assessment unit a2 2 - frankly · pdf filesolution is added to cobalt(ii) sulphate ... acid...

TIME

1 hour 30 minutes.

INSTRUCTIONS TO CANDIDATES

Write your Centre Number and Candidate Number in the spaces

provided at the top of this page.

Answer all fifteen questions.

Answer all ten questions in Section A. Record your answers by

marking the appropriate letter on the answer sheet provided. Use only

the spaces numbered 1 to 10. Keep in sequence when answering.

Answer all five questions in Section B. Write your answers in the

spaces provided in this question paper.

INFORMATION FOR CANDIDATES

The total mark for this paper is 90.

Quality of written communication will be assessed in

question 13(a)(v).In Section A all questions carry equal marks, i.e. two marks for each

question.

In Section B the figures in brackets printed down the right-hand side

of pages indicate the marks awarded to each question or part question.

A Periodic Table of Elements (including some data) is provided.

A2C2S7 2930

ADVANCEDGeneral Certificate of Education

2007

Chemistry

Assessment Unit A2 2

assessing

Module 5: Analytical, Transition Metals and Further

Organic Chemistry

[A2C21]

WEDNESDAY 30 MAY, AFTERNOON

A2C

21

71

Centre Number

Candidate Number

For Examiner’s use only

Question Marks

Number

Section A

1–10

Section B

11

12

13

14

15

TotalMarks

A2C2S7 2930 2 [Turn over

Section A

For each of the questions only one of the lettered responses (A – D) is correct.

Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet.

1 Which one of the following formulae represents the complex formed when excess ammonia

solution is added to cobalt(II) sulphate solution?

A [Co(NH3)4(H

2O)

2]2+

B [Co(NH3)4]2+

C [Co(NH3)6]2+

D [Co(NH3)2(H

2O)

4]2+

2 Which one of the following organic compounds gives rise to the largest number of peaks in a

high resolution n.m.r. spectrum?

A CH3CH

2COCH

2CH

3

B CH3COOH

C CH3CH

2Br

D CH3CH

2COOCH

3

3 In which one of the following complexes does the transition metal present have an oxidation

state of +2?

A [Co(NH3)4Cl

2]Cl

B [Cu(CN)4]3–

C K3[Fe(CN)

6]

D [Ni(en)3]Cl

2

4 What is the total number of isomers of dichlorobenzene, C6H

4Cl

2?

A 2

B 3

C 4

D 5

A2C2S7 2930 2


5 The magnesium content of a sample of water may be determined by titration with edta using

a suitable indicator. Which one of the following statements is incorrect?

A One mole of edta reacts with one mole of magnesium ions.

B The solution must be buffered at a pH of approximately 10.

C The complex formed between edta and magnesium ions is coloured.

D The magnesium ions forms a stable complex with the indicator.

6 Sulphur dichloride dioxide, SO2Cl

2, reacts with water to form a mixture of only hydrochloric

acid and sulphuric acid. Calculate the hydrogen ion concentration of the solution formed

when 0.02 mole of SO2Cl

2 is dissolved to make 250 cm3 of solution.

A 0.08 mol dm–3

B 0.16 mol dm–3

C 0.24 mol dm–3

D 0.32 mol dm–3

7 In the reaction

which species attacks the benzene ring?

A HNO3

B NO2

C NO2

+

D H2NO

3+

NO2O2N

NO2

CH3

HNO3/H2SO4⎯⎯⎯⎯→

CH3


8 A mixture of two amino acids was subjected to “two-way” chromatography. After elution

with solvent 1 the paper was removed, dried and rotated through 90° and eluted with

solvent 2. The resultant chromatogram is shown below.

The Rf values for some amino acids are given.

amino acid Rf (solvent 1) Rf (solvent 2)

alanine 0.30 0.65

aspartic acid 0.14 0.37

glycine 0.29 0.42

lysine 0.21 0.52

valine 0.54 0.65

Which two amino acids does the mixture contain?

A alanine and aspartic acid

B alanine and valine

C glycine and lysine

D glycine and valine

solvent front 1

solv

ent fro

nt 2

originalspot


9 50 cm3 of a gaseous hydrocarbon requires exactly 250 cm3 of oxygen for complete

combustion and produces 150 cm3 of carbon dioxide. What is the formula of the

hydrocarbon?

A C3H

4

B C3H

8

C C5H

10

D C5H

12

10 Each of the copper compounds below can be reduced to the metal. Which one of the

compounds would produce the greatest mass of copper metal if 5.0 g of each compound were

reduced?

A CuO

B Cu2O

C CuS

D CuF2


Examiner Only

Marks Remark

Section B

Answer all five questions in the spaces provided.

11 Instrumental analysis is commonly used to deduce the identity and structure

of unknown organic compounds. An organic compound of molecular

formula C5H

10O was subjected to a series of tests.

