AL-CHEM_97-06_Chemistry_and_Society.pdf

AS/AL-CHEM (1997-2006) Chemistry and Society

1

NOTE: Questions with an ‘*’ are NOT required by the HKDSE syllabus. They are included so as to enrich your knowledge and

broaden your understanding in chemistry.

1997-AL-CHEM 1 6. (a) (i) Vegetable oils (e.g. peanut oil) can undergo the following chemical reactions to give useful solid

products P and Q.

vegetable oil

excess H2/pt

NaOH(aq)heat

P

Q

Give one use each for P and Q. Suggest a possible structure for P.

*(ii) What is meant by the “iodine value” of a fat/oil?

(3 marks)

Mark Scheme .............................................................................................................................................. ��

6. (a) (i) P is a hardened oil, e.g. margarine (or butter substitute). ½

Q is a soap. ½

Possible structure of P: 1

CH2

CH

CH2

O

O

O

COC9H19

COC11H23

COC11H23 (Any correct structure of a saturated triglyceride)

(ii) Iodine value: The no. of grams of iodine that reacts with 100 g of the fat/oil. 1

[3]

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6. (b) Saponification of 1 mol of fat G with NaOH(aq) produces 1 mol of a triol C3H8O3, 2 mol of CH3(CH2)16CO2-Na

+

and 1 mol of CH3(CH2)14CO2-Na

+.

(i) If G is optically active, suggest its structure. Explain.

(ii) If G is optically inactive, suggest its structure.

(iii) What is the minimum number of moles of base required for the complete saponification of 1 mol of G?

(4 marks)

Mark Scheme .............................................................................................................................................. ��

6. (b) (i)

CH2

*CH

CH2 O

O

O

C

O

C

C

O

O

(CH2)16CH3

(CH2)16CH3

(CH2)14CH3

1

Because G contains an asymmetric / chiral / stereogenic centre, indicated by *.

½,½

(ii)

CH2

CH

CH2 O

O

O

C

O

C

C

O

O

(CH2)16CH3

(CH2)14CH3

(CH2)16CH3

1

(iii) three moles of base (e.g. NaOH / KOH)

1

because hydrolysis of 1 ester group requires 1 mole of OH- 1

[4]

� EEEExam Practice Functional groups Do Brilliantly �

2

1998-AL-CHEM 1

6. (a) Most natural fats and oils are mixed glycerides, and may be characterised by their ‘iodine value’, two examples

of which are shown below:

Fat/oil Iodine value

Butter fat 30

Corn oil 120

(i) Draw the structure of a typical natural fat or oil.

*(ii) Assuming that butter fat and corn oil glycerides have similar relative molecular masses, suggest what

information about their chemical structures may be deduced from the iodine values in the above table.

(3 marks)

6. (b) With the help of formulae, outline the chemical reaction involved in each of the following processes:

(i) saponification of an animal fat

(ii) hardening of a vegetable oil

(2 marks)

Mark Scheme .............................................................................................................................................. ��

6. (a) (i) CH2

CH

CH2

OCOC15H29

OCOC15H27

OCOC15H31

(many possible answers, including shorter chains of fatty acids)

1

(ii) The iodine value provides relative information on the degree of unsaturation / number of

carbon-carbon double bonds in the fatty acid chains.

In this case, corn oil fatty acid chains have more unsaturated centers than butter.

1

1

[3]

(b) (i) fat / oil NaOH(aq) reflux

sodium salt of fatty acid (soap) + glycerol

RCO2Na +

CH2OH

CHOH

CH2OH

(ii) C7H15CH=CHCH2CH=CHCH2CO2R

H2/PtC13H27CO2R

1

[2]

1998-AL-CHEM 2

5. (b) Chlorofluorocarbons (CFCs) such as CFCl3 and CF2Cl2 have been used as refrigerants, aerosol propellants, and

blowing agents in foam plastic manufacturing. There is evidence showing that the release of CFCs into the

atmosphere is a major cause of ozone depletion in the stratosphere.

(i) State the beneficial function of ozone in the stratosphere.

(ii) With the help of equations, show how CFCs, like CF2Cl2, can cause ozone depletion in the

stratosphere.

(iii) Why is ozone a pollutant in the atmosphere?

