heep woh collegeaerodrive.ccchwc.edu.hk/~lck/ckraylau/alchem/1011almock1.pdf · 2011. 1. 26. ·...

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

CCC HEEP WOH COLLEGE 2010 – 2011 MOCK EXAMINATION

F.7 AL CHEMISTRY PAPER I 8:30am – 11:30am (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 THREE sections in this paper, Section A, Section B and Section C.

3. Section A carries 60 marks, Section B carries 20 marks, and Section C carries 20 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. Answer ONE question in Section C. Answers are to be written in Supplementary Answer Sheets.

6. 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

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

Question 1 [9 marks]

(a) (i) In the graph given below, sketch the variation in first ionisation enthalpy from aluminium to

calcium.

(ii) Explain briefly your sketch.

(5 marks)

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(b) Sodium hydride contains hydrogen in the form of an anion. The substance is a crystalline

substance with a 6:6 coordination.

(i) Draw a unit cell showing the structure of sodium hydride.

(ii) Give one piece of evidence to show that hydrogen exists as anions in sodium hydride.

(iii) Calculate the internuclear distance of Na+H–, given that the density of sodium hydride is

1.40 g cm-3.

(4 marks)

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(a) Consider the following data:

/ kJ mol-1

Enthalpy change of hydration of Mg2+ –1890

Enthalpy change of hydration of Ba2+ –1275

Enthalpy change of hydration of OH– –550

Lattice enthalpy of Mg(OH)2 –2995

Lattice enthalpy of Ba(OH)2 –2320

(i) Explain why the sign of the enthalpy change of hydration is always negative.

(ii) Calculate the enthalpy of solution of Mg(OH)2(s) and Ba(OH)2(s).

(iii) Use the data to explain the trend in the solubility of Group II hydroxides.

(5 marks)

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(b) An aqueous solution of the compound [CoCl2(NH3)4]Cl gave the following transmittance

spectrum.

(i) From the above spectrum, deduce the colour of the solution.

(ii) The solution contains the complex ion [CoCl2(NH3)4]+.

(I) What is the oxidation number of cobalt in this complex ion?

(II) Name this complex ion.

(III) Write down the electronic configuration of cobalt in this complex in terms of orbitals.

(4 marks)

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(a) The diagram below shows a syringe containing a gaseous mixture of N2O4(g) and NO2(g) at

equilibrium at room temperature.

N2O4(g) 2NO2(g)

colourless brown

(i) The plunger is quickly pulled from mark A to mark B at time t1 while the temperature of the

mixture is kept constant.

(I) State the expected observation(s) and explain your answer.

(II) Sketch on the given graph to show the variation in the concentration of NO2(g) in the

mixture until the new equilibrium is attained.

(ii) Draw the electronic structure of a N2O4 molecule.

(5 marks)

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(b) Account for the following:

(i) The boiling point of NH3 is –36°C, but that of PH3 is –87°C.

(ii) Unlike the other halogens, fluorine does not disproportionate in water.

(4 marks)

(c) Answer the following multiple-choice questions:

(i) When sulphur dioxide and oxygen react the following equilibrium is established.

2SO2(g) + O2(g) 2SO3(g)

The equilibrium constant for the reaction is 3300 at 630°C and 21 at 850°C.

Which of the following combination is correct for the reaction?

Sign of H Product yield as temperature increases

A. + decreases

B. + increases

C. – decreases

D. – increases

Answer :

(ii) Which of the following concerning fullerenes and ice is/are correct?

(1) Both are compounds.

(2) Both have simple molecular structure.

(3) The melting point of fullerenes is usually lower than that of ice.

A. (1) only

B. (2) only

C. (1) and (3) only

D. (2) and (3) only

Answer :

(iii) Hund’s rule states that

A. it is impossible to define both the position and momentum of an electron

simultaneously.

B. electrons occupy orbitals in the order of increasing energy.

C. electrons occupy degenerate orbital singly with parallel spins before spin pairing

occurs.

