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HKALE
Chemistry (AL)
1995 Paper I
1995
SECTION A
Answer ALL questions in this Section.
1.
(a)
Write your answers in the spaces provided.
(i) The first four successive ionization energies of an element A are 578, 1817, 2746 and 10813 kJ mo1 -1 respectively.
To which group in the Periodic Table does A belong?
(ii) The relative atomic mass of bromine is 79.90. It has two isotopes with mass numbers 79 and 81.
Calculate the relative abundance of each isotope.
(3 marks)
(b)
(i) What can you deduce from the fact that the spectral lines in the atomic emission spectrum of hydrogen are not
equally spaced?
(ii) In the atomic emission spectrum of hydrogen, the convergence limit for the Lyman series occurs at 3.275 X 10 15 Hz.
Calculate the ionization energy of hydrogen, in kJ mo1-1.
(3 marks)
(c)
Account for the fact that the carbon-oxygen bond lengths in CO, CO2 and CO32- are 0.113, 0.116 and 0.129
respectively.
(3 marks)
(d)
The iodination of propanone is catalysed by hydrogen ions.
The overall equation is:
CH3COCH3(aq)+I2(aq)  CH3COCH2I(aq)+HI(aq)
Using four mixtures B, C, D and E, the progress of the reaction was followed by colorimetric measurement.
The results are tabulated below.
Mixture
B
C
D
E
propanone
10.0
10.0
5.0
10.0
Composition by volume of mixture / cm3
water
1.00 M HCI
60.0
10.0
50.0
10.0
65.0
10.0
65.0
5.0
0.05 M I2 in KI
20.0
30.0
20.0
20.0
Initial rate
/mol dm-3 s-1
4.96 X 10-6
5.04 X 10-6
2.45 X 10-6
2.47 X 10-6
(i) Determine the effects of the changes in concentration of each of the reactants (iodine and propanone) and the
Catalyst (hydrochloric acid) on the reaction rate. Write the rate expression for the reaction.
(ii) For mixture B, calculate the rate constant for the reaction at the temperature of the experiment.
(Density of CH3COCH3 = 0.789 g cm-3)
(4 marks)
(e)
The reaction between ethanoic acid and ethanol can be represented by the following equation:
CH3COOH(l ) + C2H5OH( l )
CH3COOC2H5(l ) + H2O( l )
12.01g of ethanoic acid are treated with .61g of ethanol in the presence of a catalyst.
equilibrium at 298K, 5.04g of ethanoic acid are found to have reacted.
When the reaction reaches
(i) Name a suitable catalyst for this reaction in the forward direction.
(ii) Calculate the equilibrium constant, Kc, for the reaction at 298K.
(iii) What additional mass of ethanol would be required in order to use up a further 0.60g of ethanoic acid?
(iv) Would the addition of more of the same catalyst affect the value of K c? Explain.
(7 marks)
2.
(a)
Explain why phosphorus can form PC13 and PC15, while nitrogen can form only NC13.
(2 marks)
(b)
(i) What is the essential feature of a “redox reaction”?
(ii) Is the reaction below a “redox reaction” or an “acid-base reaction”? Explain.
CaO + SiO2  CaSiO3
(3 marks)
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HKALE
Chemistry (AL)
1995 Paper I
(c)
Manganate(VI) ions readily undergo disproportionation in aqueous solutions, except under very basic conditions.
Write a balanced equation for this disproportionation, and give the oxidation state of manganese in the reaction
product(s).
(3 marks)
(d)
(i) State whether the following hydrides would react with water under room temperature and atmospheric pressure.
If there is a reaction, give the balanced equation.
CH4
SiH4
H2S
HC1
(ii) Explain the difference in reactivity with water between CH4 and SiH4.
(iii) Explain the difference in reactivity with water between SiH4 and H2S.
(6 marks)
(e)
For each of the following species, draw a three-dimensional structure showing the bond electron pairs and lone electron
Pairs of the central atom. State the shape of the species in each case.
(i) IC14
(ii) SC12
(3 marks)
(f)
(i) Show the electronic configuration of a ground state Cr 2+ ion by filling in the appropriate boxes below.
1s
2s
2p
3s
3p
3d
4s
4p
4d
(ii) What is the highest possible oxidation state of chromium?