(5 marks)


3

� Marking Scheme Mark

5. (b) (i) acts as a filter for harmful ultraviolet radiation from the sun 1/0

(ii) In the stratosphere, CFCs absorb UV radiation to give Cl•. ½

CF2Cl2

hv

or UVCF2Cl + Cl

½

The following free radical chain reaction then occurs and ½

each Cl• produced can cause the removal of a large no. of O3. ½

Cl• + O3 → ClO• + O2 ½

ClO• + O3 → Cl• + 2O2 ½

or, Cl• + O3 → ClO• + O2

O3 → O2 + O

ClO• + O → Cl• + O2

O3 reacts with unburnt HCs and NO2 (from automobile exhaust) giving rise to the formation of

photochemical smog. ½,½

or, O3 is toxic / has adverse effects on the respiratory system. (1)

5 marks

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6. (a) Consider the structures of the two synthetic polymers shown below:

CH2CH2

npoly(ethene)

HN(CH2)6NHCO(CH2)4CO

n

nylon-6,6

(i) Suggest an explanation for the fact that nylon-6,6 has a higher tensile strength than poly(ethene).

(ii) Briefly explain why aqueous acids can more readily attack nylon-6,6 than poly(ethene) inducing

degradation.

(iii) Apart from acidic conditions, state one other condition under which nylon-6,6 degrades more readily

than poly(ethene).

(5 marks)

(b) (i) The installation of catalytic converters onto car exhaust systems can reduce the emission of three major

classes of air pollutants. Name the three classes of pollutants.

(ii) With the help of equations, briefly describe how a catalytic converter reduces the emission of these

pollutants.

(4 marks)

Mark Scheme .............................................................................................................................................. ��

6. (a) (i) The interaction between polymer chain of PE is van der Waals’ forces 1

while that between Nylon 6.6 is hydrogen bond.

½

The higher tensile strength of nylon is due to its stronger intermolecular attraction. ½

(ii) C—C linkage in PE is non-polar. ∴ not readily attacked by acids/has no reaction with acids. 1

The amide linkage in nylon hydrolyse in acids to give –NH3+ and COOH groups

causing shortening of the chain. ½,½

(iii) alkaline conditions / enzyme 1

5 marks

Can you draw the

Lewis structure of O3?


4

6. (b) (i) nitrogen oxides, carbon monoxide, (unburnt) hydrocarbons 3×½

(ii) The converter contains the metal catalysts Rh/Pt/Pd which catalyse the following reactions. ½

Air is introduced into the converter to oxidize CO and unburnt HCs to CO2. ½

2NO(g) + 2CO(g) → N2(g) + 2CO2(g) [catalysed by Rh] ½

2CO(g) + O2(g) → 2CO2(g) [catalysed by Pt /Pd] ½

C7H16(g) + 11O2(g) → 7CO2(g) + 8H2O(l) [catalysed by Pt /Pd] ½

(Accept any equation showing the oxidation of an alkane with 6 to 10 carbons.)

4 marks

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7. (b) Sucrose is a disaccharide found in sugar cane. Upon treatment with dilute mineral acids, sucrose gives two

monosaccharides, both of which have the formula C6H12O6.

sucrose

OCH2OH

HO

CH2OHOH

O

CH2OH

OH

OH

OH

O

(i) Name the two monosaccharides and give a ring structure for each.

*(ii) Name the linkage between the two monosaccharide units in sucrose.

(3 marks)

Mark Scheme .............................................................................................................................................. ��

7. (b) (i) 2×1

(ii) glycosidic linkage 1

3 marks

1999-AL-CHEM 1

6. (b) (i) Briefly explain why car exhaust contains carbon monoxide and nitrogen oxides.

(ii) The installation of catalytic converters onto car exhaust systems can reduce the concentrations of

pollutants in car exhaust. With the help of equations, briefly describe the function of a catalytic

converter.

(iii) Explain why leaded petrol is not used in cars equipped with catalytic converters.

(iv) Ozone is a pollutant derived from nitrogen dioxide. With the help of equations, account for the

formation of ozone from nitrogen dioxide.

(8 marks)


5

� Marking Scheme � 1999-AL-CHEM 1 � Mark

6. (b) (i) (I) CO: incomplete combustion of petrol 1

(II) NO: combination of N2 and O2 at high temperature ½

N2(g) + O2(g) → 2NO(g) (½)

NO2: air oxidation of NO ½

2NO + O2 → 2NO2

(ii) In the catalytic converter, Rh catalyses the reaction ½

2NO + 2CO → N2 + 2CO2 ½

Air is introduced to the converter and acts as an oxidizing agent. Pt/Pd catalyses the reactions: ½,½

2CO + O2 → 2CO2 ½

C7H16 + 11O2 → 7CO2 + 8H2O ½

(iii) lead/lead compounds can poison the catalysts Pt/Pd. 1

(iv) Upon absorption of UV radiation /sunlight, NO2 breaks down to give NO and O atom. ½

NO2

UV NO + O ½

O atom reacts with O2 in air to form O2. ½

O + O2 → O3 ½

8 marks

1999-AL-CHEM 2 6. (b) (i) Draw the structure, showing two repeating units, for each of the following polymeric materials:

(I) poly(chloroethene), and

(II) cellulose

(ii) Large quantities of poly(chloroethene) and cellulose are used in daily life. Suggest, with explanation,

an appropriate waste disposal method for each material.

