Heep Woh Collegeaerodrive.ccchwc.edu.hk/~lck/ckraylau/alchem/1011ALmock2.pdf · 2011-01-26 · Paper II / 5 2010 - 2011 / Form Seven / AL Chemistry / Mock Examination / Paper II

Paper II / 1

2010 - 2011 / Form Seven / AL Chemistry / Mock Examination / Paper II / C.K.Lau

CCC HEEP WOH COLLEGE 2010 – 2011 MOCK EXAMINATION

F.7 AL CHEMISTRY PAPER II 1:30pm – 4:30pm (3 hours)

20-1-2011 Question-Answer Book

SETTER: MR. LAU C.K.

Name: _______________________ Class: Form 7S Class Number: _______

Total Mark: ________________ 1. This paper must be answered in English.

2. There are TWO sections in this paper, Section A and Section B.

3. Section A carries 60 marks and Section B carries 40 marks.

4. All questions in Sections A and B are COMPULSORY. Answers are to be written in this Question-Answer Book.

If you use supplementary answer sheet(s) for these two sections, write your Name and Class Number on

each sheet and fasten them with string to this Question-Answer Book.

5. Some useful constants and a Periodic Table are printed below:

Periodic Table

Useful Constants

Gas constant, R = 8.31 J K-1 mol-1 Speed of light in vacuum, c = 3.00 x 108 m s-1

Faraday constant, F = 9.65 x 104 C mol-1 Ionic product of water at 298K, Kw = 1.00 x 10-14 mol2 dm-6

Avogadro constant, L = 6.02 x 1023 mol-1 Specific heat capacity of water = 4.18 J g-1 K-1

Planck constant, h = 6.63 x 10-34 J s Molar Volume of gas at r.t.p. = 24.0 dm3 mol-1

Characteristic Infra-red Absorption Wavenumber Ranges (Stretching modes)

Bond Compound type Wavenumber range / cm-1

C=C Alkenes 1610 to 1680

C=O Aldehydes, ketones, carboxylic acids, esters 1680 to 1750

CC Alkynes 2070 to 2250

CN Nitriles 2200 to 2280

OH Acids (hydrogen-bonded) 2500 to 3300

CH Alkanes, alkenes, arenes 2840 to 3095

OH Alcohols, phenols (hydrogen-bonded) 3230 to 3670

NH Amine 3350 to 3500

/ 100

Paper II / 2


Section A: Answer ALL questions in this Section. Write your answers in the spaces provided.

Question 1 [20 marks]

(a) 40.0 cm3 of ethanoic acid, CH3COOH(aq), was titrated with potassium hydroxide solution,

KOH(aq) at 298K. The initial pH, before the addition of KOH(aq) was 2.70. At the equivalence

point of titration, the pH was 8.90.

(i) Explain the difference between the equivalence point and the end point of a titration.

(ii) Given the dissociation constant of ethanoic acid at 298 K is 1.80×10–5 mol dm–3, calculate

(I) the initial concentration of ethanoic acid;

(II) the volume of the KOH(aq) added to the equivalence point;

(III) the concentration of the KOH(aq).

(7 marks)

Paper II / 3


(b) Explain the following:

(i) The dipole moment of PCl3 is 0.93D, whereas PCl5 has no net dipole moment.

(ii) Sodium dichromate(VI) is more soluble in water than potassium dichromate(VI).

(4 marks)

(c) Aluminium(III) chloride forms an addition compound with triethylamine.

(i) What is the likely composition of this addition compound? Draw a sketch to show its

shape.

(ii) What is the nature of bonding involved in this addition compound?

(3 marks)

Paper II / 4


(d) (i) Using the concept of activation energy, together with an appropriate sketch of the

Maxwell-Boltzmann distribution, explain why the addition of a suitable catalyst speeds up a

chemical reaction.

(ii) The decomposition of solutions of hydrogen peroxide is catalysed by certain transition

element ions.

2H2O2(aq) 2H2O(l) + O2(g)

Suggest a mechanism for the catalysis of this reaction by Fe2+ ions.

(You should refer to the standard electrode potentials given below)

O2(g) + 2H+(aq) + 2e– H2O2(aq) +0.68V

Fe3+(aq) + e– Fe2+(aq) +0.77V

H2O2(aq) + 2H+(aq) + 2e– 2H2O(l) +1.77V

O2(g) + 4H+(aq) + 4e– 2H2O(l) +1.23V

Fe2+(aq) + 2e– Fe(s) –0.44V

2H+(aq) + 2e– H2(g) 0.00V

(6 marks)

Paper II / 5



(a) The electrolysis of a solution of potassium fluoride in a mixed solvent of hydrogen fluoride and

water produces a colourless triatomic gas A at the anode. When 0.900 g of A is introduced into

an evacuated vessel of 1.00 dm3 capacity at a temperature of 282 K, it produces a pressure of

3.91×104 Pa.

(i) Calculate the relative molecular mass of A.

(ii) Suggest the molecular formula and the shape of A.

