this question is about nitrobenzenes

This question is about nitrobenzenes.

(a) Nitrobenzene reacts when heated with a mixture of concentrated nitric acid andconcentrated sulfuric acid to form a mixture of three isomeric dinitrobenzenes.

Write an equation for the reaction of concentrated nitric acid with concentrated sulfuric acidto form the species that reacts with nitrobenzene.

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(1)

1

(b) Name and outline a mechanism for the reaction of this species with nitrobenzene to form1,3-dinitrobenzene.

Name of mechanism____________________________________________________________

Mechanism

(4)

of 96Catalyst Tutors

(c) The dinitrobenzenes shown were investigated by thin layer chromatography (TLC).

In an experiment, carried out in a fume cupboard, a concentrated solution of pure1,4-dinitrobenzene was spotted on a TLC plate coated with a solid that contains polarbonds. Hexane was used as the solvent in a beaker with a lid.

The start line, drawn in pencil, the final position of the spot and the final solvent frontare shown on the chromatogram in the diagram below

Use the chromatogram in the diagram above to deduce the Rf value of 1,4-dinitrobenzenein this experiment.

Tick (✔) one box.

A 0.41

B 0.46

C 0.52

D 0.62

(1)


(d) State in general terms what determines the distance travelled by a spot in TLC.

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(1)

(e) To obtain the chromatogram, the TLC plate was held by the edges and placed in thesolvent in the beaker in the fume cupboard. The lid was then replaced on the beaker.

Give one other practical requirement when placing the plate in the beaker.

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(1)

(f) A second TLC experiment was carried out using 1,2‑dinitrobenzene and1,4‑dinitrobenzene. An identical plate to that in part (c) was used under the sameconditions with the same solvent. In this experiment, the Rf value of 1,4‑dinitrobenzenewas found to be greater than that of 1,2‑dinitrobenzene.

Deduce the relative polarities of the 1,2‑dinitrobenzene and 1,4‑dinitrobenzene and explainwhy 1,4‑dinitrobenzene has the greater Rf value.

Relative polarities

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Explanation

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(2)


(g) A third TLC experiment was carried out using 1,2‑dinitrobenzene. An identical plate to thatin part (c) was used under the same conditions, but the solvent used contained a mixture ofhexane and ethyl ethanoate.

A student stated that the Rf value of 1,2‑dinitrobenzene in this third experiment would be

greater than that of 1,2‑dinitrobenzene in the experiment in part (f)

Is the student correct? Justify your answer.

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(2)

(Total 12 marks)

1,4-diaminobenzene is an important intermediate in the production of polymers such as Kevlarand also of polyurethanes, used in making foam seating.

A possible synthesis of 1,4-diaminobenzene from phenylamine is shown in the following figure.

2


(a) A suitable reagent for step 1 is CH3COCl

Name and draw a mechanism for the reaction in step 1.

Name of mechanism __________________________________________________

Mechanism

(5)

(b) The product of step 1 was purified by recrystallisation as follows.

The crude product was dissolved in the minimum quantity of hot water and the hotsolution was filtered through a hot filter funnel into a conical flask. This filtration removedany insoluble impurities. The flask was left to cool to room temperature.The crystals formed were filtered off using a Buchner funnel and a clean cork was used tocompress the crystals in the funnel. A little cold water was then poured through thecrystals.After a few minutes, the crystals were removed from the funnel and weighed.A small sample was then used to find the melting point.

Give reasons for each of the following practical steps.

The minimum quantity of hot water was used

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The flask was cooled to room temperature before the crystals were filtered off

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The crystals were compressed in the funnel

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A little cold water was poured through the crystals

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(4)

(c) The melting point of the sample in part (b) was found to be slightly lower than a data-bookvalue.

Suggest the most likely impurity to have caused this low value and an improvement to themethod so that a more accurate value for the melting point would be obtained.

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(2)

The figure above is repeated here to help you answer the following questions.


(d) In an experiment starting with 5.05 g of phenylamine, 4.82 g of purified product wereobtained in step 1.

Calculate the percentage yield in this reaction.Give your answer to the appropriate number of significant figures.

Percentage yield = _______________%

(3)

(e) A reagent for step 2 is a mixture of concentrated nitric acid and concentrated sulfuric acid,which react together to form a reactive intermediate.

Write an equation for the reaction of this intermediate in step 2.

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(1)

(f) Name a mechanism for the reaction in step 2.

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(1)

(g) Suggest the type of reaction occurring in step 3.

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(1)

(h) Identify the reagents used in step 4.

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(1)

(Total 18 marks)


The infrared spectrum (Figure 1) and the 1H NMR spectrum (Figure 2) of compound R withmolecular formula C6H14O are shown.

Figure 1

3

Figure 2


The relative integration values for the NMR peaks are shown on Figure 2.

Deduce the structure of compound R by analysing Figure 1 and Figure 2.Explain each stage in your deductions.

Use Table A and Table B on the Data Sheet.

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(Total 8 marks)

A peptide is hydrolysed to form a solution containing a mixture of amino acids. This mixture isthen analysed by silica gel thin-layer chromatography (TLC) using a toxic solvent. The individualamino acids are identified from their Rf values.

Part of the practical procedure is given below.

1. Wearing plastic gloves to hold a TLC plate, draw a pencil line 1.5 cm from the bottom ofthe plate.

2. Use a capillary tube to apply a very small drop of the solution of amino acids to themid-point of the pencil line.

3. Allow the spot to dry completely.4. In the developing tank, add the developing solvent to a depth of not more than 1 cm.5. Place your TLC plate in the developing tank.6. Allow the developing solvent to rise up the plate to the top.7. Remove the plate and quickly mark the position of the solvent front with a pencil.8. Allow the plate to dry in a fume cupboard.

4


(a) Parts of the procedure are in bold text.

For each of these parts, consider whether it is essential and justify your answer.

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(4)

(b) Outline the steps needed to locate the positions of the amino acids on the TLC plate and todetermine their Rf values.

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(4)

(c) Explain why different amino acids have different Rf values.

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(2)

(Total 10 marks)


Compound R contains 61.0% carbon and 11.9% hydrogen by mass. The remainder is oxygen.The mass spectrum of R contains a molecular ion peak at m/z = 118.

(a) Use these data to show that the molecular formula of R is C6H14O2.

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(3)

5

(b) The infrared spectrum of R (C6H14O2) is shown below.

The proton n.m.r. spectrum of R contains five peaks. The chemical shift values, integrationratios and splitting patterns of these peaks are given in the table.

Chemical shift/ppm 3.8 3.2 3.1 1.4 1.1

Integration ratio 2 3 1 2 6

Splitting patterns triplet singlet singlet triplet singlet

When R is warmed with acidified potassium dichromate(VI) a green solution is formed.

Use Table A and Table B on the data sheet and all of the data provided in the question todeduce the structure of R.

In your answer, explain how you have used the data provided in the question.

(9)

(Total 12 marks)


A green solution, X, is thought to contain [Fe(H2O)6]2+ ions.

(a) The presence of these ions can be confirmed by reacting separate samples of solution Xwith aqueous ammonia and with aqueous sodium carbonate.

Write equations for each of these reactions and describe what you would observe.

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(4)

6

(b) A 50.0 cm3 sample of solution X was added to 50 cm3 of dilute sulfuric acid and made up to250 cm3 of solution in a volumetric flask.

A 25.0 cm3 sample of this solution from the volumetric flask was titrated with a 0.0205 moldm−3 solution of KMnO4

At the end point of the reaction, the volume of KMnO4 solution added was 18.70 cm3.

(i) State the colour change that occurs at the end point of this titration and give a reasonfor the colour change.

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(2)


(ii) Write an equation for the reaction between iron(II) ions and manganate(VII) ions.

Use this equation and the information given to calculate the concentration of iron(II)ions in the original solution X.

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(5)

(Total 11 marks)


N-phenylethanamide is used as an inhibitor in hydrogen peroxide decomposition and also in theproduction of dyes.

N-phenylethanamide can be produced in a laboratory by the reaction between phenylammoniumsulfate and an excess of ethanoic anhydride:

(a) A student carried out this preparation using 1.15 g of phenylammonium sulfate (Mr = 284.1)and excess ethanoic anhydride.

(i) Calculate the maximum theoretical yield of N−phenylethanamide that could beproduced in the reaction. Record your answer to an appropriate precision.

Show your working.

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(3)

7

(ii) In the preparation, the student produced 0.89 g of N−phenylethanamide.

Calculate the percentage yield for the reaction.

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(1)


(b) The student purified the crude solid product, N−phenylethanamide, by recrystallisation.

(i) Outline the method that the student should use for this recrystallisation.

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(4)

(ii) Outline how you would carry out a simple laboratory process to show that therecrystallised product is a pure sample of N−phenylethanamide.

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(3)


(iii) Assume that the reaction goes to completion.

Suggest two practical reasons why the percentage yield for this reaction may not be100%.

1. ____________________________________________________________

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2. ____________________________________________________________

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(2)

(c) The reaction to form N−phenylethanamide would happen much more quickly if the studentused ethanoyl chloride instead of ethanoic anhydride.

Explain why the student might prefer to use ethanoic anhydride, even though it has aslower rate of reaction.

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(2)

(Total 15 marks)


(a) Sodium hydroxide can be obtained as a monohydrate (NaOH.H2O). When heated, thewater of crystallisation is lost, leaving anhydrous sodium hydroxide (NaOH).

