TEST CODE O22L2O2O

FORM TP 2OO7T74 MAY/JI.JNE 2OO7

CARIBBEAN EXAMINATIONS COUNCIL

ADVANCED PROFICIENCY EXAMINATION

CHEMISTRY

IJNIT2 - PAPER02

2 hours 75 minutes

Candidates are advised to use the first 15 minutes for reading thrcughthis paper carefully. Writing may begin during this time.

READ THE FOLLOWING INSTRUCTIONS CAREFTJLLY

1. This paper consists of NINE questions.

2. Section A consists of THREE questions, ONE question from each Module.AnswerALL questions. Answers for this section must be written in this booklet.

3. Section B consists of SD( questions. Answer ONLY THREE questions fromthis section, ONE question from EACH Module. Answers for this section mustbe written in the booklet provided.

4. ALL working MUST be CLEARLY shown.

5. The use of non-programmable calculators is permitted.

Materials provided:

o { Data Booklet. Graph Paper. Answer Booklet

Copyright @ 2006 Caribbean Examinations Council @

ozzrzozotcApElF z0o7 All rights reserved'

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SECTION A

AnswerALL questions in this section.

MODULE I

KINETICS AND EQUILIBRIA

1. An equilibrium is established on reacting bromine and chlorine in the solvent tetrachloromethane

at room temperature and pressure. The product of the reaction is bromine chloride, BrCl.

(a) (i) Write the equation for the reaction in this equilibrium system.

Ilmark]

(ii) Write the expression for the equilibrium constant, K".

[ 2 marks]

(b) (i) In an experiment set up to monitor this equilibrium, a reaction mixture is found

to contain 0.0389 mol of Br, ,0.0111 mol of Cl, and 0.0546 mol of BrCl.

Given that K at298 K for the system is 6.88, determine whether equilibrium is

attained in thl reaction mixture. Show all your working'

[ 3 marks]

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What TWO precautions should be taken to ensure that the experiment yields

accurate results?

[ 2 marks]

(iii) Suggest ONE safety measure that should be taken in this experiment.

(c) Under what experimental condition would the value of Kthat the reaction is endothermic?

[Lmark]

be greater than 6.90, given

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Total l0 marks

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MODIJLE 2

CHEMISTRY OF THE ELEMENTS

2. The halogens chlorine, bromine and iodine are found naturally as the metal halides in sea water

and salt deposits.

(a) Table 1 below gives the reaction products and observations for the reaction of the sodium

halides with concentrated sulphuric acid. Complete the table by filling in the missing ' i

products and observations.

TABLE 1: REACTION OF THE SODII]M HALIDES WITHCONCENTRATED ST]LPHIJRIC ACID

Halide Reaction product Observation

NaCl (i) Misty fumes

NaBr (iD

SO,

Brown fumes

(iii)

NaI (iv)

H,S

Purple fumes and blackprecipitate

(v)

[ 5 marks]

At room temperature and pressure, chlorine is a pale green gas, bromine a dark red

liquid and iodine a dark grey crystalline solid. Suggest ONE reason for the differences

in states of these three halogens.

tlmarkl

(c) Write a balanced equation for the reaction of chlorine with an excess of cold dilute

sodium hydroxide, and give the change in oxidation state of chlorine in the reaction.

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[ 4 marks]

Total L0 marks

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NOTHING HAS BEEN OMITTED

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3.

MODTILE 3

TNDUSTRY AND THB ETWIRONMENT

Industrial and agricultural activities have led to the pollution of freshwater lakes and rivers.

Phosphate (Pqt) levels above the acceptable range of 0.5 - 1.0 mg dm-3 are being detected

more frequently by environmentalists.

(a) (i) Suggest ONE possible source of phosphate ions found in polluted rivers and

lakes.

What observable feature of a pollutedconcentrations above 1.0 mg dm4?

Ilmark]

lake could result from phosPhate

Ilmark]

(iii) What process is responsible for the observed feature?

Ilmark]

Analysis of three water samples taken from a river is carried out using a

spectrophotometric method to determine the concentration of phosphate ions.

Use the calibration curve of absorbance reading versus concentration, provided

in Figure I on page 7, to estimate the concentration of phosphate ion in EACH

sample based on the results of the analysis. Write your answer in Table 2.