(5 marks)

6. (d) In an experiment to determine the SO2 level in air, 200 dm3 of an air sample, measure at 298 K and 101 kPa

pressure, was bubbled into excess H2O2(aq) which converts the SO2 to SO42-

(aq). The resulting solution was

then treated with excess BaCl2(aq) to give 0.0583 g of BaSO4(s).

(i) Assuming that the air sample behaves ideally, calculate the concentration of SO2 in the sample,

expressing your answer

(I) in µg m-3

, and

*(II) in ppm by volume. (1 kPa = 1 × 103 N m

-2)

(ii) (I) Explain why power stations burning fossil fuels produce a considerable amount of SO2.

(II) Suggest TWO measures to reduce the emission of SO2 from such power stations.

(6 marks)

� Marking Scheme ��1999-AL-CHEM 2�� Mark

6. (b) (i) (I)

C C C C

Cl ClH

H HH

H

H

1

(II)

O

OH

OHO

HO O

OH

OHO

HO

β-glucose unit

β-glucose unit

1

(Award ½ marks for the glucose unit; ½ marks for the β-glycosidic linkage. Correct configuration at the C atoms are not required.)

high temp.


6

6. (b) (ii) (I) PVC:

Incineration and ½

treat flue gas in wet scrubber / with Na2CO3(aq) or an appropriate alkali. ½

Because incineration of PVC produces HCl which is an acidic gas. ½

Cellulose:

Incineration ½

Burning cellulose gives CO2 and H2O which are not air pollutants. 1

or, Land-filling (½)

Cellulose can be degraded by micro-organisms. (1)

5 marks

(d) (i) (I) SO2 ≡ BaSO4 (in terms of mole)

conc. of SO2 in air sample = 4)1632.06(137.3

0.0583

×++× 5 (for 1 m

3) = 1.249 × 10

-3 mol m

-3

= 80020 µµµµg m-3

(Also accept 80000 µg m-3

) 2

*(II) pV = nRT

partial pressure of SO2 = )V

n( RT = 1.249 × 10

-3 × 8.31 × 298 = 3.093 Pa

conc. of SO2 = 310 101

093.3

×× 10

6 = 30.6 ppm 2

(For (I) and (II), 1 mark for steps and 1 mark for answer.)

Treat this type of exercise as unit conversion or dimensional analysis, so you can do it as follows:

80020 µg m-3

i.e. 80020 × 10-6

g m-3

⇒ 80020 g SO2 in 106 m

3 air sample

Now what you need to do is to convert the unit ‘g’ to ‘m3’.

From pV = nRT = M

mRT,

V = 2-3

-1-1

1- m N 10101

K 298 K mol m N 31.8

mol g 64.06

g 80020

p

RT

M

m

×

×= = 30.6 m

3

∴ There are 30.6 m3 of SO2 in 106 m

3 air, i.e. the concentration of SO2 is 30.6 ppm.

NOTE: 1 atm = 1.01 × 105 Pa = 101 × 10

3 Pa = 101 kPa = 101 × 10

3 N m

-2

R = 8.31 J mol-1

K-1

= 8.31 N m mol-1

K-1

(= 0.08206 atm L mol-1

K-1

)

(ii) (I) Sulphur-containing compounds are present in fossil fuels, such as coal and oil. ½

These compounds give SO2 upon burning. ½

(II) Use low sulphur content coal /fuel ½

Install flue gas desulphurization system /wash flue gas with alkali. ½

6 marks

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7. (d) Fats and oils are triglycerides which undergo hydrolysis during digestion.

(i) Which compounds among N, P, Q, R and S below could be produced by the hydrolysis of a

triglyceride?

C17H35CH2OH

N

C17H35CO2H

P Q

H3NCH2CO2-+

C8H17CH=CH(CH2)7CO2H

R

CH2 CH CH2

OH OH OH

S

(ii) Draw a possible structure of a triglyceride which can give all the hydrolysed products that you have

chosen in (i).

(iii) (I) When oils are converted to hardened fats, what would happen to the structures of triglyceride

molecules?

(II) Such a hardening process can give a product with a longer shelf life. Explain.