A chemist weighed a clean, dry crucible. The chemist transferred 1.10 g of NaOH.H2O tothe crucible. The crucible and its contents were heated until a constant mass had beenreached. The chemist recorded this mass.

The experiment was repeated using different masses of the monohydrate.

For each experiment, the chemist recorded the original mass of NaOH.H2O and the massof NaOH left after heating. The chemist’s results are shown in the table below.

Mass of NaOH.H2O / g Mass of NaOH / g

0.50 0.48

1.10 0.79

2.05 1.41

2.95 2.06

3.50 2.28

4.20 2.93

4.90 3.41

8


(i) Plot a graph of mass of NaOH.H2O (y-axis) against mass of NaOH on the grid.Draw a straight line of best fit on the graph.

(3)


(ii) Use your graph to determine the mass of NaOH.H2O needed to form 1.00 g of NaOH

_____________ g

(1)

(iii) Use your answer from part (a) (ii) to confirm that the formula of sodium hydroxidemonohydrate is NaOH.H2O

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(2)

(b) Sodium hydroxide is used to remove grease from metal components.Sodium hydroxide cannot be used to clean components made of aluminium because itreacts with this metal.

(i) Balance the equation for the reaction of aqueous sodium hydroxide with aluminium.

...... NaOH + ...... Al + ...... H2O ...... NaAl(OH)4 + 3H2

(1)

(ii) In 1986, a sealed aluminium tank exploded while being used by mistake fortransporting concentrated sodium hydroxide solution.

Suggest one reason why the tank exploded.

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(1)

(c) A strong alkali such as potassium hydroxide is used as the electrolyte in some alkalinebatteries for household use. The electrolyte will escape if the battery casing is broken.

Suggest one reason why a leak of this electrolyte is hazardous.

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(1)

(Total 9 marks)


(a) Ester 1 and Ester 2 were studied by 1H n.m.r. spectroscopy.

Ester 1 Ester 2

One of the two esters produced this spectrum.

ppm

Deduce which of the two esters produced the spectrum shown. In your answer, explain theposition and splitting of the quartet peak at δ = 4.1 ppm in the spectrum.

9

Predict the δ value of the quartet peak in the spectrum of the other ester.

Use Table B on the Data Sheet.

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(4)


(b) Cetrimide is used as an antiseptic.

[CH3(CH2)15N(CH3)3]+ Br–

cetrimide

Name this type of compound.

Give the reagent that must be added to CH3(CH2)15NH2 to make cetrimide and state thereaction conditions.

Name the type of mechanism involved in this reaction.

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(4)

(c) Give a reagent that could be used in a test-tube reaction to distinguish between benzeneand cyclohexene.Describe what you would see when the reagent is added to each compound and the testtube is shaken.

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(3)

(Total 11 marks)


In an experiment to determine the acid dissociation constant (Ka) of a weak acid, 25.0 cm3 of an

approximately 0.1 mol dm–3 solution of this acid were titrated with a0.10 mol dm–3 solution of sodium hydroxide.The pH was measured at intervals and recorded. The table below shows the results.

Volume of NaOH / cm3 0.0 1.0 2.0 3.0 4.0 5.0 10.0 15.0

pH 5.1 7.8 8.1 8.7 8.4 8.5 8.9 9.3

Volume of NaOH / cm3 20.0 22.0 23.0 24.0 25.0 26.0 27.0 28.0

pH 9.7 10.0 10.2 11.0 11.3 11.4 11.5 11.6

10


(a) On the grid below, plot the values from the table above on a graph of pH (y-axis) againstvolume of NaOH.

You should start your y-axis at pH 4.0.Draw a curve that represents the curve of best fit through these points. Ignore anyanomalous points.


(4)

(b) Deduce the volume of the sodium hydroxide solution that would have been added at thehalf-neutralisation point of this experiment. This is the point where half the amount of theweak acid has been neutralised.

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(1)

(c) When half of the weak acid has been neutralised, the pH of the mixture at this point isequal to the pKa of the weak acid.

Use your answer to part (b) and your graph to determine the pKa of the weak acid and,hence, its Ka value.

pKa _______________________________________________________________

Ka ________________________________________________________________

(2)

(d) State the pH value for the anomalous point on your graph.Suggest one reason for this anomaly. Assume that the reading on the pH meter is correct.

pH ________________________________________________________________

Reason for anomaly __________________________________________________

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(1)

(e) Suggest how the experimental procedure could be slightly modified in order to give a morereliable value for the end-point.

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(1)

(Total 9 marks)


Chlorine can be found in water. One method for the determination of chlorine in water is to usecolorimetry.

A colourless sample of water from a vase of flowers was analysed after the addition of compoundZ as the addition of Z resulted in a purple solution.

Compound W

(a) Calculate the Mr of Compound W.

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(1)

11

(b) Determine the percentage, by mass, of nitrogen in this compound.

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(1)

(c) A simplified diagram of a colorimeter is shown below.


(i) Suggest why it is important that the container for each sample has the samedimensions.

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(1)

(ii) Suggest why the coloured filter is used.

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(1)

(iii) Suggest one reason why a colorimetric method might be chosen in preference totitration.

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(1)

(Total 5 marks)

A biocide is a chemical that kills bacteria. A biocide is added to prevent the growth of bacteria inthe water used in vases of flowers. Household bleach contains aqueous chlorine and can beused as the biocide. The concentration of chlorine in vase water decreases with time. It wasdecided to investigate the rate of this decrease.

The following experimental method was used to determine the concentration of chlorine in vasewater at different times.

• A sample of vase water was taken.• An excess of potassium iodide solution was added to the sample.• The chlorine in the sample oxidised the I − ions to I2• The iodine was titrated with sodium thiosulfate (Na 2S2O3) solution.• These steps were repeated using further samples taken from the vase water at hourly

intervals.

(a) Suggest two reasons why the concentration of chlorine in the vase water decreases withtime.

Reason 1 ___________________________________________________________

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Reason 2 ___________________________________________________________

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(2)

12


(b) Suggest why this sampling technique has no effect on the rate at which the concentrationof chlorine in the vase water decreases.

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(1)

(c) Why was it important to use an excess of potassium iodide solution?

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(1)

(d) Use the following standard electrode potential data to explain why I2 oxidises S2O32− under

standard conditions.

+ e− I− = +0.54 V

+ e− S2O32− = +0.09 V

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(1)

(e) Deduce an ionic equation for the reaction between I2 and S2O32−

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(1)

(Total 6 marks)

A 5.00 g sample of potassium chloride was added to 50.0 g of water initially at 20.0 °C. Themixture was stirred and as the potassium chloride dissolved, the temperature of the solutiondecreased.

13


(a) Describe the steps you would take to determine an accurate minimum temperature that isnot influenced by heat from the surroundings.

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(4)

(b) The temperature of the water decreased to 14.6 °C.

Calculate a value, in kJ mol−1, for the enthalpy of solution of potassium chloride.

You should assume that only the 50.0 g of water changes in temperature and that thespecific heat capacity of water is 4.18 J K−1 g−1.Give your answer to the appropriate number of significant figures.

Enthalpy of solution = _______________ kJ mol−1

(4)


(c) The enthalpy of solution of calcium chloride is −82.9 kJ mol−1.The enthalpies of hydration for calcium ions and chloride ions are −1650 and−364 kJ mol−1, respectively.

Use these values to calculate a value for the lattice enthalpy of dissociation of calciumchloride.

Lattice enthalpy of dissociation = _______________ kJ mol−1

(2)

(d) Explain why your answer to part (c) is different from the lattice enthalpy of dissociation formagnesium chloride.

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(2)

(Total 12 marks)


The following tests were carried out to identify an unknown green salt Y.

An aqueous solution of Y gave a cream precipitate of compound A when reacted with silvernitrate solution.

Compound A gave a colourless solution when reacted with concentrated ammonia solution.

Another aqueous solution of Y gave a green precipitate B when reacted with sodium carbonatesolution.

The green precipitate B was filtered and dried and then reacted with sulfuric acid to give a palegreen solution containing compound C and a colourless gas D.

(a) Identify by name or formula the compounds A, B, C, D and Y.

Identity of A _________________________________________________________

Identity of B _________________________________________________________

Identity of C _________________________________________________________

Identity of D _________________________________________________________

Identity of Y _________________________________________________________

(5)

14

(b) Write the simplest ionic equation for the reaction of silver nitrate solution with the anion thatis present in compound Y.

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(1)

(c) Write the simplest ionic equation for the reaction that occurs between the green precipitateB and sulfuric acid.

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(1)

(Total 7 marks)


Ethanol can be oxidised by acidified potassium dichromate(VI) to ethanoic acid in a two-stepprocess.

ethanol ethanal ethanoic acid

(a) In order to ensure that the oxidation to ethanoic acid is complete, the reaction is carried outunder reflux.

Describe what happens when a reaction mixture is refluxed and why it is necessary, in thiscase, for complete oxidation to ethanoic acid.

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(3)

15

(b) Write a half-equation for the overall oxidation of ethanol into ethanoic acid.

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(1)


(c) The boiling points of the organic compounds in a reaction mixture are shown in thefollowing table.

Compound ethanol ethanal ethanoic acid

Boiling point / °C 78 21 118

Use these data to describe how you would obtain a sample of ethanal from a mixture ofthese three compounds. Include in your answer a description of the apparatus you woulduse and how you would minimise the loss of ethanal. Your description of the apparatus canbe either a description in words or a labelled sketch.