(a) The compound produced the following mass spectrum:

Suggest the formulae of two ions which would give rise to the peak at

m/e 43.

__________________________________________________________

_______________________________________________________ [2]

43100

%abundance

m/e


Examiner Only

Marks Remark

(b) The infra-red spectrum for the compound is shown below:

Identify the functional group which has the largest absorbance.

_______________________________________________________ [1]

(c) Use your answers to parts (a) and (b) to deduce the structural formula

of the compound.

_______________________________________________________ [1]

4000 3000 2000 1500 1000

0

100

Absorbance

C

Bond Absorption Bond Wavenumber/cm–1

C––H 2850–3300

C––O 1000–1300

O––H 2500–3500

C––O 1680–1750


Examiner Only

Marks Remark

12 Para red is a dye which was detected in cayenne pepper sourced from

Uzbekistan. The discovery of this banned dye in foodstuffs led to

withdrawal of many products from supermarket shelves. The dye can be

prepared as follows:

(a) (i) Name the reagents used in step A.

______________________________________________________

____________________________________________________ [2]

(ii) Explain why a low temperature must be used in step A.

______________________________________________________

____________________________________________________ [1]

(b) (i) Deduce a possible structure for Para red.

[2]

(ii) Explain why Para red is coloured.

______________________________________________________

____________________________________________________ [2]

NO2

N2 Cl–

A⎯→

NH2

NO2

⎯⎯⎯⎯→

OH

Para red

+


BLANK PAGE

(Questions continue overleaf)


Examiner Only

Marks Remark

13 Transition metal chemistry is characterised by redox reactions, colour

changes and catalytic activity.

(a) The most common oxidation states in iron compounds are +2 and +3.

Iron(II) ions are readily oxidised to iron(III).

(i) Define the term oxidation in terms of electron transfer.

____________________________________________________ [1]

(ii) Iron(II) ions may be oxidised by bubbling chlorine gas through an

aqueous solution of the ions. State the colour change observed and

write an equation for the reaction.

______________________________________________________

____________________________________________________ [3]

(iii) State the electron structure of an iron(II) ion and an iron(III) ion

using spd notation.

iron(II) __________________________

iron(III) __________________________ [2]

(iv) Use the above electron structures to explain the relative stabilities

of the two ions.

______________________________________________________

____________________________________________________ [1]


Examiner Only

Marks Remark

(v) Describe how the percentage of iron in aluminium foil may be

determined using colorimetry. Your account should include how

you would:

● dissolve the foil

● oxidise the iron to the +3 oxidation state

● use a named reagent to produce a strongly coloured complex

● use a calibration curve to determine the concentration of iron in

solution

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

____________________________________________________ [4]

Quality of written communication [2]


Examiner Only

Marks Remark

(b) Trinitrotriammine cobalt(III), [Co(NO2)3(NH

3)3], is a yellow crystalline

substance which may be prepared by the following method.

Dissolve 12.2 g of cobalt(II) ethanoate tetrahydrate in 100 cm3 of hot water. Cool the solution in an ice-bath and add 10.4 g of sodium nitrite dissolved in 50 cm3 of “0.88” ammonia. Cool to 10 °C and carefully add 14 cm3 of 20 volume hydrogen peroxide solution followed by 2 g of activated charcoal. After stirring, the mixture is left for 10 minutes before boiling for 30 minutes. Filter the hot solution to remove the activated charcoal and cool the filtrate in an ice-bath. Filter off the crystals, wash with cold ethanol and dry.

(i) Deduce the formula of cobalt(II) ethanoate tetrahydrate.

____________________________________________________ [2]

(ii) State and explain the role of hydrogen peroxide in this preparation.

______________________________________________________

____________________________________________________ [2]

(iii) Suggest the shape of the trinitrotriammine cobalt(III) complex.

____________________________________________________ [1]

(iv) Deduce the coordination number of cobalt in the trinitrotriammine

cobalt(III) complex.

____________________________________________________ [1]

(v) 20 volume hydrogen peroxide is so named because one volume of

the solution produces 20 times this volume of gaseous oxygen on

complete decomposition at 20 °C and one atmosphere pressure i.e.

1 cm3 of solution will produce 20 cm3 of oxygen gas.

2H2O

2(aq) → 2H

2O(l) + O

2(g)

Calculate the concentration of 20 volume hydrogen peroxide in

mol dm–3.

______________________________________________________

______________________________________________________

____________________________________________________ [3]


Examiner Only

Marks Remark

(c) Aqueous cobalt(II) ions catalyse the decomposition of chlorate(I) ions,

ClO–, to form oxygen gas.

(i) Use three equations to show the three steps involved in this

catalytic decomposition.

______________________________________________________

______________________________________________________

____________________________________________________ [3]

(ii) Explain whether this catalysis is homogeneous or heterogeneous.