TABLE 2: RESIITTS OF ANALYSIS

[ 4 marks]

(ii)

(i)o)

Sample Absorbance reading Concentration of POn*

1

2

3

0.45

0.38

0.40

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7-

o 0.2 0.4 0.6 0.tConcentration POo3-(mg dm-t )

Figure 1: Calibration curve of absorbance versus concentration of POo'

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(ii) Calculate the average concentration of POo3- found in the three samples.

[ 2 marks]

(iii) Based on the results of the analysis, is the concentration of POo'- withinacceptable limits?

Ilmark]

Total l0 marks

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SECTION B

AnswerONE question fmm EACH module.

MODI.]LE 1

KINETICS AND EQUILIBRIA

Answer EITHER Question 4 OR Question 5.

Define the term 'buffer solution'. [ 2 marks]

A buffer solution can be made from a mixture of a weak acid and a salt of the acid.

Explain how this mixture functions to maintain pH on the addition of

(i) strong acid

(ii) strong alkali. [ 6 marks]

(c) The majorbuffer system used to control the pH of the blood is the carbonic acid (H2CO3)

- bicarbonate (HCO'-) buffer system below.

4. (a)

(b)

Cor(ac) + Hro(l) s HrCor(ac)

HrCor(ag) * n-(uq) + HCO,- (at)- Equation 1

- Equation 2

(d)

(D a) During periods of strenuous exercise there is a build-up of carbon dioxidein the blood. Explain what effect this has on the buffer system by makingreference to Equations I and 2. [ 2 marks]

b) This effect can be reversed by breathing more deeply and more quicklyduring exercise. Explain how this is possible. [ 4 marks]

Abuffer solution is made up of 0.025 mol dm-3 of ethanoic acid, CII.COOH, and 0.010mol dm-3 sodium ethanoate, CH3COONa. The K" for ethanoic acid is I.75 x lO-s moldm-3.

(i) Write the expression for the Ku of ethanoic acid. I I mark ]

(ii) Use the expression in (d) (i) above to calculate the pH of the buffer.

[ 5 marks]

Total20 marks

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J. Table 3 below gives data obtained during an investigation of the rate of hydrolysis of a halo-genoalkane, R - X, with NaOH (aq).

R-X+NaOH+ R-OH +Nd(.

TABLE 3: DATA ON THE RATE OF ITYDROLYSIS OFAHALOGENOALKANE WITH NaOH

Experimentnumber

Initial IR-XI/mol dm-3

Initial [NaOH(aq)]/mol dm-3

Rate of product(ROH) formation

mol dm-3 s-l

1

2

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45

6

6x 10-3

6x1036x l0-3I x 10-3

2xl}a3 x l0-3

1 x l0-32x IF3 x 10-3

6 x 10-3

6 x 10-3

6 x 10-3

3 x 10-3

6 x l0-39x1f3

0.5 x 10-3

1 x 10-3

1.5 x l0-3

Determine the order of the hydrolysis reaction with respect to

(i) R-x(iD NaOH.

[ 4 marks]

Deduce the overall order of the reaction and construct the rate equation for the hydrolysis.

[ 2 marks]

Calculate the value of the rate constant and state the units. [ 3 marks]

Suggest a possible mechanism for the hydrolysis of the halogenoalkane and use therepresentative structure below to illusfrate the steps involved.

RI

,ri'l rt I x

H[ 3 marks]

(e) Use collision theory to state and explain the effects of EACH of the following on therate of a reaction:

(D Temperature [3marks]

(ii) Concentration [3marks]

(iii) Surface area [ 2 marks]

Total20 marks

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(a)

(b)

(c)

(d)

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MODULE 2

CHEMISTRY OF THE ELEMENTS

Answer EITIIER Question 6 OR Question 7.

The physical and chemical properties of the Period 3 oxides and chlorides are determined by

their strucnrre, bonding and reaction with water.

(a) Copy Table 4 in your answer booklet. Complete Table 4 by writing in the type ofbonding for EACH compound.

