FORM TP 2004180TEST CODE 02212020

MAY/JUNE 2004

CARIBBEAN EXAMINATIONS COUNCIL

ADVANCED PROFICIENCY EXAMINATION

CHEMISTRY

UNIT 2 - PAPER 02

2 hours 15 minutes

iCandidates are advised to use the first 15 minutes for readingthrough this paper carefully.

READ THE FOLLOWING INSTRUCTIONS CAREFULLY

1. This paper consists of NINE questions.

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

3. Section B consists of SIX 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:

• A Data Booklet• Graph Paper• Answer Booklet

Copyright © 2003 Caribbean Examinations Council.

2

SECTION A

Answer ALL questions in this section.

MODULE 1

1. Two substances, A2 and B2, react according to the equation:

A2 + B2 ---* 2 AB

The kinetics of the reaction are studied and presented in Table 1.

TABLE 1: DATA ON THE REACTION BETWEEN A2 AND B2

Expt. #Initial , [A2]/mol dm

Initial [B2]/mol dm-

Initial Rate of Formationof AB/mol dm s

1 0.1 0.1 0.00141

2 0.1 0.2 0.00138

3 0.2 0.1 0.00290

4 0.3 0.3 -

(a) What variable MUST be kept constant in order to determine the order of reaction withrespect to A2?

[ 1 mark ]

(b) What variable is manipulated in determining the order of reaction with respect to B2?

G[ 1 mark]

(c) What is the order of reaction with respect to

(i) A2?

[1 mark]

(ii) B2?

[ 1 mark ]

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3

(d) Estimate a value for the initial rate of formation of AB in Expt. 4.

[ 1 mark ]

(e) Write a rate equation for the reaction AND use the equation to calculate the value ofthe rate constant, k, for the reaction.

(i) Rate equation

[ 1 mark]

(ii) Calculation of k

[ 1 mark ]

(f) Propose a mechanism for the reaction that is consistent with its kinetics.

[ 3 marks]

Total 10 marks

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MODULE 2

2. (a) Haemoglobin is a complex ion containing Fe 2+ as the central metal cation. Thestability constant for the haem-CO system is higher than the constant for the haem-O2system. Explain the effects on the human body of exposure to high levels of carbonmonoxide.

[ 4 marks]

(b) (i) Complete Table 2 by writing the observation made when aqueous ammonia isadded to copper (II) nitrate solution.

TABLE 2: REACTION OF TRANSITION METALS WITH NH3(aq)

Test Observation

Aqueous ammonia is addeddropwise to a solution of

II i il i icopper ( ) n trate unt t spresent in excess.

[ 4 marks]

(ii) Write a balanced equation to represent the overall reaction occurring in (b) (i).

[ 2 marks]

Total 10 marks

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MODULE 3

3. The cycling of nitrogen through the environment is shown in Figure 1.

N2

Fossil fuel combustionlightning

(i)

Nitrifying bacteria

Animal protein

Figure 1. Nitrogen Cycle

(a) Using the data in Figure 1, state the nitrogen base species that are present at the follow-

ing sites of the nitrogen cycle:

(i)

(ii)

(iii)

(iv) Write the balanced equation for the conversion of (i) to (ii).

[ 1 mark ]

[ 1 mark]

[ 1 mark ]

[ 2 marks]

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(b) The chromotropic acid method is a recommended method for the determinationof nitrate-nitrogen (NO3 - N) between the concentration range 0.1 to 5 mg NO3 - N /I inwaste water. The underlying principle is based on the fact that two moles ofNO3 (nitrate) react with one mole of chromotropic acid to form a yellow reactionproduct with maximum absorbance at 410 nm.

Figure 2 shows the calibration curve for the determination of nitrate-nitrogen concen-tration using the chromotropic acid method.

NOTE: Chromotropic acid: 4.5 dihydroxy - 2, 7-napthalene disulfonic acid

0.4

0.35

ea 0.30

0.25

0.2

0.15

0.1

0.05

0

- - - - - - - - - - -- - - - - ------ ---

-it.. ^ --. - ...... ...................