______________________________________________________

____________________________________________________ [1]


Examiner Only

Marks Remark

14 Cyanides are salts of hydrocyanic acid (hydrogen cyanide). Organic

cyanides have the formula RCN and are called nitriles.

(a) Potassium cyanide is used to extract gold from its ore according to the

following reaction:

4Au(s) + 8CN–(aq) + 2H2O(l) + O

2(g) → 4[Au(CN

2)]–(aq) + 4OH–(aq)

(i) Name the type of bond formed between the gold ions and the

cyanide ions.

____________________________________________________ [1]

(ii) This process was simulated in the laboratory. Calculate the volume

of 2 M potassium cyanide solution needed to extract 1 kg of gold

from its ore.

______________________________________________________

______________________________________________________

____________________________________________________ [3]

(b) Cyanogen, C2N

2, is a colourless gas with the characteristic smell of

bitter almonds.

(i) Draw a dot and cross diagram to show the bonding in cyanogen.

[2]

(ii) State and explain the shape of the cyanogen molecule.

______________________________________________________

______________________________________________________

____________________________________________________ [2]

(iii) Cyanogen may be prepared by warming potassium cyanide

solution with copper(II) sulphate to form copper(II) cyanide.

Decomposition of copper(II) cyanide yields copper(I) cyanide and

cyanogen.

Write the equation for the decomposition of copper(II) cyanide.

____________________________________________________ [2]


Examiner Only

Marks Remark (c) Ethanenitrile may be prepared by boiling an alcoholic solution of

potassium cyanide with iodomethane.

(i) Write the equation for the formation of ethanenitrile.

____________________________________________________ [1]

(ii) Assuming this occurs as a single step nucleophilic substitution

reaction, suggest the structure of the transition state formed.

[1]

(iii) Name the reagents required to bring about the following changes.

A __________________________

B __________________________

C __________________________ [3]

CH3CH2NH2

A←⎯ CH3CN

←⎯

⎯

←⎯

⎯

CH3COOH

CH3COONa

B

C


Examiner Only

Marks Remark

(d) Potassium thiocyanate is prepared by boiling potassium cyanide

solution with sulphur. It is extremely soluble in water and reacts readily

with silver nitrate solution to form a precipitate of silver thiocyanate.

This reaction may be used, as follows, to determine the chloride content

in cheese.

Weigh out accurately approximately 1.5 g of cheese into a conical flask. Add 10 cm3 of water, 25.0 cm3 of 0.05 M silver nitrate solution (an excess) and 10 cm3 of concentrated nitric acid. Boil for 10 minutes. Cool and add a further 50 cm3 of water. The excess silver nitrate is determined by titration with standard potassium thiocyanate solution using an iron(III) indicator. At the end-point the aqueous iron(III) ions react with excess thiocyanate ions.

(i) Explain the term standard solution.

____________________________________________________ [1]

(ii) State the colour observed at the end-point.

____________________________________________________ [1]

(iii) State the formula of the iron(III) complex formed at the end-point.

____________________________________________________ [1]

(iv) Write the equation for the reaction between aqueous solutions

of silver nitrate and potassium thiocyanate to form the silver

thiocyanate precipitate.

____________________________________________________ [1]


Examiner Only

Marks Remark

(v) In an experiment 1.48 g of cheese was analysed as above. The

excess silver nitrate required 14.3 cm3 of 0.05 M potassium

thiocyanate solution for complete reaction. Calculate the chloride

content, in grams, per gram of cheese.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

____________________________________________________ [4]


Examiner Only

Marks Remark

15 Patients suffering from Parkinson’s disease have a deficiency of the brain

neurones that produce the neurotransmitter dopamine.

(a) Explain why dopamine should be very soluble in water.

__________________________________________________________

_______________________________________________________ [2]

(b) Dopamine is a base which behaves as a primary amine.

(i) Compare and suggest an explanation for the relative basic strengths

of dopamine, ammonia and phenylamine.

______________________________________________________

______________________________________________________

______________________________________________________

____________________________________________________ [3]

(ii) Write an equation for the reaction of dopamine with hydrochloric

acid.

____________________________________________________ [1]

CH2HO

dopamineHO

CH2

NH2

(c) Treatment of Parkinson’s disease often involves the use of L-dopa

which is the natural precursor of dopamine.

L-dopa

(i) Deduce the molecular formula of L-dopa.

____________________________________________________ [1]

(ii) Explain why L-dopa is optically active.

______________________________________________________

____________________________________________________ [2]

(iii) Draw the structure of the dipolar ion (zwitterion) formed when

L-dopa is dissolved in water.

[1]

CH2HO

HO

CH

COOH

NH2

THIS IS THE END OF THE QUESTION PAPER

A2C2S7 2930 19

Examiner Only

Marks Remark

S – 1/07 – 7-164-1 [Turn over

assessment unit a2 2 - frankly · pdf filesolution is added to cobalt(ii) sulphate ... acid...

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