(3 marks)

(b) In acidic solution, bromide ion react with bromate(V) ion to form bromine and water. The

process of the reaction can be followed by adding a fixed amount of phenol together with

some methyl red indicator. The bromine produced during the reaction reacts very rapidly with

phenol. When all the phenol is consumed, any further bromine produced bleaches the

indicators immediately. So the time for the reaction to proceed to a given point may be

determined.

Experimental data:

Experiment Temperature/ °C Time for the disappearance of the red colour/ s

1 30 1054

2 37 595

3 41 387

4 44 306

5 49 211

(i) Write a balance ionic equation for the reaction between bromide ion and bromate(V) ion

in acidic medium.

(ii) Give an equation for the reaction between phenol and bromine.

Paper II / 6


(iii) Based on the Arrhenius equation, derive another equation so that time for the complete

disappearance of the red colour(abbreviated as “t”) can be related to Ea.

(iv) Hence, or otherwise, determine Ea by plotting a suitable graph.

Paper II / 7


(v) Explain briefly the following in molecular terms:

(I) temperature rise can increase reaction rate.

(II) a reaction with low activation energy proceeds faster.

(9 marks)

(c) Hydrangeas are flowering plants which commonly have pink flowers. They produce blue flowers

only in soils which contain high concentrations of Mg2+(aq). The pH of well-limed soil is 9.00,

whereas the pH of peat-based soil is 6.50. The numerical value of the solubility product, Ksp of

magnesium hydroxide is 1.80 ×10–12 mol3 dm–9.

(i) By calculating the theoretical maximum value of [Mg2+(aq)] in the two types of soil,

deduce which type of soil favours good cultivation of blue hydrangeas.

(ii) Horticulturalists use ammonium magnesium sulphate, (NH4)2Mg(SO4)2‧6H2O, to provide

Mg2+ as well as nitrogen. Explain why NH4+(aq) helps the uptake of Mg2+ by the plant.

(5 marks)

Paper II / 8


(d) The figure below can be used to represent the unit cell of either zinc blende (ZnS) or diamond:

Making use of this figure, describe the similarities and differences of the crystal lattice present in

zinc blende and diamond.

(3 marks)

Paper II / 9



(a) (i) State what is meant by “standard electrode potential of a metal”.

(ii) The quantitative relationship showing reduction potential (E) of Mn+(aq)|M(s) under

non-standard condition is given by Nernst equation at 298 K:

E = E + n

0.059log [Mn+(aq)]

where n is the number of electrons transferred in the half-equation.

Calculate the electrode potential of a zinc rod dipping into a solution containing 0.0100

mol dm-3 Zn2+ at 298K.

(iii) A cell is set up as below:

(I) Prove that the e.m.f. of this cell at non-standard condition is

e.m.f = 1.56 – 2

0.059log

2

2

)]aq(Ag[

)]aq(Zn[

Paper II / 10


(II) When this cell is discharged and reach equilibrium, what is the value of the e.m.f. of

this cell at equilibrium?

(III) Calculate the equilibrium constant, Kc, of the following reaction at 298 K.

2Ag+(aq) + Zn(s) Zn2+(aq) + 2Ag(s)

Given: Zn2+(aq) + 2e– Zn(s) –0.76

Ag+(aq) + e– Ag(s) +0.80

(6 marks)

(b) For the reaction

H2(g) + C2H4(g) C2H6(g)

calculate the enthalpy of the above reaction by two different methods using

(I) the enthalpy of formation at 298K

Hof of C2H4 = +52.3 kJ mol1 ; Hof of C2H6 = 84.6 kJ mol1 ; and

Paper II / 11


(II) the average bond energies at 298K

HH +436 kJ mol1;

CH +414 kJ mol1;

C=C +620 kJ mol1;

and CC +347 kJ mol1.

Comment on the difference between the enthalpy of reaction obtained by the two methods.

(7 marks)

(c) A series of experiments was carried out on B, an ionic salt, to determine its identity.

1 Some solid B was tested with flame test and it gives lilac flame.

2 Some solid B was dissolved in distilled water. Aqueous silver nitrate(V) acidified with dilute

nitric(V) acid was added and a cream precipitate was formed, which only slightly

dissolved in dilute aqueous ammonia but was soluble in concentrated ammonia solution.

3 Some solid B was heated with concentrated sulphuric(VI) acid. The mixture of fumes

produced was passed into water and the solution labelled C. The solution C was strongly

acidic and coloured pale brown.

4 A sample of solution C was mixed with an excess of an aqueous solution of potassium

iodide, then the colour of the solution turned to a very dark brown. The solution turned dark

blue on adding one drop of starch solution but adding an excess of sodium thiosulphate

solution removed the colour completely.

(i) Identify B.

(ii) Identify the component of the fumes which was responsible for the solution C being

strongly acidic.

Paper II / 12


(iii) Account for the production of the pale brown colour in solution C.

(iv) The starch solution turned dark blue. What was indicated by this change?