(5 marks)


7


7. (d) (i) P, R and S 1½

(ii) 1

CH2O COC17H35

CHO

CH2O COC17H35

COC7H14CH=CHC8H17

(Accept correct structure of triglyceride derived from glycerin and fatty acid(s) chosen in (i).)

(iii) (I) The unsaturated carboxylic acid chains in triglyceride undergo catalytic hydrogenation ½

to give the corresponding saturated counterparts. ½

(II) Fats and oils having a high degree of unsaturation are more susceptible to oxidation / 1

oxidative rancidity which causes deterioration.

Hardening reduces the no. of unsaturated centers and therefore can increase the shelf life of

the substances. ½

2000-AL-CHEM 1

6. (c) CCl3F (Freon-11) is being replaced by CF3CH2F as a commonly-used refrigerant because CCl3F caused

depletion of the stratospheric ozone.

(i) With the help of equations, explain why CCl3F causes depletion of the stratospheric ozone.

(ii) Explain why CF3CH2F would not cause ozone depletion.

(4 marks)

� Marking Scheme � 2000-AL-CHEM 1 � Mark

6. (c) (i) In the stratosphere, CCl3F undergoes photodecomposition by absorption of UV radiation. ½

CCl3F UV

•CCl2F + Cl• ½

The Cl• radical initiate the following chain reactions: 1

Cl• + O3 → ClO• + O2 ½

ClO• + O3 → Cl• + 2O2 ½

∴ one Cl• can destroy a vast no. of ozone molecules.

(ii) C—F bonds are much stronger than C—Cl bonds ½

The UV radiation is not energetic enough to break the C—F bonds to give F• radicals. ½

4 marks

2000-AL-CHEM 2

5. (a) (i) State the two main air pollutants formed by burning sulphur-containing coal in power stations.

(ii) For each pollutant,

(I) state one of its environmental consequences, and

(II) suggest one measure to reduce its emission into the atmosphere.

(4 marks)

*(b) With the help of equations, outline the chemistry of smog formation from car exhaust.

(4 marks)


8


5. (a) Only the first two answers to be marked

(i) sulphur dioxide (compulsory answer) ½

+ suspended particulates /nitrogen oxides /hydrocarbons /carbon monoxide ½

(ii) (I) sulphur dioxide: acid rain/attack respiratory system ½

suspended particulates: attack respiratory system/ reduce visibility/smog ½

nitrogen oxides: acid rain/attack respiratory system/irritating (½)

hydrocarbons: carcinogenic /smog (½)

carbon monoxide: poisonous/toxic (½)

(II) sulphur dioxide: installation of scrubber/ desulphurisation system 1

particulates: bag filtration/electrostatic precipitator 1

nitrogen oxides: installation of scrubber/low nitrogen oxide burner/catalytic converter (1)

hydrocarbons: catalytic converter (1)

carbon monoxide: catalytic converter (1)

4 marks

5. (b) Car exhaust contains NO2 which, upon absorption of UV radiation (from sunlight), undergoes

photodecomposition: ½,½

NO2 UV

NO + O ½

The O atom reacts with other components of car exhaust (e.g. unburnt hydrocarbons) and those of the

atmosphere to give a variety of lachrymatory and toxic chemicals / PAN ½

O + O2 → O3 1

O + HCs → aldehydes / acids ½

or, O3 HCs → aldehydes / acids (½)

HCs + O2 + NO2 → PAN / lachrymatory substances ½

(Accept HCs with 5 to 12 carbons.)

4 marks

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6. (a) Sodium stearate CH3(CH2)16CO2-Na

+ , the most common soap, can be made by heating a triglyceride with

sodium hydroxide solution.

(i) Draw the structure of the triglyceride.

(ii) With the help of equation(s), describe the chemistry when soap is added to hard water.

(iii) Explain why washing soda, Na2CO3 ⋅ 10H2O, can help to reduce the hardness of water.

(4 marks)

(b) Product J, from the transformation below, is a commonly-used household detergent.

(i) Draw the structure of J.

(ii) State one advantage of using J as a detergent.

(iii) State one environmental problem associated with the use of J.

(3 marks)

(c) Dodecyl glucoside is a new detergent.

(i) Explain why dodecyl glucoside can be used in the cleansing of oily dirts.

(ii) Suggest how dodecyl glucoside can be degraded in the environment.

(4 marks)


9


6. (a) (i) CH2OCO(CH2)mCH3

CHOCO(CH2)nCH3

CH2OCO(CH2)pCH3

1

(m, n, p = 12-24, even number and one of them must be 16.)