D. the energy of an electron in an atom is quantised.

Answer :

(3 marks)

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Read the passage below and answer the questions that follow:

A dry ice bomb

A dry ice bomb is a bomb-like object. The components for making a dry ice bomb are dry ice, water

and a plastic container e.g. bottle. The dry ice is broken into small pieces and inserted into the

bottle. Then, enough water is poured in to just cover the dry ice. After that, the bottle is capped

tightly and it will explode 10-30 seconds later. The explosion of dry ice bomb can create a high

bursting pressure and sound. Therefore, dry ice bomb is considered to be very dangerous and

making this bomb is illegal in some countries.

Dry ice

Dry ice is solid carbon dioxide. At normal atmospheric pressure and temperature it undergoes

sublimation, resulting in a great increase in volume. Carbon dioxide is colourless, odourless and

non-flammable. It is slightly acidic when dissolving in water. The surface temperature of a block of

dry ice is 78C. When dry ice is in contact with water in a capped bottle, it becomes warm and

sublimates to a gas immediately. Then, pressure builds up quickly inside the capped bottle until the

strength of the bottle cannot withstand the pressure of the gas, which results in the explosion of the

bottle.

Dry ice is an ideal material for refrigeration to preserve food such as ice-cream and biological

samples. Moreover, dry ice can be used in theatres and haunted houses for dramatic effects

because it can create fog. Unlike most artificial fogs made by fog machines, the fog from dry ice

hovers around the ground rather than rising like smoke.

(a) (i) With reference to the Valence Shell Electron Pair Repulsion theory, predict the shape of a

carbon dioxide molecule.

(ii) State and explain whether carbon dioxide molecule is polar or not.

http://en.wikipedia.org/wiki/Fog_machine

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(b) (i) Is the explosion of dry ice bomb a physical change or a chemical change? Explain your

answer briefly.

(ii) Explain briefly why the rate of sublimation increases when dry ice is in contact with water.

(c) (i) Write an equation to show that carbon dioxide is slightly acidic when dissolving in water.

(ii) Show that carbon dioxide gas is denser than air by calculating the relative molecular

masses of air and carbon dioxide.

(Hints: air consists of 78% of nitrogen gas and 22% of oxygen gas.)

(d) Explain why dry ice is preferred to normal ice for freezing and preserving ice-cream.

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Alanine, CH3CH(NH2)COOH, and valine, (CH3)2CHCH(NH2)COOH, are both -amino acids that occur

naturally.

(a) Draw the zwitterions structure of alanine.

(b) Draw the structures of two different dipeptides that could be formed from the reaction of one

molecule of alanine with one molecule of valine.

(c) Aqueous sodium hydroxide was added to valine. Draw the structure of the ion formed.

(d) Hydrochloric acid was added to alanine. The resulting solution was concentrated and crystals

of a compound B were separated. Draw the displayed formula of compound B.

(e) Phosphorus pentachloride, PCl5 was added to alanine forming an acyl chloride. The acyl

chloride was then reacted separately with methanol and with ammonia. Draw the structure of

the acyl chloride and the organic compounds formed from the acyl chloride.

Acyl chloride Product with methanol Product with ammonia

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(f) Compounds C and D are also -amino acids.

Compound C has the molecular formula C4H9NO3.

Compound D has the molecular formula C6H14N2O2.

Suggest structures for amino acids C and D.

C D


(a) Answer the following multiple-choice questions:

(i) Which of the following molecules does NOT exhibit optical isomerism?

A. Br

Br B.

Br

Br

C.

CH(OH)CH 3 D.

CHBrCHO

Answer :

(ii) Which of the following is most reactive as a nucleophile?

A. NaOH

B. CH2CH2NH2

C. CH3CH2ONa

D. CH3COONa

Answer :

(iii) Arrange the nitrogen atoms (Na, Nb and Nc) of histamine in order of their decreasing basic

strength.