----------- --

HiH

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75

Concentration of nitrate -nitrogen /(mg/1)

Figure 2. Calibration curve

(i) Use Figure 2 to determine the concentration of NO3-N for EACH of the FOURsamples of effluent in Table 3. Write your answers in Table 3.

TABLE 3

Samplenumber

Absorbanceat 410 mm

Concentration ofNO3- N in mg/l

1 0.20

2 0.22

3 0.23

4 0.25[ 4 marks]

Determine the average NO3-N concentration for the four samples in Table 3.

1 mark ]

Total 10 marks

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SECTION B

Answer THREE questions from this section , ONE question from EACH module.

MODULE I

Answer EITHER Question 4 OR Question 5.

4. The solubility product , K,p, of silver chloride at 25°C is 1.8 x 10-10 mol2dm-6. Silver chlorideprecipitates out of solution if the product of the ion concentration of the salt in solutionexceeds its solubility product.

(a) Write an expression for the solubility product, Ksp, of silver chloride. [ 1 mark ]

(b) When 1.0 cm3 of 0.001 mol dm -3 silver nitrate is added to 1.0 dm3 of 0.001 mol dm -3sodium chloride at 25°C, will a precipitate of silver chloride be produced? Explainyour reasoning. [ 5 marks]

(c) In an experiment to determine the solubility product of calcium hydroxide, asaturated solution of calcium hydroxide at 25°C is carefully filtered into a clean dryflask. 25.0 cm3 of this solution are pipetted into a conical flask and three drops ofphenolphthalein indicator added. The solution needs 11.50 cm3 of 0.10 mol dm-3hydrochloric acid for neutralisation.

(i) Explain how the results of the experiment can be used to obtain a value for thesolubility product of calcium hydroxide at 25°C. [ 4 marks]

(ii) Calculate a value for the solubility product of calcium hydroxide at 25°C.[ 5 marks]

(d) Explain what happens when the filtered solution in (c) is added to a concentratedsolution of calcium chloride. [ 5 marks]

Total 20 marks

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5. Colourless N204 (g) decomposes on warming to give brown NO2 (g). 0.10 mol of N204 (g) isplaced in a 1.0 dm3 bulb and sealed and the bulb is heated to 100°C. When equilibrium isestablished, 0.035 mol of N204 (g) is found to be present.

(a) State TWO characteristics of a system in dynamic equilibrium . [ 2 marks]

(b) Write an equation for the equilibrium that exists between N204 (g) and NO2 (g).[1 mark

(c) (i) Predict what may be observed when the bulb is heated to 200°C.[ 1 mark ]

(ii) Give a reasoned argument for your answer in (c) (i). [ 3 marks]

(iii) Predict what may be observed when the pressure on the system is increasedfrom 1 atmosphere (atm) to 2 atm. [ 1 mark ]

(iv) Give a reasoned argument for your answer in (c) (iii ). [ 3 marks]

(d) (i) 0.40 mol of N204 is introduced into the system at 100°C. What is the effect onthe equilibrium constant, K°? [ 1 mark ]

(ii) Explain your answer in (d) (i). [ 2 marks]

(e) Write an expression for K° for the system AND calculate the value of K° at 100°C.[ 6 marks]

Total 20 marks

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MODULE 2

Answer EITHER Question 6 OR Question 7.

6. (a) The oxides and chlorides of the elements Na to Ar show variations that demonstrateperiodic patterns or trends. By reference to named examples, explain the periodicvariation in the oxidation numbers of the oxides of the elements. [ 5 marks]

(b) Write a balanced equation for the reaction of EACH of the following with water:

(i) Metal chloride [ 2 marks]

(ii) Non-metallic oxide [ 2 marks]

(c) Aluminium chloride is a metallic chloride, yet its solution is acidic.

(i) How is this observation different from that of chlorides of Group I andGroup II elements? [ 1 mark ]

(ii) Suggest an explanation for the acidic nature of the aluminium chloride solution.