(ii) Hard water contains Ca2+

/Mg2+

ions. ½

These ions react with stearate ions to form scum/precipitate. ½

2CH3(CH2)16COO- + Ca

2+ → [CH3(CH2)16COO]2Ca(s) 1

or, 2CH3(CH2)16COO- + Mg

2+ → [CH3(CH2)16COO]2Mg(s) (1)

(iii) carbonate reacts with Ca2+

/Mg2+

to form MgCO3(s)/CaCO3(s) and reduces the hardness of water. 1

4 marks

(b) (i)

CH3(CH2)11 SO3- Na

+

1

(ii) does not form precipitate /scum with hard water 1

or, does not work well in acid medium (1)

(iii) not readily biodegraded in the environment 1

3 marks

(c) (i) The long hydrocarbon carbon (tail) is hydrophobic/non-polar and can dissolve oily residue 1

(due to ‘like dissolves like’)

The glucose/sugar part is hydrophilic /polar /water soluble /can form H-bond with water 1

and can bring the oily residue into aqueous solution /cause the formation of water soluble micelles

(ii) hydrolysis of the glycosidic/glucosidic/sugar linkage ½,½

by enzymes/acids/bacteria/micro-organisms 1

4 marks

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7. (b) Aspartame, a sweetener, has the structure below:

(i) Name all functional groups in aspartame.

(ii) Upon hydrolysis, aspartame gives two amino acids. Draw their structures.

*(iii) Two electrodes are dipped into an aqueous solution containing the two amino acids in a pH 12 buffer,

and are connected to the two poles of a battery. Which species derived from these amino acids will

move faster towards the anode? Explain your answer.

(7 marks)


7. (b) (i) amine/amino ½

carboxylic acid/carboxyl/alkanoic acid ½

amide/peptide (link) ½

ester/alkyl alkanoate (max. 4 guessing, phenyl group not counted as a guess) ½

(ii)

COOH

COOHH2N COOHH2N (accept structures in form of Zwitterion.) 1+1

(iii) At pH 12, the amino acids exist as anions:

COO-

COO-

H2N COO-

H2N 1+1

(I) (II)

(I) is doubly (more highly) charged, and will moves faster towards the anode. ½,½

7 marks


10

2001-AL-CHEM 2

6. (a) The table below lists some information about five compounds, two of which are chlorofluorocarbons (CFCs) :

Name Structure Flammability Lifetime/years

CFC-11 CCl3F No 75

CFC-12 CCl2F2 No 108

HCFC-22 CHClF2 No 22

HCFC-123 CHCl2CF3 No 2

HFC-152 CH3CHF2 Yes 2

(i) Give two uses of CFCs in daily life.

(ii) Explain why the use of CFCs poses a problem to our environment.

(iii) Hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) are possible replacements for

CFCs. Which compound in the above table is the best choice? Explain your answer.

(7 marks)


6. (a) (i) Any TWO of the following: 1

� refrigerant

� aerosol propellant

� solvent to clean microchips and electronic parts

� blowing agent in foam plastics manufacture

� fire extinguishing material

(½ marks each)

(ii) CFCs are chemically unreactive compounds / have long life time and will not undergo reaction in

the lower atmosphere. 1

In the stratosphere, CFC molecules, upon absorption of UV radiation from sun, undergoes

homolytic cleavage to give Cl• free radical 1

Cl• free radicals react with ozone in the stratosphere:

Cl• + O3 → ClO• + O2 ½

ClO• + O3 → Cl• + 2O2 / ClO• + O → Cl• + O2 ½

The reaction is a chain reaction / Cl• is regenerated in the reaction (½)

∴one Cl• radical can destroy a large no. of ozone molecules (½) 1

(iii) HCFC-123 1

because it has a short life time and is not flammable ½,½

or, HFC-152 (1)

because it has no Cl (½) and has a short life time (½) (1)

� -------------------------------------------------- Take a break ----------------------------------------------------- ��

7. (c) Compound W is an artificial sweetener and has the structure shown below.

(i) Identify four functional groups in W.

(ii) Upon treatment with dilute mineral acids, W gives two monosaccharides. Draw a ring structure for

each monosaccharide.

(iii) Suggest two reasons for using artificial sweeteners as substitutes for sugar.

(6 marks)


11


7. (c) (i) Any FOUR of the following: 4 × ½

- phenol

- carbonyl / ketone

- ether / alkoxy

- alcohol / hydroxyl

- acetal

(ii) 2

(Accept ring structures in α or β forms)

(iii) Any TWO of the following 1+1

- diabetics cannot tolerate sugar

- noncaloric sweeteners facilitate weight loss

- artificial sweeteners do not promote tooth decay

- artificial sweeteners are hundred / thousand times sweeter than sugar

2002-AL-CHEM 1

6. (b) Under suitable conditions, sucrose undergoes hydrolysis to give glucose and fructose.