A. Na, Nb, Nc

B. Nb, Nc, Na

C. Na, Nc, Nb

D. Nc, Na, Nb

Answer :

(3 marks)

HNc

Nb NaH2

histamine

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(b)

Compound E can be manufactured from 2-oxopropanoic acid in three stages as shown below:

(i) Identify the reagents and conditions required for stage 1.

(ii) Identify the reagents required for stage 2.

(iii) State the name of the mechanism in stage 2.

(iv) Deduce the other product formed in stage 3.

(v) A typical yield of compound E from 2-oxopropanoic acid is 30%.

Calculate the mass of compound E you would expect to produce from 10 kg of

2-oxopropanoic acid. Give your answer to two significant figures. Show your working.

(7 marks)

End of Section A

C=C

H

H

COOCH3

CN

Compound E

Compound

E CH3CCOOH

O Stage 1

CH3CCOOCH3

O Stage 2

CN

CH3COH

COOCH3 Stage 3

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


(a) Mass spectrometry is an important analytical technique. It can be used to help to distinguish

between isomers such as 1-chloropropane, CH3CH2CH2Cl, and 2-chloropropane, CH3CHClCH3.

(i) (I) What are the formulae of the molecular ions of 1-chloropropane which give rise to

the following peaks?

M peak: ______________________________________________________________

M+2 peak: ______________________________________________________________

(II) In the mass spectrum of 1-chloropropane what are the relative heights of the M and

M+2 peaks?

(ii) Fragment ions can be used to distinguish between 1-chloropropane and 2-chloropropane.

Give the formula of a fragment ion that would be formed from 1-chloropropane but not

from 2-chloropropane.

(3 marks)

(b) A mixture contains equal amounts of X, Y and Z.

OH NH2

CH3

Br

X Y Z

b.p. 182C b.p. 184C b.p. 184C

Outline a chemical method to separate X, Y and Z from each other.

(4 marks)

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(c) Amides are generally prepared by reacting equimolar amounts of an amine and an acid

halide. Calculate:

(i) the mass (in grams) of Y required to react with 4.0 g of benzoyl chloride (C6H5COCl), and

(ii) the percentage yield of the same reaction if 4.0 g of the amide product is obtained.

(3 marks)


(a) The standard electrode potential of Fe3+(aq) + e- Fe2+(aq) is +0.77V.

(i) Define the standard electrode potential of Fe3+(aq) + e- Fe2+(aq).

(ii) Complete the diagram below of apparatus that would be used to measure the standard

electrode potential of Fe3+(aq) + e- Fe2+(aq).

H2(g)

H+(aq)

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(iii) A standard cell is set up using the following redox equilibria.

Fe3+(aq) + e- Fe2+(aq) E = +0.77V

I2(aq) + 2e- 2I-(aq) E = +0.54V

Construct an equation for the overall cell reaction that takes place. What is the standard

cell potential of this cell?

(6 marks)

(b) The percentage of copper in brass can be estimated by titration.

The brass is completely reacted with concentrated nitric acid. The solution is then neutralised

and an excess of KI(aq) is added. This mixture is then titrated with Na2S2O3(aq).

Describe how you would carry out this titration.

(4 marks)

END OF SECTION B

Section C: Answer ONE question only and write your answers in the ANSWER SHEETS provided.

Marks will be allocated approximately as follows:

Chemical knowledge 50%

Organization 30%

Presentation (including use of language) 20%

Equations, suitable diagrams and examples are expected where appropriate.

Mr. Lau is looking for the ability to analyse, to evaluate to express ideas clearly.


Write an essay on thermochemistry. Your essay should include experimental and theoretical

consideration, together with the application of thermochemical data.


Write an essay on the chemistry of hydroxy-compounds (ROH), where R can be phenyl (C6H5) or

alkyl (CnH2n+1).

END OF PAPER

heep woh collegeaerodrive.ccchwc.edu.hk/~lck/ckraylau/alchem/1011almock1.pdf · 2011. 1. 26. ·...

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