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(5)

(d) Use your knowledge of structure and bonding to explain why it is possible to separateethanal in this way.

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(2)


(e) A student obtained a sample of a liquid using the apparatus in part (c).

Describe how the student could use chemical tests to confirm that the liquid containedethanal and did not contain ethanoic acid.

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(5)

(Total 16 marks)

When iodine molecules are dissolved in aqueous solutions containing iodide ions, they react toform triiodide ions (I3–).

I2 + I– I3–

The rate of the oxidation of iodide ions to iodine by peroxodisulfate(VI) ions (S2O82–) was studied

by measuring the concentration of the l3– ions at different times, starting at time = 0, when the

reactants were mixed together. The concentration of the l3– ions was determined by measuringthe absorption of light using a spectrometer.

The table below shows the results.

Time / s Concentration of l3– / mol dm–3

10 0.23

20 0.34

30 0.39

40 0.42

50 0.47

60 0.44

70 0.45

16


(a) Plot the values of the concentration of I3– (y-axis) against time on the grid below.

(2)

(b) A graph of these results should include an additional point. On the grid, draw a ring aroundthis additional point.

(1)


(c) Draw a best-fit curve on the grid, including the extra point from part (b).

(2)

(d) Draw a tangent to your curve at time = 30 seconds. Calculate the slope (gradient) of thistangent and hence the rate of reaction at 30 seconds. Include units with your final answer.Show your working.

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(4)

(Total 9 marks)

The triiodomethane reaction is often used as a test for aldehydes and ketones that contain theCH3CO group shown.

The aldehyde or ketone is reacted with an alkaline solution of iodine. Triiodomethane (CHl3) isformed as a precipitate. Compounds that contain a group that can be oxidised to the CH3COgroup will also give a positive result in this test.

17

(a) State, with a reason, whether or not ethanol will give a positive result in the triiodomethanereaction.

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(1)


(b) The equation for the reaction of ethanal with an alkaline solution of iodine is

CH3CHO + 3l2 + 4NaOH CHl3 + HCOONa + 3Nal + 3H2O

In an experiment using this reaction, the yield of triiodomethane (CHl3) obtained by astudent was 83.2%.

Calculate the minimum mass of iodine that this student would have used to form 10.0 g oftriiodomethane.Give your answer to the appropriate precision.Show your working.

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(5)

(c) Triiodomethane can be separated from the reaction mixture by filtration.State one reason why the solid residue is then washed with water after the filtration.

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(1)

(d) State one reason, other than cost or availability, why water is suitable for washing this solidresidue after the filtration.

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(1)

(Total 8 marks)


In order to obtain a pH curve, you are provided with a conical flask containing 25.0 cm3 of a0.100 mol dm–3 carboxylic acid solution and a burette filled with 0.100 mol dm–3 sodiumhydroxide solution. You are also provided with a calibrated pH meter.

(a) State why calibrating a pH meter just before it is used improves the accuracy of the pHmeasurement.

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(1)

18

(b) Describe how you would obtain the pH curve for the titration.

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(5)

(Total 6 marks)


(a) A chemist discovered four unlabelled bottles of liquid, each of which contained a differentpure organic compound. The compounds were known to be propan-1-ol, propanal,propanoic acid and 1-chloropropane.

Describe four different test-tube reactions, one for each compound, that could be used toidentify the four organic compounds.Your answer should include the name of the organic compound, the reagent(s) used andthe expected observation for each test.

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19

(Extra space) ________________________________________________________

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(8)

(b) A fifth bottle was discovered labelled propan-2-ol. The chemist showed, using infraredspectroscopy, that the propan-2-ol was contaminated with propanone.

The chemist separated the two compounds using column chromatography. The columncontained silica gel, a polar stationary phase.


The contaminated propan-2-ol was dissolved in hexane and poured into the column.Pure hexane was added slowly to the top of the column. Samples of the eluent (thesolution leaving the bottom of the column) were collected.

• Suggest the chemical process that would cause a sample of propan-2-ol to becomecontaminated with propanone.

• State how the infrared spectrum showed the presence of propanone.

• Suggest why propanone was present in samples of the eluent collected first (thosewith shorter retention times), whereas samples containing propan-2-ol were collectedlater.

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___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(4)

(Total 12 marks)


When 1.00 mol dm–3 solutions of salicylic acid and sodium hydroxide are mixed a buffer solutioncan be formed. Salicylic acid is a monoprotic acid that can be represented by the formula HA.

(a) Select a mixture from the table below that would produce a buffer solution. Give a reasonfor your choice.

MixtureVolume of 1.00 mol dm–3

salicylic acid solution / cm3

Volume of 1.00 mol dm–3

sodium hydroxide solution / cm3

X 25 75

Y 50 50

Z 75 25

Mixture ____________________________________________________________

Reason ____________________________________________________________

___________________________________________________________________

___________________________________________________________________

(2)

20

(b) Another mixture, formed by adding 50 cm3 of 1.00 mol dm–3 salicylic acid solution to 25cm3 of 1.00 mol dm–3 sodium hydroxide solution, can be used to determine the pKa ofsalicylic acid. State one measurement that must be made for this mixture and explain howthis measurement can be used to determine the pKa of salicylic acid.

Measurement _______________________________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

(3)

(Total 5 marks)


Salicylic acid can be used to make aspirin. Before using a sample of salicylic acid to makeaspirin, a student purified the acid by recrystallisation. The method for recrystallisation is outlinedbelow.

Step 1: The sample is dissolved in a minimum volume of hot water.Step 2: The solution is filtered hot.Step 3: The filtrate is cooled in ice to form crystals.Step 4: The crystals are collected by filtration, washed with cold water and left to dry.

Explain the purpose of each underlined point.

Minimum volume _________________________________________________________

_______________________________________________________________________

Hot water_______________________________________________________________

_______________________________________________________________________

Filtered hot______________________________________________________________

_______________________________________________________________________

Cooled in ice ____________________________________________________________

_______________________________________________________________________

Washed with cold water ____________________________________________________

_______________________________________________________________________

(Total 5 marks)

21


Titration curves labelled A, B, C and D for combinations of different aqueous solutions of acidsand bases are shown below.All solutions have a concentration of 0.1 mol dm–3.

22

(a) In this part of the question write the appropriate letter in each box.

From the curves A, B, C and D, choose the curve produced by the addition of

ammonia to 25 cm3 of hydrochloric acid

sodium hydroxide to 25 cm3 of ethanoic acid

nitric acid to 25 cm3 of potassium hydroxide

(3)


(b) A table of acid.base indicators is shown below.The pH ranges over which the indicators change colour and their colours in acid and alkaliare also shown.

Indicator pH range Colour in acid Colour in alkali

Trapaeolin 1.3 – 3.0 red yellow

Bromocresol green 3.8 – 5.4 yellow blue

Cresol purple 7.6 – 9.2 yellow purple

Alizarin yellow 10.1 – 12.0 yellow orange

(i) Select from the table an indicator that could be used in the titration that producescurve B but not in the titration that produces curve A.

______________________________________________________________

(1)

(ii) Give the colour change at the end point of the titration that produces curve D whencresol purple is used as the indicator.

______________________________________________________________

(1)

(Total 5 marks)


Organic chemists use a variety of methods to distinguish between compounds. These methodsinclude analytical and spectroscopic techniques.

(a) The following compounds can be distinguished by observing what happens in test-tubereactions.

For each pair, suggest a suitable reagent or reagents that could be added separately toeach compound in order to distinguish them.

Describe what you would observe with each compound.

(i)

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(3)

23

(ii)

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(3)


(iii)

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(3)

(b) Compounds J and K can also be distinguished using spectroscopic techniquessuch as 1H n.m.r.

(i) Name compound J.

Give the total number of peaks in the 1H n.m.r. spectrum of J.

State the splitting pattern, if any, of the peak for the protons labelled a.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(3)


(ii) Name compound K.

Give the total number of peaks in the 1H n.m.r. spectrum of K.

State the splitting pattern, if any, of the peak for the protons labelled b.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(3)

(Total 15 marks)

(a) Propanoic acid can be made from propan-1-ol by oxidation using acidified potassiumdichromate(VI). Propanal is formed as an intermediate during this oxidation.

(i) State the colour of the chromium species after the potassium dichromate(VI) hasreacted.

______________________________________________________________

(1)

24

(ii) Describe the experimental conditions and the practical method used to ensure thatthe acid is obtained in a high yield. Draw a diagram of the assembled apparatus youwould use.

Conditions _____________________________________________________

______________________________________________________________

Apparatus

(4)

(iii) Describe the different experimental conditions necessary to produce propanal in highyield rather than propanoic acid.

______________________________________________________________

______________________________________________________________

(2)

(b) Propan-1-ol is a volatile, flammable liquid.Give one safety precaution that should be used during the reaction to minimise this hazard.

___________________________________________________________________

(1)


(c) A student followed the progress of the oxidation of propan-1-ol to propanoic acid byextracting the organic compounds from one sample of reaction mixture.

(i) Give a chemical reagent which would enable the student to confirm the presence ofpropanal in the extracted compounds.State what you would observe when propanal reacts with this reagent.

Reagent _______________________________________________________

Observation ____________________________________________________

______________________________________________________________

(2)

(ii) Give a chemical reagent that would enable the student to confirm the presence ofpropanoic acid in the extracted compounds.State what you would observe when propanoic acid reacts with this reagent.