O

OHOOH

O

OHCH2OH

CH2OH

CH2OH

OH OHsucrose

(i) Draw a ring structure for glucose and one for fructose.

*(ii) When treated with Fehling’s reagent, sucrose and glucose demonstrate different behaviour.

(I) What are the major chemical components of Fehling’s reagent?

(II) Explain why sucrose and glucose demonstrate different behaviour when treated with Fehling’s

reagent.

(5 marks)


6. (b) (i)

(ii) (I) CuSO4(aq), NaOH(aq) and sodium potassium tartrate 1

(II) In aqueous solutions, the cyclic and non-cyclic forms of glucose are in equilibrium. ½

The –CHO group in the non-cyclic forms can reduce Cu2+ in Fehling’s reagent to Cu2O(s). ½

The rings in sucrose are locked (by the acetal function). ½

∴ Sucrose is non-reducing. ½

[5]


12

2002-AL-CHEM 2 6. (c) Both compounds K and L are natural fats that exist in human body.

(i) Draw structures of all products formed from the complete hydrolysis of K.

(ii) Suggest, with explanation, whether infra-red spectroscopy can be used to differentiate the products

formed from the complete hydrolysis of K.

(iii) Which compound, K or L, has the greater iodine value? Explain.

(6 marks)


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7. (a) Catalytic converters incorporated in car exhaust systems can reduce the emission of air pollutants into the

atmosphere. The catalysts commonly used are platinum (Pt) and rhodium (Rh).

(i) With the help of equations, briefly describe the reactions inside a catalytic converter.

(ii) The table below lists the relative levels of Pt and Rh in uncontaminated underground ice samples, and

in surface snow samples collected from 1973 to 1976 in central Greenland.

Relative level Samples

Pt Rh

uncontaminated underground ice samples 1 0.04

surface snow samples collected during 1973 6 1.5

surface snow samples collected during 1974 5 1.8

surface snow samples collected during 1975 40 5

surface snow samples collected during 1976 45 7

Source: Chemistry in Britain, April 2001

(I) Suggest a possible kind of human activity that was responsible for the medium-high levels of

Pt and Rh in snow in central Greenland prior to 1975.

(II) Suggest why there was a sudden increase in levels of Pt and Rh in snow in central Greenland

after 1975.

(iii) Suggest one measure that can help reduce the levels of Pt and Rh contamination.

(8 marks)


13


7. (a) (i) The catalysts catalyse the reduction of NO :

2 NO(g) + 2 CO(g) → N2(g) + 2 CO2(g)

and the oxidation of CO and of unburnt hydrocarbons (by air which is injected into the converter):

2 CO(g) + O2(g) → 2 CO2(g)

C7H16(g) + 11O2(g) → 7CO2(g) + 8H2O(g)

(Accept equations for the oxidation of alkanes with carbon no. from C5 to C9.

½

1

½

1

1

(ii) (I) mining / chemical industry 1

(II) The use of catalytic converters in cars was introduced in 1975 (in mid 1970s).

Particles containing Pt and Rh may be emitted from the catalytic converters.

1

1

(iii) Use electric car / Use other catalysts in the converter (Accept other reasonable answers.) 1

[8]

2003-AL-CHEM 2

5. (c) (i) Hardening of vegetable oils can be done by hydrogenation. Explain.

(ii) Which substance, vegetable oil or margarine, will turn rancid more readily? Explain.

(iii) The fumes from the two processes below were collected and analysed using infra-red (IR) spectroscopy.

The table below lists the wavenumbers of the major absorption peaks.

Process Wavenumbers of major IR absorption peaks / cm-1

Heating molten margarine 2950 and 1750

Frying potatoes with margarine 3100 (broad peak), 2959 and 1740

With the help of equation(s), suggest why the fumes from the two processes resulted in different IR

absorptions.

(7 marks)

Mark Scheme .............................................................................................................................................. ��


14

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6. (a) *(i) Inside level-one air quality office buildings, the concentration of carbon dioxide should not exceed

800 ppm. Express this concentration in µg m-3

units at 298 K and 1.01 × 105 N m

-2 pressure.

(You may assume that air behaves as an ideal gas.)

(ii) Ozone is commonly found in office buildings.

(I) Suggest a source of ozone in office buildings and write equations for its formation.

(II) A certain level of ozone in office buildings is beneficial to the indoor environment. Explain.

(iii) Methanal is one of the volatile organic compounds found in office buildings. Suggest a source of the

methanal.