(v) Write an ionic equation for the reaction which led to the disappearance of the dark blue

colour on adding excess sodium thiosulphate solution.

(5 marks)

(d) Draw a labelled diagram to show the overlapping of orbitals of ethene.

(2 marks)

End of Section A

Paper II / 13


Section B: Answer ALL the questions on the Answer Book provided.


(a) Identify A, B, C, D and E. A is the reagent and condition needed to bring about the reaction. B,

C, D and E are the major organic products of the reactions.

(i)

A

Br

A:

(ii)

BKMnO4, H2SO4(aq)

heat

B:

(iii)

C

NH

N

O2N

CH3O

reflux

NaOH(aq)

C:

(iv)

COH

CH3

CH3

OH polymer DCOCl2

D:

(v)

EC CCH2CH

CH3

N

CH2CH3

O

CH3

CH3excess CH3I

E:

(5 marks)

Paper II / 14


(b) An organic iodide F is hydrolysed in dilute NaOH(aq) to give alcohol G at 298K.

CH3CH2O

CH3

I

CH3

F

CH3CH2O

CH3

OH

CH3

G

(i) Outline a mechanism of the reaction.

(ii) Draw a labelled energy profile of the reaction.

(iii) Compared with iodide F, what change in rate would you expect when iodide H below is

hydrolysed under the same condition? Explain your answer and draw a suitable resonance

structure to illustrate the answer.

CH3CH2O

CH3

I

CH3

H

(7 marks)

Paper II / 15


(c) The structure of the active ingredient in aspirin tablets is COOH

O

O

CH3

As well as the active ingredient, aspirin tablets contain other substances. The aspirin content

was determined by the method indicated below:

Three aspirin tablets were crushed and then added to 25.0 cm3 of 1.00 M sodium hydroxide

solution and simmered for 30 minutes. When cooled the reaction mixture was diluted to 250.0

cm3 in a volumetric flask.

25.0 cm3 sample solution were then back titrated with 0.0500 M sulphuric acid until concordant

results were obtained. The average titre was 15.30 cm3.

(i) Write an equation for the alkaline hydrolysis of aspirin.

(ii) Calculate

(I) the number of moles of excess sodium hydroxide in the volumetric flask.

(II) the number of moles of sodium hydroxide which reacted with the aspirin.

(III) the average mass of pure aspirin in each tablet.

(iii) Why does the back titration technique have to be used to determine the mass of aspirin?

Paper II / 16


(iv) A sample of aspirin was prepared and then purified by crystallization. List the experimental

procedure involved.

(v) Describe a simple method to test whether the product you obtain from (iv) is pure and is

the desired product.

(8 marks)

Paper II / 17



(a) Salbutamol is used for the relief of bronchospasm in conditions such as asthma. Its structure is

given: H

OH

OH

N

CH3

CH3

CH3

OH

The clinical uses of Salbutamol are specifically indicated for the following conditions: acute

asthma and symptom relief during maintenance therapy of asthma and it has a protection

against exercise-induced asthma. However, the adverse effects of Salbutamol include tremor,

palpitations and headache.

Infrequent adverse effects include tachycardia, muscle cramps, agitation, and hyperactivity in

children.

(i) Draw the major structure of Salbutamol when it exists at

(I) 1M HCl;

(II) 1M NaOH.

(ii) The above structure can represent two stereoisomers. Draw the three-dimensional

structures of the two stereoisomers and state a physical property which is different for the

two stereoisomers.

(iii) Would you expect both stereoisomers have the same medical effect? Explain briefly.

(5 marks)

Paper II / 18


(b) Methylbenzene is a useful starting material for the synthesis of many intermediates used to make

pharmaceuticals, dyes and agrochemicals.

(i) Suggest the reagents and conditions needed for each of the reactions I, III and IV in the

following scheme.

methylbenzene

CH3

CH2Cl

D

I

III

II

CH3

Cl

E

CO2H COCl

IVF

I: III:

IV:

(ii) Suggest the mechanism of the conversion of methylbenzene to E.

(iii) Describe and explain the relative ease of hydrolysis of the chloro compounds D, E and F.

(9 marks)

Paper II / 19


(c) An organic compound G, contains carbon, hydrogen and oxygen, with relative molecular mass

below 80. Upon complete combustion, 3.00 g of G gives 7.33 g of carbon dioxide and 3.00 g of

water.

(i) Deduce the molecular formula of G.

(ii) A portion of the infra-red spectrum of G is shown below:

What functional group(s) does compound G have? Explain your answer.

(iii) Draw all possible structures for G.

(iv) When G is treated with acidified potassium dichromate(VI) solution, no change can be

observed. Suggest a structure for G and explain your suggestion.

(6 marks)

End of Paper

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Heep Woh Collegeaerodrive.ccchwc.edu.hk/~lck/ckraylau/alchem/1011ALmock2.pdf · 2011-01-26 · Paper II / 5 2010 - 2011 / Form Seven / AL Chemistry / Mock Examination / Paper II