Reagent _______________________________________________________

Observation ____________________________________________________

______________________________________________________________

(2)

(d) Predict which one of the compounds, propan-1-ol, propanal and propanoic acid will havethe highest boiling point. Explain your answer.

Prediction __________________________________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(3)

(Total 15 marks)


Samples of 1-chloropropane and ethanoyl chloride can be distinguished by the addition of anaqueous solution of silver nitrate.State what you would observe with each sample.

Observation with 1-chloropropane

_______________________________________________________________________

_______________________________________________________________________

Observation with ethanoyl chloride.

_______________________________________________________________________

_______________________________________________________________________

(Total 2 marks)

25

The compound (CH3CH2)2NH can be made from ethene in a three-step synthesis as shownbelow.

(a) Name the compound (CH3CH2)2NH

___________________________________________________________________

(1)

26

(b) Identify compounds F and G.

Compound F ________________________________________________________

Compound G ________________________________________________________

(2)


(c) For the reactions in Steps 1, 2 and 3,

• give a reagent or reagents• name the mechanism.

Balanced equations and mechanisms using curly arrows are not required.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(6)

(d) Identify one organic impurity in the product of Step 3 and give a reason for its formation.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(2)

(Total 11 marks)


Ethanoic acid is manufactured in industry from methanol and carbon monoxide in a multi-stepprocess involving hydrogen iodide. Ethanoic acid is obtained from the reaction mixture byfractional distillation. Methanoic acid is a useful by-product of this process.

The Ka value of an organic acid can be determined by using the pH curve obtained when the

acid is titrated against sodium hydroxide. The pH of the solution formed when exactly half of theacid has been neutralised is equal to the pKa value of the acid. The Ka value of the acid can be

used to confirm its identity.

A chemist used a pH curve to determine the pKa value of acid Y, formed during the manufacture

of ethanoic acid. The chemist transferred 25.0 cm3 of a solution of acid Y into a beaker using apipette, and measured the pH of the acid solution using a pH meter which could be read to onedecimal place. A solution of sodium hydroxide of concentration 0.100 mol dm–3 was added froma burette in small portions. The pH of the mixture was recorded after each addition of the sodiumhydroxide solution. The chemist’s results are given in the table below.

Volume of sodiumhydroxide solution

added / cm3pH

Volume of sodiumhydroxide solution

added / cm3pH

0.0 3.0 23.5 5.1

2.0 3.4 24.0 5.5

4.0 3.5 24.5 11.8

8.0 3.7 25.0 12.1

12.0 4.3 26.0 12.3

16.0 4.1 27.0 12.4

20.0 4.3 28.0 12.5

22.0 4.7 30.0 12.5

27


(a) Use the results given in the table above to plot a graph of pH (y-axis) against volume ofsodium hydroxide solution added. Use the points to draw the pH curve, ignoring anyanomalous results.

(6)


(b) Use your graph from part (a) to determine the

(i) volume of sodium hydroxide solution at the end-point of the titration

__________ cm3

(ii) volume of sodium hydroxide solution needed to neutralise half the acid

__________ cm3

(iii) pH of the half-neutralised mixture. Give your answer to one decimal place.

____________________

(3)

(c) Use the pH of the half-neutralised mixture from part (b) (iii) to calculate the value of the aciddissociation constant, Ka, of the acid Y. Show your working.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(2)

(d) The table below shows the Ka values for some organic acids.

Acid Ka / mol dm–3

Methanoic acid 1.6 × 10–4

Ethanoic acid 1.7 × 10–5

Iodoethanoic acid 6.8 × 10–4

Propanoic acid 1.3 × 10–5

Use your answer from part (c) to identify acid Y from this table.

___________________________________________________________________

(1)


(e) For the pipette and the burette, the maximum total errors are shown below. These errorstake into account multiple measurements.

pipetteburette

± 0.05 cm3

± 0.15 cm3

Estimate the percentage error in using each of these pieces of apparatus. You should useyour answer to part (b) (i) to estimate the percentage error in using the burette.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(1)

(f) Calculate the difference between the Ka value from part (c) and the Ka value of the acid

you identified as the acid Y in the table in part (d).

Express this difference as a percentage of the value given in the table in part (d). (If youcould not complete the calculation in part (c), you should assume that the Ka value

determined from the graph is 1.9 × 10–4 mol dm–3. This is not the correct value.)

___________________________________________________________________

___________________________________________________________________

(1)

(g) Other than by using a different pH meter, state one way in which the accuracy of the pHreadings could be improved.

___________________________________________________________________

___________________________________________________________________

(1)

(h) State why there was little change in the pH value of the mixture when between 8 cm3 and20 cm3 of alkali were added.

___________________________________________________________________

(1)

(Total 16 marks)


Hydrogen peroxide is a powerful oxidising agent. Acidified hydrogen peroxide reacts with iodideions to form iodine according to the following equation.

H2O2(aq) + 2H+(aq) + 2I−(aq) → I2(aq) + 2H2O(l)

The initial rate of this reaction is investigated by measuring the time taken to produce sufficientiodine to give a blue colour with starch solution.

A series of experiments was carried out, in which the concentration of iodide ions was varied,while keeping the concentrations of all of the other reagents the same. In each experiment thetime taken (t) for the reaction mixture to turn blue was recorded.

The initial rate of the reaction can be represented as ( ), and the initial concentration of iodideions can be represented by the volume of potassium iodide solution used.

A graph of log10 ( ) on the y-axis against log10 (volume of KI(aq)) is a straight line. The gradientof this straight line is equal to the order of the reaction with respect to iodide ions.

The results obtained are given in the table below. The time taken for each mixture to turn bluewas recorded on a stopclock graduated in seconds.

Expt.Volume of

KI(aq) / cm3

log10 (volume ofKI(aq)) Time / s log10 ( )

1 5 0.70 71 −1.85

2 8 0.90 46 −1.66

3 10 1.00 37 −1.57

4 15 1.18 25 −1.40

5 20 1.30 19 −1.28

6 25 1.40 14 −1.15

28


(a) Use the results given in the table to plot a graph of log10 ( ) on the y-axis against log10

(volume of KI(aq)).

Draw a straight line of best fit on the graph, ignoring any anomalous points.

(5)


(b) Determine the gradient of the line you have drawn. Give your answer to two decimalplaces. Show your working.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(3)

(c) Deduce the order of reaction with respect to iodide ions.

___________________________________________________________________

(1)

(d) A student carried out the experiment using a flask on the laboratory bench. Thestudent recorded the time taken for the reaction mixture to turn blue. State one waythis method could be improved, other than by repeating the experiment or byimproving the precision of time or volume measurements. Explain why the accuracyof the experiment would be improved.

Improvement ________________________________________________________

___________________________________________________________________

Explanation _________________________________________________________

___________________________________________________________________

(2)

(Total 11 marks)

Describe briefly how you would ensure that a reading from a pH meter is accurate.

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

(Total 2 marks)

29

Salicylic acid, C6H4(OH)COOH, reacts with magnesium to produce magnesium salicylate andhydrogen.

(a) Complete the equation for this reaction.

C6H4(OH)COOH

(1)

30


(b) In an alternative method for determining percentage purity, a student reacted a solution ofsalicylic acid with an excess of magnesium and collected the hydrogen gas that wasreleased.

Complete the diagram below to show an apparatus that could be used to collect andmeasure the volume of hydrogen gas produced.

(1)

(Total 2 marks)

Ammonium chloride, when dissolved in water, can act as a weak acid as shown by the followingequation.

NH4+(aq) NH3(aq) + H+(aq)

The following figure shows a graph of data obtained by a student when a solution of sodiumhydroxide was added to a solution of ammonium chloride. The pH of the reaction mixture wasmeasured initially and after each addition of the sodium hydroxide solution.

31


(a) Suggest a suitable piece of apparatus that could be used to measure out the sodiumhydroxide solution.Explain why this apparatus is more suitable than a pipette for this purpose.

Apparatus__________________________________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

(2)

(b) Use information from the curve in the figure above to explain why the end point of thisreaction would be difficult to judge accurately using an indicator.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(2)

(c) The pH at the end point of this reaction is 11.8.

Use this pH value and the ionic product of water, Kw = 1.0 × 10−14 mol2 dm−6, to calculatethe concentration of hydroxide ions at the end point of the reaction.

Concentration = _______________ mol dm−3

(3)


(d) The expression for the acid dissociation constant for aqueous ammonium ions is

The initial concentration of the ammonium chloride solution was 2.00 mol dm−3.

Use the pH of this solution, before any sodium hydroxide had been added, to calculate avalue for Ka

Ka = _______________ mol dm−3

(3)

(e) A solution contains equal concentrations of ammonia and ammonium ions.

Use your value of Ka from part (d) to calculate the pH of this solution. Explain your working.

(If you were unable to calculate a value for Ka you may assume that it has the value

4.75 × 10−9 mol dm−3. This is not the correct value.)

pH = _______________

(2)

(Total 12 marks)


(a) Write an equation for the reaction that occurs when magnesium is heated in steam.Describe what you would observe when this reaction occurs.

Equation ___________________________________________________________

Observations ________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(3)

32

(b) Write an equation for the reaction that occurs when sodium is heated in oxygen.Describe what you would observe when this reaction occurs.

Equation ___________________________________________________________

Observations ________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(3)

(Total 6 marks)


Mark schemes

(a) HNO3 + 2H2SO4 → NO2+ + H3O+ + 2HSO4

−

Allow H2SO4 + HNO3 → NO2+ + HSO4

− + H2O

Allow a combination of equations which produce NO2+

Penalise equations which produce SO42−

1

1

(b) Electrophilic substitution.