TABLE 4: COMPOUI\D AND TYPE OF BONDING

Compound Type ofbonding

Naro

Mgo

Al2o3

Alct3

sicl4

PC15

[ 6 marks]

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(b) State the acid/base character of

(i) Meo

(ii) Al2o3.

(i) NarO

(ii) sicl4

(iiD PCls

(c) Write balanced equations to show the reaction between water and EACH of the followingPeriod 3 compounds:

[Lmark]

[Lmark]

[ 2 marks]

[ 2 marks]

[ 2 marks]

(d)

(e)

Give the approximate pH of the solution formed from the reactions in (c) (i) and (c) (ii)above. [ 2 marks]

SiClo is a liquid at room temperature and pressure but SiO, is a solid with a high meltingpoint. Explain the above observations in terms of the structure and bonding of thesilicon compounds. [ 4 marks]

Total20 marks

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7. (a)

(b)

(c)

(d)

Describe the trend in electrical conductivities of the Group [V elements and relate it totheir physical structure. [ 2 marks]

state the type of bonding found in EACH of the following Group rv dioxides.

(i) co,

(ii) sio2

(iii) GeO,

(iv) PbO2

Ge4* + 2e; -+ Ge2*

Sna*+ 2e- + Sn2*

Pb4*+ 2e- + Pbz*

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Eo = - 1.6VE0 = +0.15VEo = +1.8V

ILmark]

Ilmark]

ILmark]

Ilmark]

Classify the acid/base character of the Group IV dioxides and explain how it relates tothe type of bonding. [ 4marks]

Use the following standard electrode potentials to comment on the relative stability ofthe +4 and+2 oxidation states of Ge, Sn and Pb.

[ 2marks]

(e) Sn2* ions will reduce orange CrrO.,z- to green Cf* but Pb2* ions will not. Discuss thisstatement with reference to standard electrode potentials. Use suitable half-equationsto illustrate your answer. [ 4 marks]

Silicon terachloride (SiClo) fumes and forms a white precipitate with water, while carbontetrachloride (CClo) is immiscible with water- Explain these observations and write abalanced equation for the reaction occurring. [ 4 marks]

Total20 marks

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MODITLE 3

INDUSTRY AND THE EIWIRONMENT

Answer EITHER Question 8 OR Question 9.

Crude oil is a complex mixture of hydrocarbons which are separated during refining.

(a) (i) What is the name of the process which separates crude oil into its various

components?

(ii) Explain the basis on which this separation occurs.

Ilmark]

[ 2 marks]

The combustion of fossil fuels obtained from the separation of crude oil produces oxides

of nitrogen and sulphur in addition to carbon dioxide.

(D Using NO, and SO, , explain how these gases are produced. Illustrate youranswer wifh balanced equations. [ 6 marks]

(ii) What are the environmental implications of releasing these gases into the

atrnosphere? t 2 marksl

(c) Leaded compounds and carbon monoxide are emitted in vehicular exhaust.

(D Why are leaded compounds and carbon monoxide considered pollutants?

[ 2 marks]

(ii) Explain the source of PbO and carbon monoxide in vehicular exhaust.

[ 2 marks]

(iii) Give ONE step taken to reduce tfre amount of lead pollution caused by usingpetrol. Ilmark]

(d) Suggest FOUR considerations that must be taken into account when deciding the locationof an oil refinery. [ 4 marks]

Total20 marks

(b)

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(a) In 1995 the Nobel prize for Chemistry was won by three scientists for their work on thedepletion of stratospheric ozone in the upper atmosphere.

(i) 'Write equations to show the formation of stratospheric ozone and how ozone

(b)

(c)

levels are kept constant naturally.

(ii) Explain the biological significance of stratospheric ozone.

propellans.

(iD State TWO OTIIER uses of CFCs or Freons.

Give FOUR rquons for ozone being considered a pollutant in the lower afinosphere.

[ 4 marks]

Some CFCs are sold under the trade name Freons and are used as aerosol propellants.

(i) State THREE reasons, based on their properties, for the use of CFCs as aerosol

[ 6 marks]

[ 3 marks]

[ 3 marks]

[ 2 marks]

(d) Give TWO reasons for CFCs being so destructive to the ozone layer. [ 2 marks]

Tiotal20 marks

END OF TEST

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