(iii) Give a chromium compound in which chromium is in its highest oxidation state.
(3 marks)
3.
(a)
Arrange the following carbocations in the order of increasing stability.
Explain your arrangement.
CH2
,
CH2
and
(3 marks)
(b)
Arrange the following carboxylic acids in the order of increasing acidity.
CICH2CO2H,
CICH2CH2CO2H
and
Explain your arrangement.
FCH2CO2H
(3 marks)
(c)
(i) Give the structure of the major product formed from the following reaction:
CH3
+ HBr
(ii) Outline a mechanism for the above reaction.
(Movement of electron pairs should be indicated by curly arrows.)
(3 marks)
(d)
(i) Give the reactants and conditions for the preparation of benzenediazonium chloride in the laboratory.
(ii) Write the structure of the product formed in the diazocoupling of naphthalene-2-ol with benzenediazonium chloride.
(iii) If an aqueous solution of benzenediazonium chloride is heated, a solid, which is soluble in dilute NaOH, can be
obtained.
Suggest a structure for the solid obtained and account for its solubility in dilute NaOH.
(5 marks)
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HKALE
(e)
Chemistry (AL)
1995 Paper I
Use equations to show how you would carry out the following conversions in the laboratory.
Give the reagent(s), conditions and structure of the intermediate compound(s) formed.
(i) (CH3)3COH
to
(CH3)3COCH2CH3
O
(ii) CH2=CH2
to
For each conversion,
O
COCH2CH2OC
(6 marks)
END OF SECTION A
SECTION B
COMPULSORY question.
4.
Write your answers in the spaces provided.
(a)
Devise an experiment to distinguish between KBr(s) and a mixture containing approximately 0% KCI(s) and 60%
KBr(s) by mass.
(3 marks)
(b)
(i) Describe the experimental procedure by which you would recrystallize a sample of impure benzoic acid.
(ii) How would you test the purity of the product obtained in (i)?
(4 marks)
(c)
You are provided with a Bunsen burner, a beaker, a thermometer and a set of quickfit apparatus.
Draw a labeled diagram to show how selected items from the above are set up for the determination of the boiling point
of propanone.
(3 marks)
(d)
Name the type of hazard warning label which should be displayed on a bottle containing propanone.
(1 mark)
(e)
For each of the volumetric analyses (i) to (iii), state whether an indicator is required.
the appropriate one from those given below:
If an indicator is required, select
litmus; methyl orange; phenolphthalein; potassium dichromate(VI) solution; starch solution
(i) ethanedioic and titrated with sodium hydroxide
(ii) Sulphuric(VI) acid titrated with aqueous ammonia
(iii) Iron(II) sulphate(VI) titrated with potassium manganate(VII)
(3 marks)
(f)
In the volumetric determination of chloride ions with silver nitrate(V) in neutral solutions, potassium chromate(VI) can
be used as an indicator.
(i) Explain the action of this indicator.
(ii) Why is this titration not carried out in strongly acidic or strongly basic conditions?
(3 marks)
(g)
Give the observations when (i) ammonia solution and (ii) sodium hydroxide solution are added dropwise, until in
excess, to aqueous solutions containing Pb2+ and Cu2+ ions respectively. These experiments are carried out at room
temperature.
(i) ammonia solution
(ii) sodium hydroxide solution
Pb2+(aq)
Cu2+(aq)
(3 marks)
END OF SECTION B
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HKALE
Chemistry (AL)
1995 Paper I
SECTION C
Answer ONE question only and write your answers in the AL(D) Answer Book.
Marks will be allocated approximately as follows:
Chemical knowledge
50%
Organization
30%
Presentation (including proper use of English) 20%
Equations, suitable diagrams and examples are expected where appropriate.
The examiners are looking for the ability to analyse, to evaluate and to express ideas clearly.
5.
Write an essay on hydrogen bonding.
(20 marks)
6.
7.
Write an essay on transition metal complexes, covering their stability, stereochemistry and the quantitative investigation
of their stoichiometry.
(20 marks)
Write an essay on the synthesis and the uses of poly(alkenes).
Your essay should include a mechanism for the formation of poly(alkenes) and the reasons why poly(alkenes) are widely
used.
(20 marks)
END OF PAPER
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