Ignore nitration1

3

OR Kekule

M1 Arrow from inside hexagon to N or + on N (Allow NO2+)

M2 Structure of intermediate

• horseshoe centred on C1 and must not extend beyond C2 andC6, but can be smaller

• + in intermediate not too close to C1 (allow on or “below” aline from C2 to C6)

M3 Arrow from bond into hexagon (Unless Kekule)

• Allow M3 arrow independent of M2 structure• + on H in intermediate loses M2 not M3

(c) D1

(d) (Balance between) solubility in moving phase and retention by stationary phase

OR (relative) affinity for stationary / solid and mobile / liquid /solvent (phase)


(e) Solvent depth must be below start line

Ignore safety1

(f) 1,2- is more polar OR 1,4- is less polarOR 1,2 is polar, 1,4- is non-polar

1

1,4- ( or Less/non polar is) less attracted to (polar) plate / stationary phase / solidOR (Less/non polar is) more attracted to / more soluble in (non-polar) solvent / mobilephase / hexane

1

M2 dependent on correct M1

If M1 is blank then read explanation for possible M1 and M2

Allow converse argument for 1,2

(g) No CE = 0

Yes - mark on but there is NO MARK FOR YES

Mark independently following yes

Solvent (more) polar or ethyl ethanoate is polar1

Polar isomer more attracted to / more soluble in / stronger affinity to the solvent (thanbefore)

Penalise bonded to mobile phase in M21

[12]

(a) (nucleophilic) addition-elimination

Not electrophilic addition-elimination1

2


Allow C6H5 or benzene ring

Allow attack by :NH2C6H5

M2 not allowed independent of M1, but allow M1 for correct attackon C+

M3 for correct structure with charges but lone pair on O is part ofM4

M4 (for three arrows and lone pair) can be shown in more than onestructure

4

(b) The minimum quantity of hot water was used:

To ensure the hot solution would be saturated / crystals would form on cooling1

The flask was left to cool before crystals were filtered off:

Yield lower if warm / solubility higher if warm1

The crystals were compressed in the funnel:

Air passes through the sample not just round it

Allow better drying but not water squeezed out1

A little cold water was poured through the crystals:

To wash away soluble impurities1

(c) Water

Do not allow unreacted reagents1

Press the sample of crystals between filter papers

Allow give the sample time to dry in air1

(d) Mr product = 135.01


Expected mass = 5.05 × = 7.33 g1

Percentage yield = × 100 = 65.75 = 65.8(%)

Answer must be given to this precision

(e)

OR

C6H5NHCOCH3 + NO2+ C6H4(NHCOCH3)NO2 + H+

1

(f) Electrophilic substitution1

(g) Hydrolysis1

(h) Sn / HCl

Ignore acid concentration; allow Fe / HCl1

[18]

IR

Extended response

Absorption at 3360 cm–1 shows OH alcohol present

Deduction of correct structure without explanation scores maximumof 4 marks as this does not show a clear, coherent line ofreasoning.

M11

3

NMR

There are 4 peaks which indicates 4 different environments of hydrogen

Maximum of 6 marks if no structure given OR if coherent logic notdisplayed in the explanations of how two of OH, CH3 and CH2CH3

are identified.M2

1


The integration ratio = 1.6 : 0.4 : 1.2 : 2.4

The simplest whole number ratio is 4 : 1 : 3 : 6M3

1

The singlet (integ 1) must be caused by H in OH alcoholM4

1

The singlet (integ 3) must be due to a CH3 group with no adjacent HM5

1

Quartet + triplet suggest CH2CH3 groupM6

1

Integration 4 and integration 6 indicates two equivalent CH2CH3 groupsM7

1

M8

1

[8]

(a) Wear plastic gloves:

Essential – to prevent contamination from the hands to the plate1

4

Add developing solvent to a depth of not more than 1 cm3:

Essential – if the solvent is too deep it will dissolve the mixture from the plate1

Allow the solvent to rise up the plate to the top:

Not essential – the Rf value can be calculated if the solvent front does not reach thetop of the plate

1

Allow the plate to dry in a fume cupboard:

Essential – the solvent is toxic

Allow hazardous1

(b) Spray with developing agent or use UV1


Measure distances from initial pencil line to the spots (x)1

Measure distance from initial pencil line to solvent front line (y)1

Rf value = x / y1

(c) Amino acids have different polarities1

Therefore, have different retention on the stationary phase or different solubility in thedeveloping solvent

1

[10]

(a) Method 1

M1 %O = 27.1

M2 3 7 1

M3 C3H7O = 59 which is half of Mr so MF = 2EF

OR

Method 2

M1 61% of 118 = 72.0 and 11.9% of 118 = 14.0

M2 72 + 14 = 86 so oxygen = 32 out of 118

OR 27.1% of 118 = 32.0

M3

Method 3

Alternative using given molecular formula

3

5


(b) For this question, marks can be awarded either for a description ofhow the structure is derived or from the given structure itself. Themaximum mark to be awarded is nine from the ten marks listed.

Marks fall into three sections:

• Infrared evidence : two marks are available for use of the infrared evidence, (M1 andM10)

• Chemical evidence: one mark is available for use of the chemical evidence (M2)

• N.m.r. evidence: six marks are available for use of the n.m.r. evidence (M3 – M8inclusive)

plus one mark (M9) for a completely correct structure.

Suggested procedure for marking

First look at the infrared spectrum: marks M1 and M10 may be scored there or in thewritten answer.

Then look for use of the acidified potassium dichromate(VI) evidence, (M2).

Then look at the final structure: this may lead to the award of marks M3 to M9 as shown onthe structures below.

Beware contradictions, e.g. using the chemical evidence they may state that R is a primaryor secondary alcohol but then draw a tertiary alcohol. This will lose M2 but may score M3.

The written ‘evidence’ frequently simply contains extracts from the Table B on the DataSheet and, if only this is given, is unlikely to score many marks.

Described

Or drawn

M1 Infared peak/absorbance at 3400 (cm-1) = O-H alcohol(reference to ir spectrum needed)

Note: please check the spectrum

If peak at 3000 (cm-1) is identified as acid then cannot score M1(contradiction)

M10 Either no peak between 1680-1750 (cm-1) so no C=O or not aldehyde/acidOR peak at 1000-1300 (cm-1) so C–O present

Apply list principle to IR analysis for M10

M2 (Acidified potassium dichromate(VI) turns green) so primary alcohol or secondaryalcohol or not tertiary alcohol

Ignore aldehyde here

Lose M2 if just tertiary alcohol in structure

M3 δ = 3.1 singlet or integration = 1 is O-HAward M3 if structure has 1 O-H group only (can be primary,


secondary or tertiary)

Lose M3 if more than one OH group shown

M4 two triplets at 1.4 & 3.8 = –CH2–CH2–

Allow –CH2–CH2–CH2–

M5 δ = 3.8 means CH2 attached to O (in ether NOT ester)

Allow O–CH2–CH2–CH2–C

δ = 1.4 means CH2 attached to C (but not to C=O)

M6 δ = 1.1 (singlet) integration 6 = 2 × equivalent CH3 on same C

–C(CH3)2–

M7 δ = 1.1 singlet so no H attached to –C(CH3)2-

R–C(CH3)2–R

M8 δ = 3.2 singlet integration 3 = -OCH3

–OCH3

M9 For completely correct

If no structure given then Max 8

R is

This close alternative

would not score M9, but could score up to 8 marks[12]


(a) [Fe(H2O)6]2+ + 2NH3 → Fe(H2O)4(OH)2 + 2NH4+

Allow equation with OH− provided equation showing formation ofOH− from NH3 given

1

Green precipitate1

[Fe(H2O)6]2+ + CO32− → FeCO3 + 6H2O

1

Green precipitate

effervescence incorrect so loses M41

6

(b) (i) Colourless / (pale) green changes to pink / purple (solution)

Do not allow pale pink to purple1

Just after the end−point MnO4− is in excess / present

1

(ii) MnO4− + 8H+ + 5Fe2+ → Mn2+ + 4H2O + 5Fe3+

1

Moles KMnO4 = 18.7 × 0.0205 / 1000 = (3.8335 × 10−4)

Process mark1

Moles Fe2+ = 5 × 3.8335 × 10−4 = 1.91675 × 10−3

Mark for M2 × 51

Moles Fe2+ in 250 cm3 = 10 × 1.91675 × 10−3 = 0.0191675 moles in 50 cm3

Process mark for moles of iron in titration (M3) × 101

Original conc Fe2+ = 0.0191675 × 1000 / 50 = 0.383 mol dm−3

Answer for moles of iron (M4) × 1000 / 50

Answer must be to at least 2 sig. figs. (0.38)1

[11]


(a) (i) Mr N−phenylethanamide = 135.01

Theoretical yield = 135.0 × 2 (1.15 / 284.1) = 1.09 g1

Answer recorded to 3 significant figures.1

(ii) × 100

= 81.4 %

Mark consequentially to (a)Allow 81 to 82

1

7

(b) (i) Dissolve the product in the minimum volume of water / solvent (in a boilingtube / beaker)

If dissolving is not mentioned, CE = 0 / 41

Hot water / solvent

Steps must be in a logical order to score all 4 marks1

Allow the solution to cool and allow crystals to form.1

Filter off the pure product under reduced pressure / using a Buchner funnel andside arm flask

Ignore source of vacuum for filtration (electric pump, water pump,etc.)