(7 marks)

Mark Scheme .............................................................................................................................................. ��

6. (a) (i) pV = nRT =

rM

mRT

1

Concentration of CO2 =

V

m =

RT

rpM

= 6

65

1029831.8

108001001.1×

×

××× −

µg m-3

= 1.44 × 106 µg m

-3

1

1

(ii) (I) Ozone is formed in photocopying machines and in laser printers by the electric

discharge of oxygen.

1

O2 → O + O

O + O2 → O3

1

(II) Ozone can help kill bacteria in the office environment. 1

(iii) Polymers used in insulation foam and furniture stuffing are commonly made from methanal. 1

[7]

2004-AL-CHEM 1 5. (c) What is the main chemical ingredient of rubbing alcohol for disinfection ? Write an equation to show the

industrial synthesis of this chemical.

(2 marks)

Mark Scheme .............................................................................................................................................. ��

5. (c) propan-2-ol / 2-propanol / isopropanol 1

CH3CH CH2 + H2O CH3CHCH3

OH

catalyst

( H+ )

1

[2]

2004-AL-CHEM 2 5. (a) The active ingredient of household bleach is sodium chlorate(I), which is manufactured from chlorine.

(i) With the help of a chemical equation, suggest how sodium chlorate(I) can be obtained from chlorine.

(ii) Household bleach diluted by a volume ratio of 1:99 is widely used as an effective and inexpensive

disinfectant during the recent SARS epidemic outbreak.

A certain brand of household bleach contains 6.0 g of sodium chlorate(I) per 100 cm3 of the bleach.

Calculate the concentration of sodium chlorate(I), in mol dm-3

, in the diluted bleach.

(iii) With the help of chemical equation(s), suggest why household should not be used together with

(I) toilet cleaner which contains sodium hydrogensulphate(VI),

*(II) nail vanish remover which contains propanone.

(8 marks)


15

Mark Scheme .............................................................................................................................................. ��

� -------------------------------------------------- Take a break ----------------------------------------------------- ��

6. (a) The exhaust of heavy-duty diesel engines contains a significant amount of particulate matter (PM) and harmful

gases such as nitrogen oxides. A Continuously Regenerating Trap (CRT) is a device which is designed for

use in exhaust systems of buses and lorries running on diesel with low sulphur content to remove PM and some

of the harmful gases.

The diagram below shows how a CRT works:

(i) (I) With the help of chemical equations, explain why NOx are present in the engine exhaust.

(II) State one harmful effect of nitrogen oxides on the environment.

(ii) Carbon monoxide and hydrocarbons are two other harmful gases present in the engine exhaust.

Use chemical equations to show how these two gases can be removed in the catalytic chamber of a

CRT.

(iii) A CRT is an automated, self-regenerating device which does not require cleaning of the filter. In a

CRT, PM is trapped onto the filter and is then oxidised by one of the harmful gases to less harmful

products.

(I) Which elements is most abundant in PM?

(II) With the help of chemical equation(s), describe how PM trapped on the filter of a CRT can be

removed. Hence, explain why the filter need not be cleaned.

(iv) Suggest why buses and lorries equipped with CRT should not run on diesel with high sulphur content.

(9 marks)

Mark Scheme .............................................................................................................................................. ��

6. (a) (i) (I) At high temperatures, N2(g) reacts with O2(g) to give NO(g).

N2(g) + O2(g) → 2 NO(g)

2 NO(g) + O2(g) → 2 NO2(g)

1

½

½

(II) acid rain / photochemical smog 1


16

6. (a) (ii) 2 CO(g) + O2(g) → 2 CO2(g)

or, 2 CO(g) + 2 NO(g) → 2 CO2(g) + N2(g)

1

(1)

CnH2n+2(g) +

2

13 +nO2(g) → nCO2(g) + (n+1)H2O(g) (n is an integer) 1

(iii) (I) Carbon 1

(II) Nitrogen dioxide oxidises C in PM to CO2(g) / gaseous products 1

2NO2(g) + C(s) → CO2(g) + 2 NO(g)

C(s) + 2 NO(g) → CO2(g) + N2(g)

1

(iv) SO2 (or other sulphur compound) would poison the catalyst. 1

[9]

� -------------------------------------------------- Take a break ----------------------------------------------------- ��

7. (c) You are provided with four unlabelled bottles each containing one of the following white solids:

starch, sucrose, lactose and methyl α-2,3,4,6-O-mthyl-D-glucoside

Suggest how you would carry out tests to distinguish the four substances from one another.

Hint: The structures of sucrose, lactose and methyl α-2,3,4,6-O-mthyl-D-glucoside are shown below:

(6 marks)

Mark Scheme .............................................................................................................................................. ��

7.


