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Paper Reference(s)

6254/01

Edexcel GCEChemistry (Nuffield)

Advanced

Unit Test 4

Thursday 12 June 2008 Afternoon

Time: 1 hour 30 minutes

Materials required for examination Items included with question papers

Nil Nil

A calculator may be used.

Instructions to Candidates

In the boxes above, write your centre number, candidate number, your surname, initial(s) and yoursignature.AnswerALL the questions. Write your answers in the spaces provided in this question paper.Final answers to calculations should be given to an appropriate number of significant figures.

Information for Candidates

A Periodic Table is printed on the back cover of this question paper.The marks for the various parts of questions are shown in round brackets: e.g. (2).The total mark for this paper is 60. There are 16 pages in this paper. All blank pages are indicated.

Advice to Candidates

You are advised to show all steps in any calculations.You will be assessed on your ability to organise and present information, ideas, descriptions andarguments clearly and logically, taking into account your use of grammar, punctuation and spelling.

Examiners use only

Team Leaders use only

Question LeaveNumber Blank

1

2

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5

Total

Surname Initial(s)

Signature

Centre

No.

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Candidate

No.

Paper Reference

6 2 5 4 0 1

This publication may be reproduced only in accordance with

Edexcel Limited copyright policy.

2008 Edexcel Limited.

Printers Log. No.

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Answer ALL the questions. Write your answers in the spaces provided.

1. This question is about the reaction of iodine with propanone.

CH3COCH3(aq) + I2(aq) CH3COCH2I(aq) + H+(aq) + I(aq)

(a) Suggest, in outline, THREE different methods for following the rate of this reaction.

State which of the reactants or products could be measured by each method you

choose.

Method 1

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

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

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

Method 2

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

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

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

Method 3

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

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

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

(3)

(b) The reaction is extremely slow at room temperature in the absence of H+ ions as a

catalyst.

Suggest how you would quench the reaction before carrying out a titration method to

determine the concentration of iodine at different times.

Justify your answer.

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

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

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

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

(2)

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(c) A series of experiments was carried out, varying the concentrations of the reactants

and the catalyst. The following results were obtained.

Experiment[CH3COCH3]

/mol dm3[I2]

/mol dm3[H+]

/mol dm3Initial rate

/mol dm3 s1

1 1.00 0.010 0.10 2.8 106

2 1.00 0.010 0.20 5.6 106

3 1.50 0.010 0.20 8.4 106

4 1.50 0.020 0.10 4.2 106

The reaction is first order with respect to hydrogen ions, H+.

(i) Deduce the order of the reaction with respect to propanone, CH3COCH3. Justify

your answer.

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

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

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

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

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

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

(3)

(ii) Deduce the order of the reaction with respect to iodine, I2.

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

(1)

(iii) Hence give the rate equation for this reaction.

(1)

(iv) Which species are involved in the rate-determining step?

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

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

(1)

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(v) Suggest an equation for the reaction between the species in the rate-determining

step.

Explain why this step is likely to take place.

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

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

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

(2) Q1

(Total 13 marks)

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2. One of the alarm pheromones for ants, compound Q, has the molecular formula C6H10O.

(a) State what can be deduced about compound Q from each of the following pieces of

information.

(i) Q,C6H10O, is a non-cyclic organic compound. When saturated it would contain

14 hydrogen atoms.

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

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

(1)

(ii) Compound Q does not react with sodium.

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

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

(1)

(iii) One mole of compound Q reacts with one mole of bromine molecules, Br2, in the

absence of sunlight.

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

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

(1)

(iv) Compound Q gives a yellow precipitate with Bradys reagent,

2,4-dinitrophenylhydrazine.

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

(1)

(v) When compound Q is warmed with Benedicts solution, a red precipitate is

formed.

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

(1)

(vi) Compound Q exists in the trans form.

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

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

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

(1)

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(vii) Given that compound Q is a straight chain molecule with the two functional

groups next to one another, give the displayed formula ofQ.

(2)

(b) (i) Compound Q, C6H10O, can be converted into C6H14O in two steps.

Give the reagent and any catalyst needed for each step.

Step 1 .....................................................................................................................

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

Step 2 .....................................................................................................................

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

(2)

(ii) Name the functional group which would now be present?

................................................................................................................................(1) Q2

(Total 11 marks)

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3. Phosphorus(V) chloride dissociates as follows:

PCl5(s) PCl3(l) + Cl2(g) H= + 123.8 kJ mol1

Substance Standard entropy, S

/ J mol1 K1

PCl5(s) + 166.5

PCl3(l) + 217.1

Cl2(g) + 165.0

(a) (i) Explain why the entropy of solid phosphorus(V) chloride, PCl5, is smaller than

the entropy of liquid phosphorus(III) chloride, PCl3?