1

(ii) Measure the melting point1

Use of melting point apparatus or oil bath1

Sharp melting point / melting point matches data source value1

(iii) Any two from:Product left in the beaker or glasswareSample was still wetSample lost during recrystallisation.

Do not allow “sample lost” without clarification.2 Max


(c) An identified hazard of ethanoyl chloride

E.g. “Violent reaction”, “harmful”, “reacts violently with water”Do not allow “toxic”, “irritant” (unless linked with HCl gas).

1

HCl gas / fumes released / HCl not released when ethanoic anhydride used1

[15]

(a) (i) Uses sensible scales

Lose this mark if the plotted points do not cover half of the paper.

Lose this mark if the graph plot goes off the squared paper.1

8

Plots all of the points correctly ± one small square1

Draws a best-fit line

Lose this mark if the student’s line includes either of the points at0.5 / 0.48 or 3.5 / 2.28

Lose this mark if the student’s line is doubled or kinked.

Lose this mark if the student’s line does not pass within one smallsquare of the origin, extending the line if necessary.

1

(ii) 1.38 to 1.47

Allow answer in this range only.

Answer must correspond to value from the student’s graph.1

(iii) M1Moles NaOH = 1.00 / 40 andMoles water = (part(b) – 1) / 18

Allow any correct method which uses the answer from part (b).1

M2Ratio NaOH : H2O is close to 1:1

Must compare experimental result with theoretical result to scoreM2.

1

(b) (i) 2NaOH + 2Al + 6H2O → 2NaAl(OH)4 + 3H2

Ignore state symbols.1

(ii) Pressure build-up due to the production of hydrogen / H2 / gas

Ignore references to the flammability / explosive nature ofhydrogen.

1


(c) (Alkali is) corrosive / caustic

Allow ‘(alkali) burns skin’.

Ignore ‘harmful’, ‘dangerous’.

Do not allow ‘toxic’ or ‘irritant’.1

[9]

(a) M1 Ester 1

If Ester 2, can score M3 only.1

9

When marking M2 and M3, check any annotation of structures inthe stem at the top of the page.

1

M2 peak at δ = 4.1 due to

M3 (δ = 4.1 peak is) quartet as adjacent / next to / attached to CH31

M4 Other spectrum quartet at δ = 2.1-2.6 (or value in this range)1

(b) M1 Quaternary (alkyl) ammonium salt / bromide1

M2 CH3Br or bromomethane

Penalise contradictory formula and name.1

M3 Excess ( CH3Br or bromomethane)

Mention of acid eg H2SO4 OR alkali eg NaOH loses both M2 andM3.

1

M4 Nucleophilic substitution

Can only score M3 if reagent correct.

Ignore alcohol or ethanol (conditions) or Temp.1

(c) Bromine

(penalise Br butmark on)

Acidified KMnO4

(Penalise missing acidbut mark on)

Wrong reagent = no marks.

If bromine colour stated it must be red, yellow, orange, brown or anycombination, penalise wrong starting colour.

1


Benzene no reaction / colourremains / no(visible) change

no reaction / colourremains / no (visible)change

Ignore ‘clear’, ‘nothing’.

Allow colour fades slowly.

Allow ‘nvc’ for no visible change.1

cyclohexene (Bromine)decolourised

(Acidified KMnO4)decolourised

1

[11]

(a) Correct orientation of graph (pH on y-axis)1

10

Scale – plotted points cover at least half the grid and y-axis should start at pH 41

All points plotted correctly

+ / – one small square.1

Curve of best fit drawn correctly

Allow some leniency here with a complex graph – it is important thatthe section between pH 8.5 and 9.7 is close to linear.

Lose this mark if the line is pulled towards the anomaly at 3.0 cm3.

Lose this mark if first point at pH 5.1 is treated as an anomaly.

Do not accept doubled lines but allow some slight discontinuitywhere the curve changes direction.

1

(b) 11.6-11.9 (cm3) only

Do not mark consequentially to student’s graph.1

(c) pKa = value of pH related to part (b) M1

Mark consequentially on student’s graph – ideally 9.0-9.1

Do not penalise precision of answer.1

Ka = 10−pKa M2

Ideally 1.0 × 10−9 to 7.9 × 10−10

Ignore precision of answer but lose M2 for 1 significant figure here.1


(d) pH 8.7

Ineffective stirring / swirling of the mixture

Both points needed for this mark.

Do not allow pH 5.1

Do not allow ‘overshooting (at 3 cm 3 addition)’.1

(e) Take more pH readings around the end-point / add smaller volumes of NaOH nearthe end-point

Do not allow ‘use a more accurate / reliable pH meter / probe’.

Do not allow the use of a thermostatted mixture.1

[9]

(a) 164.0

Must be 1 decimal place1

11

(b) 17.1(%) (= 28.0 × 100 / Qa)

Consequential on their (a)

Ignore precision but must be to at least 2 sig fig.

(i.e. accept 17 or 17.07)1

(c) (i) Absorption depends on (proportional to) path length / distance travelledthrough solution

Do not allow size.1

(ii) To select the colour / frequency / wavelength that is (most strongly) absorbed(by the sample)

Allow the filter is chosen to complement the colour of the solution1

(iii) Quicker to analyse extracted samples than by titration / uses smaller volumes ofsolution

1

[5]

(a) (Biocide) reacts with bacteria / used up killing bacteria

Max two marks

Chlorine given off / evaporates

Do not allow “chlorine has reacted with water” alone.

Chlorine has reacted with water to form (HCl and) O2

Do not allow products of HCl and HOCl alone2

12


(b) the concentration of the remaining solution (after a sample has been removed) isunchanged.

1

(c) So that all chlorine was reacted / reduced

Do not allow ‘all of the iodide was oxidised’1

(d) The Eo value for the iodine half-equation is more positive than that for the thiosulfate

Allow = 0.45

Must refer to values1

(e) S2O32− + I2 I− + S4O6

2−

Allow multiples1

[6]

(a) Start a clock when KCl is added to water113

Record the temperature every subsequent minute for about 5 minutes

Allow record the temperature at regular time intervals untilsome time after all the solid has dissolved for M2

1

Plot a graph of temperature vs time1

Extrapolate back to time of mixing = 0 and determine the temperature1

(b) Heat taken in = m × c × ΔT = 50 × 4.18 × 5.4 = 1128.6 J

Max 2 if 14.6 °C used as ΔT1

Moles of KCl = 5.00 / 74.6 = 0.06701

Enthalpy change per mole = +1128.6 / 0.0670 = 16 839 J mol-1

1

= +16.8 (kJ mol-1)

Answer must be given to this precision1

(c) ΔHsolution = ΔHlattice + ΔH(hydration of calcium ions) + 2 × ΔH(hydration of chlorideions)

ΔHlattice = ΔHsolution – ΔH(hydration of calcium ions) –2 ×ΔH(hydration of chlorideions)

1


ΔHlattice = –82–9 – (–1650 + 2 × –364) = +2295 (kJ mol–1)1

(d) Magnesium ion is smaller than the calcium ion1

Therefore, it attracts the chloride ion more strongly / stronger ionic bonding1

[12]

(a) A Silver bromide / AgBr1

B Iron(II) carbonate / FeCO31

C Iron(II) sulphate / FeSO41

D Carbon dioxide / CO21

Y Iron(II) bromide / FeBr21

14

(b) Ag+ + Br− ⟶ AgBr

Allow equation if state symbols missing but penalise if statesymbols are incorrect

1

(c) 2H+ + CO32− ⟶ H2O + CO2

Allow FeCO3 + 2H+ ⟶ Fe2+ + CO2 + H2O1

[7]

(a) A mixture of liquids is heated to boiling point for a prolonged time115

Vapour is formed which escapes from the liquid mixture, is changed back into liquidand returned to the liquid mixture

1

Any ethanal and ethanol that initially evaporates can then be oxidised1

(b) CH3CH2OH + H2O CH3COOH + 4H+ + 4e–

1

(c) Mixture heated in a suitable flask / container

A labelled sketch illustrating these points scores the marks1

With still head containing a thermometer1


Water cooled condenser connected to the still head and suitable cooled collectingvessel

1

Collect sample at the boiling point of ethanal1

Cooled collection vessel necessary to reduce evaporation of ethanal1

(d) Hydrogen bonding in ethanol and ethanoic acid or no hydrogen bonding in ethanal1

Intermolecular forces / dipole-dipole are weaker than hydrogen bonding1

(e) Reagent to confirm the presence of ethanal:

Add Tollens’ reagent / ammoniacal silver nitrate / aqueous silver nitrate followed by 1drop of aqueous sodium hydroxide, then enough aqueous ammonia to dissolve theprecipitate formed

OR

Add Fehling’s solution1

Warm

M2 and M3 can only be awarded if M1 is given correctly1

Result with Tollen’s reagent:

Silver mirror / black precipitate

OR

Result with Fehling’s solution:

Red precipitate / orange-red precipitate1

Reagent to confirm the absence of ethanoic acid

Add sodium hydrogencarbonate or sodium carbonate1


Result; no effervescence observed; hence no acid present1

M5 can only be awarded if M4 is given correctly

OR

Reagent; add ethanol and concentrated sulfuric acid and warm

Result; no sweet smell / no oily drops on the surface of the liquid,

hence no acid present

[16]

(a) Sensible scales

Plotted points (including 0,0) must cover more than half the graphpaper.