17

2005-AL-CHEM 2 5. (b) Aspartame is a commonly used artificial sweetener.

(i) Copy the structure of aspartame into your answer book, and mark each chiral carbon atom with an

asterisk.

(ii) With reference to its structure, explain why aspartame is unstable in cooking.

(iii) In a coffee shop, a packet of sweetener contains about 5% of aspartame and 95% of silicon dioxide.

Suggest a reason for including silicon dioxide in the packet.

(4 marks)

Mark Scheme .............................................................................................................................................. ��

5. (b) (i)

1

(ii) Aspartame contains peptide links / ester groups.

They can undergo hydrolysis.

The high temperatures of cooking process can speed up the hydrolysis.

1

1

(iii) SiO2 acts as a filler / increases the bulk mass of the sweetener. 1

[4]

6. (a) Formaldehyde (methanal) is one of the commonly found organic indoor air pollutants.

(i) Suggest a source of household formaldehyde.

(ii) The indoor air quality (IAQ) standard for formaldehyde has been set at 0.10 ppm by volume.

Calculate the maximum allowable quantity of formaldehyde, in gram, in a room of volume 200 m3 at

298 K and 1.01 × 105 N m

-2.

(You may assume that formaldehyde behaves as an ideal gas.)

(iii) Some indoor air purifiers remove formaldehyde by chemical means. Suggest one chemical for the

removal of formaldehyde with the formation of less harmful products.

(iv) Name one other organic indoor air pollutant and suggest its source.

(7 marks)

Mark Scheme .............................................................................................................................................. ��

6. (a) (i) foam for insulation/ furniture stuffing/carpet/plywood 1

(ii) pV = nRT =

rM

mRT

m = RT

rpVM =

29831.8

30200101.01001.1 65

×

××××× −

= 24.5 mg

1

1

1

(iii) KMnO4 on Al2O3

HCHO is oxidised to less harmful and less volatile product (HCO2H).

1

(iv) pollutant source

benzene/toluene/ethylbenzene/xylene paint/paint strippers/thinners/gasoline

chlorinated hydrocarbons garments after dry cleaning

chloroform chlorine-treated water

2

[7]


18

2006-AL-CHEM 1 6. (b) The graph below shows a 24-hour variation of ozone concentration in the atmosphere of a city with heavy traffic:

With reference to the above graph, explain how ozone is formed and account for its overall concentration variation.

(4 marks)

Mark Scheme .............................................................................................................................................. ��

6. (b) The formation of ozone in the atmosphere involves the reactions:

NO2 NO + O 1

O + O2 → O3 1

In a city, the NOx are mainly derived from car exhaust. After 8 am, the traffic becomes heavy.

NOx accumulates in the atmosphere.

The formation of O requires UV radiation, NOx and hydrocarbons.

From 8 a.m. to 12 noon, there is a high intensity of sunshine. Concentration of O3 builds up in the

atmosphere. When the sun sets in the evening, the O3 concentration decreases.

1

1

[4]

2006-AL-CHEM 2 7. (c) (i) Cooking oils are unsaturated triglycerides. They are susceptible to oxidative rancidity, which involves

the formation of peroxide.

Draw the structure of a cooking oil, and write an equation to show the formation of peroxide.

(ii) The extent of oxidation of an oil can be determined by iodometric analysis.

In a typical experiment, 4.85 g of a sample of oil is treated with excess KI(aq) and H2SO4(aq). The

iodine liberated requires 21.20 cm3 of 0.012 mol dm

-3 Na2S2O3(aq) for complete reaction.

Given that when treated with acidified KI(aq), 1 mol of peroxide liberates 1 mol of I2, calculate the

number of moles of O2 absorbed per kg of the oil.

(5 marks)

Mark Scheme .............................................................................................................................................. ��

7. (c) (i) (The fatty acid in the structure should have an even number of C atoms and contain at least one C=C bond.)

CH2O

CHO

CH2O COR'

COR

CO(CH2)7CH=CH(CH2)7CH3

1

H

...... + O O

OHO ...

...

1

(ii) RO—OH + 2I- + 2H

+ → ROH + H2O + I2

I2 + 2 S2O32-

→ 2I- + S4O6

2-

O2 ≡ 2 S2O32-

No. of moles of S2O32-

used = 0.012 × 21.2 × 10-3

= 2.54 × 10-4

mol 1

No. of moles of O2 absorbed per kg of oil

= ½(2.54 × 10-4

) mol ÷ (4.85 × 10-3

kg)

= 26.2 × 10-2

1

1

UV

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