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

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

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

(1)

(ii) Calculate S

system for the forward reaction. Include a sign in your answer.

(1)

(iii) Is the sign ofS

system as you would expect? Fully justify your answer.

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

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

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

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

(2)

(b) Calculate S

surroundings for the forward reaction at 298 K. Include a sign and units in

your answer.

(2)

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(c) (i) Use your answers to calculate S

total for the forward reaction at 298 K. Include

a sign in your answer.

(1)

(ii) Comment on the position of equilibrium at 298 K.

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

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

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

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

(1)

(d) In an experiment to investigate this equilibrium, 41.7 g of phosphorus(V) chloride

(molar mass 208.5 g mol1) was heated in a closed vessel at 150 C until equilibrium

was established. The final pressure was found to be 4.32 atm and 0.15 moles

of phosphorus(V) chloride remained. At this temperature all of the reactants and

products are gaseous.

(i) Give the expression for the equilibrium constant, Kp, and its units at this

temperature.

(2)

(ii) Complete the table

Substance Moles at start Moles at equilibrium Partial pressure at

equilibrium,peq/atm

PCl5(g) 0.15

PCl3(g) 0

Cl2(g) 0

Total number of moles at equilibrium

(3)

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(iii) CalculateKp.

(1)

(iv) How would you expect the value ofKp to change, if at all, if the following

changes were made? Justify each of your answers.

A Only 20.85 g of phosphorus(V) chloride had been used.

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

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

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

B The temperature had been increased to 250 C.

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................................................................................................................................(2) Q3

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4. An important industrial compound, S, has the formula

C12H25 SO3Na+

(a) (i) Name the reagents and give the conditions where necessary for the two steps

needed to make

SO3Na+ from benzene.

Step 1 Reagent ......................................................................................................

Conditions .................................................................................................

Step 2 Reagent ......................................................................................................

(3)

(ii) Name the type of reaction in each step.

Step 1 .....................................................................................................................

Step 2 .....................................................................................................................

(2)

(b) (i) What is the specific name given to the reaction when an alkyl group is introduced

into the benzene ring by electrophilic substitution?

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

(1)

(ii) Give the molecular formula of the reagent and of the catalyst needed to make

C12H25 from benzene.

Reagent ..................................................................................................................

Catalyst ..................................................................................................................

(2)

(c) Suggest an important use for compound S.

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

(1) Q4

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5. Human blood plasma is a buffer solution. It partly owes its buffer properties to carbon

dioxide, produced by respiration, dissolving in the blood for transportation to the lungs.

Carbon dioxide dissolves in water establishing the equilibrium

CO2(aq) + H2O(l) H+(aq) + HCO3

(aq)

(a) (i) Write the expression forKa for this equilibrium and give its units.

Units ........................

(2)

(ii) What is the relationship between pKa andKa?

(1)

(b) Explain what is meant by a buffer solution.

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

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

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

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

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

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

(2)

(c) HCO3(aq) can act as an acid or a base.

CO2(aq) + H2O(l) H+(aq) + HCO3

(aq)

In this equilibrium, decide whether HCO3

(aq) is acting as an acid or as a base. Givethe reason for your decision.

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

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

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

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

(1)

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(d) A sprinter had the pH and total carbonate concentration, [CO2 + HCO3], of his blood

plasma measured immediately before and after a race. The following results wereobtained.

pHTotal carbonate concentration, [CO2 + HCO3

]

/ mol dm3

Before race 7.4 2.52 102

After race 7.3 1.98 102

The pH of a buffer solution is given by the equation

pH p [acid][base]

a= K log

For this equilibrium pKa is 6.5.

(i) Use this information, together with the data in the table, to calculate[acid]

[base]

before the race.

(2)

(ii) The concentration of HCO3 is 0.0224 mol dm3. Calculate the concentration of

CO2 before the race.

(1)

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(iii) Use your results from (d)(i) and (ii) to complete the table below which will allow

you to compare the results before and after the race.

[acid]

[base]

[HCO3]

/ mol dm3[CO2]

/ mol dm3

Before race 0.0224

After race 0.158 0.0171 0.00270

Two hypotheses have been proposed to explain why vigorous exercise results in

an increase in blood plasma acidity (from 7.4 to 7.3).

Greater muscle activity during a race requires:

either

Hypothesis I the combustion of larger quantities of glucose, resulting in an

increase in dissolved carbon dioxide and hence an increase in

acidity.

or

Hypothesis II partial oxidation of glucose to lactic acid and hence an increase

in acidity.

State, giving your reasons, which hypothesis is favoured by the data and your

calculations.

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

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

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

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

(2)

TOTAL FOR PAPER: 60 MARKS

END

Q5

(Total 11 marks)

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