If axis wrong way round lose this mark but mark on consequentially.

Do not allow broken axis.1

16

Plots points correctly1

(b) Ring around the origin1

(c) Line through points is smooth

Line must pass within ± 1 small square of each plotted point exceptthe anomaly (allow one plot ± 2 small square – at 40 or 60s).

1

Line through points is best fit and ignores anomaly (allow one plot ± 2 small square)

Lose this mark if student’s line is doubled.

Kinked line loses this mark.

Lose this mark if the line does not pass through the origin + / – 1small square.

Lose this mark if the line deviates to anomaly.1

(d) Draws suitable tangent

Must touch the curve at 30s and must not cross the curve.

Lose this mark if the tangent is unsuitable but mark on.1


Chooses appropriate x and y values from their graph

Mark consequentially if axes plotted the wrong way around.

Allow information clearly shown on graph.1

Correctly calculates y / x

Difference in x values and y values must be at least 10 smallsquares in either direction.

1

Gives answer with correct units (mol dm–3 s–1) or correct variant

Lose this mark if answer not to minimum of 2 significant figures andno units or incorrect units are given.

If student has used axis the wrong way round, the unit mark can beawarded for either the correct unit based on their graph or for thecorrect unit for rate.

1

[9]

(a) Yes, because it is oxidised to ethanal / CH3CHOOR it is oxidised to a compound that contains CH3CO group

Ignore ‘primary alcohols are oxidised to aldehydes’.

Need ‘yes’ and an explanation to be awarded the mark.1

17

(b) Mr CHI3 = 393.7 (M1)

Allow if clearly shown in a calculation.

Allow 3941

Moles CHI3 = 10 / 393.7 = 2.54 × 10−2 (M2)

Allow a consequential answer on an incorrect Mr.

2.54 × 10−2 scores M1 and M2.1

Moles I2 = 7.62 × 10−2 (M3)

Allow 3 × M2.1

Mass I2 = 7.62 × 10−2 × 253.8 = 19.34g (M4)

Allow M3 × 253.8 or M3 × 2541


Scaling 19.34 / 0.832 = 23.2g (M5)

Allow M4 / 0.832

Lose this mark if the answer is not given to 3 significant figures.

Answer without working scores M5 only.

Allow any chemically correct alternative method.

Calculations which combine several steps in one expression canscore the marks for all of these individual steps.

1

(c) Remove soluble impurities

Allow ‘remove excess sodium hydroxide / iodine’.

Allow ‘remove excess sodium methanoate / sodium iodide’.

Allow ‘remove excess reagents’.1

(d) Will not dissolve solid / solid is insoluble in water

Allow ‘will not react with solid’.1

[8]

(a) Over time / after storage meter does not give accurate readings

Do not allow ‘to get an accurate reading’ or ‘reading drifts’ on itsown.

Allow ‘temperature variations affect readings’.1

18

(b) Any five from:

Ignore references to the use of the pipette, the filling of the buretteand the calibration of the pH meter.

• Measure pH (of the acid)• Add alkali in known small portions

Allow 1 – 2cm3.• Stir mixture• Measure pH (after each addition)• Repeat until alkali in excess

Allow 27 – 50cm3.• Add in smaller increments near endpoint

Allow 0.1 – 0.5cm3.

To score full marks, the sequence must follow a logical order.5 max

[6]


(a) If 2 stage test for one compound, award no marks for that compound, eg no mark forROH or RX to alkene then Br2 test. If reagent is wrong or missing, no mark for thattest; if wrong but close/incomplete, lose reagent mark but can award for correctobservation. In each test, penalise each example of wrong chemistry, eg AgClr2

propan-1-ol

acidifiedpotassiumdichromate

sodium

Named acid + conc H2SO4

named acyl chloride

PCl5

M11

19

(orange) turns green

effervescence

Sweet smell

Sweet smell /misty fumes

Misty fumes

M21

propanal

add Tollens or Fehlings / Benedicts

acidifiedpotassiumdichromate

Bradys or 2,4-dnph

if dichromate used for alcohol cannot be used for aldehyde

M31


Tollens: silver mirror or Fehlings/ Benedicts: red ppt

(orange) turns green

Yellow or orange ppt

M41

propanoic acid

Named carbonate/ hydrogencarbonate

water and UI (paper)

Named alcohol + conc H2SO4

sodium or magnesium

PCl5if sodium used for alcohol cannot be used for acid

M51

effervescence

orange/red

Sweet smell

effervescence

Misty fumes

if PCl5 used for alcohol cannot be used for acid

M61

1-chloro propane

NaOH then acidified AgNO3

AgNO3

If acidification missed after NaOH,no mark here but allow mark for observation

M71


white ppt

white ppt

M81

(b) oxidation (of alcohol by oxygen in air)

M11

absorption at 1680 -1750 (due to C=O)

Must refer to the spectrum

M21

comparison of polarity of molecules or correct imf statement:propanone is less polar OR propan-2-ol is more polarOR propanone has dipole-dipole forcesOR propan-2-ol has hydrogen bonding

M31

about attraction to stationary phase or solubility in moving phasePropan-2-ol has greater affinity for stationary phase or vice versaOR propanone is more soluble in solvent/moving phase or vice versa

M41

[12]

(a) Z

Mark independently.1

20

The idea that the solution contains both HA and A−

1

(b) pH1

[HA] = [A−]

Accept solution half neutralised.1

pH = pKa

Accept [H+] = Ka1

[5]


Minimum volume and hot water:

Note that this question is worth a total of 5 marks.

Any two from:

to obtain saturated solution

to increase yield / reduce amount left in solution

enable crystallisation (on cooling)

Do not allow ‘because acid doesn’t dissolve well in cold water’.Max 2

21

Filtered hot: to remove insoluble impurities / to prevent crystals forming during filtration1

Cooled in ice: to increase amount of crystals that are formed

Do not allow ‘to cool quickly’.1

Washed with cold water: to remove soluble impurities

Allow ‘washing with hot water would dissolve some of the crystals’.1

[5]

(a) C1

A1

D1

22

(b) (i) Bromocresol green

Allow wrong spellings1

(ii) Purple to yellow

Must have both colours:

Purple start – yellow finish1

[5]


(a) (i) Single reagent

If wrong single reagent, CE = zero

Incomplete single reagent (e.g. carbonate) or wrong formula (e.g.NaCO3) losesreagent mark, but mark on

For “no reaction” allow “nothing”

Different reagents

If different tests on E and F; both reagents and any followon chemistry must be correct for first (reagent) mark.Reagent must react: i.e. not allow Tollens on G (ketone) – no reaction.Second and third marks are for correct observations.i.e. for different tests on E and F, if one reagent is correct and one wrong, can scoremax 1 for correct observation with correct reagent.

PCl5 PCl3

SOCl21

23

E ester

Na2CO3/NaHCO3 named carbonate

metal e.g.Mg

no reaction

no reaction

named indicator

no effect

No reaction1

F acid


Effervescence or CO2

metal e.g.Mg

Effervescence or H2

named indicator

acid colour

fumes1


(ii) Single reagent

If wrong single reagent, CE = zeroIncomplete single reagent (e.g. carbonate) or wrongformula (e.g.NaCO3) loses reagent mark, but mark onFor “no reaction” allow “nothing”

Different reagents

If different tests on E and F; both reagents and anyfollow on chemistry must be correct for first (reagent) mark.Reagent must react: i.e. not allow Tollens onG (ketone) – no reaction.Second and third marks are for correct observations.

1

i.e. for different tests on E and F, if one reagent is correctand one wrong, can score max 1 for correct observationwith correct reagent.

G ketone

AgNO3

no reaction


water

no reaction

named indicator

no effect

Named alcohol

no reaction

Named amine or ammonia

no reaction1


H Acyl chloride

AgNO3

(white) ppt


Effervescence or CO2 or fumes or exothermic

water

fumes

named indicator

acid colour

Named alcohol

Smell or fumes

Named amine or ammonia

fumes1

Allow iodoform test or Brady’s reagent (2,4,dnph) test (both positivefor G)

(iii) Single reagent

If wrong single reagent, CE = zeroIncomplete single reagent (e.g. carbonate) or wrongformula (e.g.NaCO3) loses reagent mark, but mark on

For “no reaction” allow “nothing”

Different reagents

If different tests on E and F; both reagents and any followon chemistry must be correct for first (reagent) mark.

Reagent must react: i.e. not allow Tollens onG (ketone) – no reaction.

Second and third marks are for correct observations.

i.e. for different tests on E and F, if one reagent is correctand one wrong, can score max 1 for correct observationwith correct reagent.

1


J Primary alcohol

K2Cr2O7/ H+

goes green

KMnO4/ H+

decolourised / goes brown

Lucas test (ZnCl2/HCl)

Penalise missing H+ but mark on1

K Tertiary alcohol

K2Cr2O7/ H+

No reaction

KMnO4/ H+

no reaction

Lucas test (ZnCl2/HCl)

Rapid cloudiness1

If uses subsequent tests e.g. Tollens/Fehlings, test must be onproduct of oxidation

(b) (i) 3,3-dimethylbutan-1-ol

Allow 3,3-dimethyl-1-butanol1

41

Triplet on three1

(ii) 2-methylpentan-2-ol

Allow 2-methyl-2-pentanol1

51

Singlet or one or no splitting1

[15]

(a) (i) Green

Ignore shades of green.1

24


(ii) Excess acidified potassium dichromate(VI)1

Reflux (for some time)1

In the diagram credit should be given for• a vertical condenser

Lose M3 and M4 for a distillation apparatus.1

• an apparatus which would clearly work

Do not allow this mark for a flask drawn on its own.

