is added to X, an orange precipitate is observed
Test 2	When X is heated with an acidified solution of potassium dichromate(VI), no change is observed.
Test 3	When X is added to an alkaline solution of iodine, the formation of a pale yellow precipitate is observed.

Explain what can be deduced about the functional group present in X, by considering the results of each of these tests.

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2c2 marks

The high resolution proton NMR spectrum of X contains only two singlets with relative peak areas of 3:2.

Draw the structure of X, identifying the two proton environments.

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2d5 marks

The molecular formula of Y is C₆H₁₂O₂.

When aqueous sodium carbonate is added to Y, effervescence is observed.
Identify, by name or formula, the functional group present in Y.

(1)

ii)

The ¹³C NMR spectrum of Y contains four peaks.
Give two possible structures for Y.

(2)

Structure 1	Structure 2

iii)

Explain how the low resolution proton NMR spectrum of Y would confirm which of your structures in (d)(ii) is correct.
Chemical shifts are not required.

(2)

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2e5 marks

The molecular formula of Z is C₆H₁₂O₂.

The infrared spectrum of Z is shown.

q2e-paper-6-jan-2022-edexcel-ial-chemistry

Group	Wavenumber range / cm^–1
C $-$ H stretching vibrations
Alkane	2962–2853
Alkene	3095–3010
Aldehyde	2900–2820 and 2775–2700
O $-$ H stretching vibrations
Alcohols	3750–3200
Carboxylic acids	3300–2500
C $=$ O stretching vibrations
Aldehydes	1740–1720
Ketones	1720–1700
Carboxylic acids	1725–1700
Esters	1750–1735

Z has a fruity smell.

Deduce the identity of the functional group present in Z, using all the information given.
Include any relevant wavenumber ranges in your answer.

(2)

ii)

The high resolution proton NMR spectrum of Z contains four peaks (J, K, L and M). Peak J has the highest chemical shift, showing that this proton environment is close to an electronegative atom.

The splitting pattern of the peaks is shown.

Peak	J	K	L	M
Splitting pattern	septet	quartet	doublet	triplet

Draw the displayed structure of Z, labelling the proton environment responsible for each of the peaks J, K, L and M.

(3)

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3a2 marks

Students were told to determine the concentration of a solution of potassium chlorate(V), KClO₃. Two methods were used: precipitation and titration.

Method 1 – Precipitation

Step 1	Bubble excess sulfur dioxide, SO₂, into 100 cm³ of the potassium chlorate(V) solution.
Step 2	Boil the resulting mixture to remove excess SO₂ and then add silver nitrate solution until no more silver chloride precipitate forms.
Step 3	Filter, dry and weigh the precipitate.

The equation for the reaction in Step 1 is shown.

${ClO}_{3}^{-} (aq) + 3 {SO}_{2} (g) + 3 H_{2} O (l) \to {Cl}^{-} (aq) + 6 H^{+} (aq) + 3 {SO}_{4}^{2 -} (aq)$

Identify the main hazard in Step 1, giving a safety precaution that will reduce the risk.
Assume that safety spectacles and a laboratory coat were used.

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2 marks

The reaction in Step 2 produced 0.430 g of a white precipitate of silver chloride, AgCl.

Calculate the concentration of KClO₃ in the solution, in mol dm^–3, found using Method 1.
You must show your working.

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3c2 marks

A student who used Method 1 obtained a value that was significantly larger than the actual concentration of the solution.

Explain one possible source of experimental error which might lead to this result.

How did you do?

3d1 mark

Method 2 – Titration

Step 1	Mix a sample of potassium chlorate(V) solution with an acidified solution containing iron(II) sulfate, FeSO₄
Step 2	Remove the chloride ions produced in Step 1.
Step 3	Determine the concentration of excess iron(II) ions by titrating the whole of the solution with a standard solution of potassium manganate(VII).

The equation for the reaction in Step 1 is shown.

${ClO}_{3}^{-} (aq) + 6 {Fe}^{2 +} (aq) + 6 H^{+} (aq) \to {Cl}^{-} (aq) + 6 {Fe}^{3 +} (aq) + 3 H_{2} O (l)$

Give the colour change observed in Step 1.

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3e5 marks

Describe how to carry out the titration in Step 3. You should identify suitable apparatus and any additional chemicals required.

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6 marks

In Method 2, 50.0 cm³ of potassium chlorate(V) was mixed with 150 cm³ of 0.0750 mol dm^–3 of iron(II) sulfate. The iron (II) sulfate was in excess.

The whole of this solution required 9.25 cm³ of 0.050 mol dm^–3of potassium manganate(VII) to completely react.

The equations for the reactions are

${ClO}_{3}^{-} (aq) + 6 {Fe}^{2 +} (aq) + 6 H^{+} (aq) \to {Cl}^{-} (aq) + 6 {Fe}^{3 +} (aq) + 3 H_{2} O (l) {MnO}_{4}^{-} (aq) + 5 {Fe}^{2 +} (aq) + 8 H^{+} (aq) \to {Mn}^{2 +} (aq) + 5 {Fe}^{3 +} (aq) + 4 H_{2} O (l)$

Calculate the concentration, in mol dm^–3, of the potassium chlorate(V) solution.
You must show your working.

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3g2 marks

Explain the change, if any, to the value calculated in (f) if the chloride ions were not removed before the reaction in Step 3 of Method 2.

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