[ 2 marks]

(d) (i) Explain the trend in acid/base behaviour of the oxides of the elements of Period 3in terms of structure and bonding. [ 4 marks]

(ii) Write a balanced equation to represent EACH of the following:

a) Acidic nature of a selected oxide of the elements of Period 3

b) Basic nature of a selected oxide of the elements of Period 3

[ 4 marks]

Total 20 marks

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I 7. (a) The Group IV elements vary in properties from non-metallic to metallic down thegroup, but the tetrachlorides are all covalent compounds.

(i) Describe the bonding in a named Group IV tetrachloride AND explain why allof the tetrachlorides are covalent compounds. [ 4 marks]

(ii) Silicon tetrachloride is stable at room temperature with respect to dissociationinto the constituent elements, but lead tetrachloride decomposes into lead (II)chloride and chlorine. Account for this difference in stability. [ 3 marks]

(b) SiCl4 can be converted to an intermediate compound, SiC13OH, on reaction with water.

(i) Write an equation for the formation of the intermediate compound, SiC13OH.[ 2 marks]

(ii) Silicon had an electronegativity value of 1.8 while chlorine has a value of 3.0.Explain how this difference promotes the reaction of SiCl4 with the watermolecule. [ 4 marks]

4(iii) The final product of the reaction between SiC14 and water can yield hydrated

silicon (IV) oxide. Name the process that occurs to produce hydrated sili-con (IV) oxide. [ 1 mark ]

(c) Ceramics are used in applications because of their chemical durability. Some propertiesof ceramics include hardness, heat resistance, corrosion resistance, and super conductivityat high temperatures.

(i) Explain how the structure and bonding of silicon (IV) oxide make it suitableas a base for ceramics with the above properties. [ 4 marks]

(ii) Comment on the heat and corrosion resistance of a ceramic based ongeranium (IV) oxide, relative to one based on silicon (IV) oxide.

[ 2 marks]

Total 20 marks

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MODULE 3

Answer EITHER Question 8 OR Question 9.

8. Aluminium is extracted from its ore (bauxite) by electrolysis. Bauxite is the generic termapplied to a naturally occurring mixture of minerals rich in aluminium oxides.

Figure 3 is a diagram showing the electrolysis of alumina (impure bauxite).

Figure 3. Electrolysis of alumina

(a) Identify EACH of the regions indicated by (i) - (iv) in Figure 3. [ 4 marks]

(b) Comment on the MAIN reason for mixing the bauxite with the electrolytic mixture.

(c)

(d) '

State the MAIN reason why the anode has to be replaced periodically.

Name the element discharged at EACH of the following:

(i) Cathode

(ii) Anode

[ 2 marks]

[ 1 mark]

[ 1 mark ]

[ 1 mark ]

(e) Show by using balanced half equations the electrolytic process at EACH of the following:

(i) The cathode [ 2 marks]

(ii) The anode [ 2 marks]

(f) Aluminium is now a very important metal that is used widely in the home and inindustry. For example, it is used in the manufacture of pots and pans, to wrap prematurebabies, as a coating of suits for fire fighters, and in car headlights. .

By refering to TWO of the uses above , discuss the seemingly contrasting propertiesof aluminium. [ 7 marks]

Total 20 marks

(_(1 nXT T(1 T TsYT DA (--I:;

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9. The petroleum and petrochemical industries have proven to be both a benefit and a hazard.The industries, however, have been challenged by more rigid environmental regulations inrecent years.

(a) (i) Describe the process of petroleum refining. [ 5 marks]

(ii) Identify FOUR benefits that are obtained from the process. [ 5 marks]

(b) Discuss TWO reasons for the enforcement of more rigid environmental regulations onthe industries. [ 5 marks]

(c) The release of hydrocarbons into the atmosphere is considered one of the contributingfactors to the formation of photochemical smog.

(i) Explain the meaning of the term photochemical in relation to the formation ofsmog. [ 1 mark ]

(ii) Give TWO sources of hydrocarbons in the atmosphere. [ 2 marks]

(iii) Suggest ONE factor that will lead to maximum photochemical activity in theatmosphere. Explain your answer. [ 2 marks]

Total 20 marks

END OF TEST

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