Penalise diagrams where the apparatus is sealed.1

(iii) Distillation1

Immediately (the reagents are mixed)1

(b) Keep away from naked flames

Allow heat with water-bath or heating mantle.

If a list is given ignore eye protection, otherwise lose this mark.1

(c) (i) Tollens’ or Fehling’s reagents

Incorrect reagent(s) loses both marks.

Accept mis-spellings if meaning is clear.1

Silver mirror / red ppt. formed

Accept ‘blue to red’ but not ‘red’ alone.1

(ii) Sodium carbonate (solution) / Group II metal

Allow indicator solutions with appropriate colours.

Accept any named carbonate or hydrogen carbonate.1

Effervescence / evolves a gas

Accept ‘fizzes’.1

(d) Propanoic acid

If this mark is lost allow one mark if there is reference to strongerintermolecular forces in the named compound.

Lose M1 and M3.1

Contains hydrogen bonding1


Some comparison with other compounds explaining that the intermolecular forces arestronger in propanoic acid

1

[15]

1-chloropropane no visible change

Accept ‘small amount of precipitate’ or ‘precipitate forms slowly’.1

25

ethanoyl chloride white precipitate

Accept ‘large amount of precipitate’ or ‘precipitate formsimmediately’.

1

[2]

(a) diethylamine OR ethyl ethanamine OR ethyl aminoethane

ignore N–1

26

(b) For (b) and (c)

There are three valid routes for this synthesis calledRoutes A, B and C below

• Decide which route fits the answer best (this may not be thebest for part b) to give the candidate the best possible overall mark.

• Mark part (b)

• For this best route mark the mechanism and reagent independently

• Migration from one route to another is not allowed

• Either name or formula is allowed in every case.

• Ignore conditions unless they are incorrect.

Route A Route B Route C

F CH3CH2Br or CH3CH2Cl C2H6 CH3CH2OH 1

G CH3CH2NH2 ethylamine ORethanamine OR aminoethane

CH3CH2Br ORCH3CH2Cl

CH3CH2Br ORCH3CH2Cl

1


(c)

Route A Route B Route C

Step1

Reagent(s) HBr OR HCl H2/Ni (NotNaBH4)

H2O & H3PO4

ORH2O & H2SO4

1

Mechanism Electrophilicaddition

addition (allowelectrophilic ORcatalytic but notnucleophilic)ignorehydrogenation

Electrophilicaddition

1

Step 2 Reagent(s) NH3 Cl2 OR Br2 HBr OR KBr &

H2SO4 ORPCl3 OR PCl5OR SOCl2

1

Mechanism Nucleophilicsubstitution

(free) radicalsubstitution

Nucleophilicsubstitution

1

Step 3 Reagent(s) CH3CH2Br

ORCH3CH2Cl

CH3CH2NH2 ORNH3 butpenalise excessammonia here

CH3CH2NH2

OR NH3 butpenaliseexcessammonia here

1

Mechanism Nucleophilicsubstitution



1

(d) tertiary amine OR triethylamine OR (CH3CH2)3NQuaternary ammonium saltOR tetraethylammonium bromide OR chloride OR ionOR (CH3CH2)4N+ (Br– OR Cl–)

1

further substitution will take place ORdiethylamine is a better nucleophile than ethylamine

1

[11]

(a) pH on the y-axis, volume of alkali on the x-axis

If axes unlabelled use data to decide that pH is on y-axis.1

27

Uses sensible scales

Lose this mark if plotted paths do not cover half of the paper.

Lose this mark if the graph plot goes off the squared paper.1

Labels the axes

Allow mark for axes labelled ‘pH’ and ‘volume’.1


Plots all of the points correctly1

Line through the points is smooth and has the correct profile

Ignore 0–5 cm3 section of the graph.

Lose this mark if graph is kinked or not a single line.1

Line ignores the point at 12 cm3

Lose this mark if point clearly not treated as an anomaly.1

(b) (i) 24.4 cm3 ± 0.2

If no answer in (i) allow answer written on the graph.

Allow this answer only.

Do not penalise precision.1

(ii) 12.2 cm3 ± 0.1

If no answer in (ii), allow answer written on the graph.

Allow answer to (i) divided by 2.


(iii) 3.9 ± 0.2

If no answer in (iii), allow answer written on the graph.

Consequential marking from (ii)

Lose this mark if answer not given to 1 dp.1

(c) pKa = – log Ka or Ka = 10x, where x = – (answer to b(iii))1

1.26 × 10–4

3.7 to 4.1 gives Ka = 7.9 × 10–5 to 2.0 × 10–4

Consequential marking from b(i).

Correct answer without working scores 1 mark only.


(d) Methanoic acid

Consequential marking from (c).

pKa = 3.7 gives methanoic acid.

pKa = 4.1 gives ethanoic acid.

No lucky guesses – candidates must apply answer from (c).

Do not allow answers based on data given in (f).1


(e) Error in using pipette is 0.2% andError in using burette is 0.15 × 100 / (answer to b(i))

Using 24.4 for burette gives 0.6%

Do not penalise precision.

Allow if errors are given without working.

Lose mark if the burette error is not calculated on b(i).

If the error being calculated is not stated, allow if the calculationsare in the same order as in the question (pipette, burette).

1

(f) Difference is 1.6 × 10–4 – 1.26 × 10–4 = 0.34 × 10–4

Allow consequential answer from (c).

Do not penalise precision.

0.34 × 100 / 1.6 is a 21% error

Correct final answer without working scores 1 mark.

Using 1.9 × 10–4 gives 0.3 × 10–4 and 18.8%.1

(g) Calibrate meter or thermostat the mixture or maintain constant temperature

Do not allow ‘repeat experiment’.1

(h) Mixture is a buffer1

[16]

(a) Log (1 / time) on the y-axis + log (vol) on x-axis

If axes unlabelled use data to decide that log (1 / time) is on the

y-axis1

28

Sensible scales

Lose this mark if the plotted points do not cover at least half of thepaper

Lose this mark if the graph plot goes off the squared paper

Lose this mark if plots a non-linear / broken scale

Lose this mark if uses an ascending y-axis of negative numbers1

Plots points correctly ± one square1

Line through the points is smooth

Lose this mark if the candidate’s line is doubled1


Line through the points is best fit – ignores last point

Must recognise that point at 25 cm3 is an anomaly

If wrong graph, mark consequentially on anomaly if correctlyplotted.

A kinked graph loses smooth and best fit marks1

(b) Uses appropriate x and y readings

Allow taken from table or taken or drawn on graph

Must show triangle on graph or such as 1

Correctly calculates gradient 0.95 ± 0.02

Ignore positive or negative sign

Correct answer only with no working scores this mark1

Answer given to 2 decimal places1

(c) First order or order is 1

Allow consequential answer from candidate’s results1

(d) Thermostat the mixture / constant temperature / use a water bathor Colorimeter / uv-visible spectrometer / light sensor to monitor colour change

1

Reaction / rate affected by temperature changeor Eliminates human error in timing / more accurate time of colour change

1

[11]

(Calibrate) meter with solution(s) of known pH/buffer(s)

Do not accept ‘repeat reading’1

29

Adjust meter/plot calibration curve1

[2]

(a) Mg + 2C6H4(OH)COOH → (C6H4(OH)COO)2Mg + H2

Accept multiples, including fractions.1

30

(b) Gas syringe / inverted burette over water / measuring cylinder over water

Collection apparatus must show graduations or be clearly labelled(eg syringe, burette, measuring cylinder).

1

[2]


(a) Burette131

Because it can deliver variable volumes1

(b) The change in pH is gradual / not rapid at the end point1

An indicator would change colour over a range of volumes of sodium hydroxide

Allow indicator would not change colour rapidly / with a few drops ofNaOH

1

(c) [H+] = 10–pH = 1.58 × 10–12

1

Kw = [H+] [OH–] therefore [OH–] = Kw / [H+]1

Therefore, [OH–] = 1 × 10–14 / 1.58 × 10–12 = 6.33 × 10–3 (mol dm–3)

Allow 6.31–6.33 × 10–3 (mol dm–3)1

(d) At this point, [NH3] = [H+]

Therefore Ka1

[H+] = 10–4.6 = 2.51 × 10–5

1

Ka = (2.51 × 10–5)2 / 2 = 3.15 × 10–10 (mol dm–3)

Allow 3.15 – 3.16 × 10–10 (mol dm–3)1

(e) When [NH3] = [NH4+], Ka = [H+] therefore – log Ka= – log [H+]

Answer using alternative value1

Therefore pH = –log10(3.15 × 10–10) = 9.50

M2 pH = – log10(4.75 × 10–9) = 8.32

Allow consequential marking based on answer from part (d)1

[12]


(a) Mg + H2O → MgO + H2

ignore state symbols1

White solid / powder / ash / smoke

ignore precipitate

ignore fumes1

(Bright) white light / flame

allow glow

penalise effervescence under list principle1

32

(b) 2Na + O2 → Na2O / 4Na + O2 → 2Na2O

Allow multiples, ignore state symbols

Allow 2Na + O2 → Na2O21

white / yellow solid / ash / smoke

ignore precipitate

ignore fumes1

orange / yellow flame1

[6]


this question is about nitrobenzenes

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