NSW IT{DEPENDENTTRIAL EXAMS _2009
CHEMISTRY TRIAL HSC EXAMINATION
MARIflNG GUIDELINES
Sectionl-PartA
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3
A
C
D
4
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f,
B
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D
C
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9
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B
10
C
tl
D
t2
D
13
C
l5
B
L4
A
Sectionl-PartB
a
Criteria
Ethylene is obtained by the cataly'ticcracking of longer chainedfractions of petroleum.
These hydrocarbonsare heatedstrongly in the absenceofair but in the presenceofa
catalyst. The carbon chains are broken into shorter chain lengths.Continued cracking
ultimatelv results in the formation of ethvlene.
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CHz: CHz + HzO ----------------CH:CHzOH
2
Thecatalvstusedis dilutesulfuricacid.
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Ethanol can be dehydratedto form ethylene.
CHTCHzOH
------>
CHz:
CHz +
HzO
This reaction can be performed in the presenceof a strong dehydratingagent such as
concentratedsulfuric acid.
Ethanol can be obtainedby the fermentation of sugarsfrom renewablesourcessuch as
sugar cane.
2 CH3CH2OH + 2COz
The use of non-renewablepetroleum resourcescan be reducedby obtaining ethylene via
the dehvdration of ethanol formed by fermentation using renewableresourcesof sugars.
CoHrzOo
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Criteria
Alkenes contain a reactive double bond in their carbon chain and so readily react with
bromine in aqueoussolution. The double bond opensup allowing bromine atoms to
bond with the carbon atoms in an addition reaction.
eg
CHz:CH2
+ Brz(uq)
CHzBTCI{zBr
Alkanes have only single bonds between carbon atoms. Hence, in the absenceof IfV
light, bromine in aqueoussolution doesnot react with alkanes.
Bromine water is a yellow/brown colour due to the presenceof the Br2 molecules. When
the Brz reacts with alkenes,the bromine water loses its colour. This allows the factthat a
reaction has occurred to be easily identifred.
In the presenceof alkanes,bromine water retains its yellow/brown colour as there is no
reaction.
Bromine water is therefore most suitable for the purpose of distinguishing between
alkanes and alkenes as it readily undergoesan easily identified reaction with alkenes but
does not react with alkanes.
NSW Independent Triql Exams 2009 - Chemistry Trial HSC Examination: Marking Criteia
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8(a
Criteria
Atoms of zinc are ionised and acceleratedto very high speedsin a particle accelerator
before smashinginto a lead target.If the zinc nuclei have sufficient energyto overcome
repulsive forces, they combine with lead nuclei forming a superheavyelementsuch as
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tt2.
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2
This type of researchincreasesour understandingof the structure of the atomic nucleus
and may produce new isotopesfor use in areassuch as industry and medicine.
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Criteria
3
The chemical reactions that take place in a battery involve electron transfer between
oxidant and reductant species.Thesereactionscan be consideredas separateoxidation
(electron loss) and reduction (electron gain) reactions. Electrons from the reductantare
transferredto the oxidant during the reactions.
ln the construction of a battery, thesetwo processesare physically separatedso that the
electrons must move through an externalcircuit for the transfer to take place, allowing
usable electrical energy to be generated. In the battery, the oxidant and reductant are
separatedby a barrier that allows ions to move through it to complete the electrical
circuit and thus keep the two sidesof the battery electrically neutral. The reductant
forms the anode or nesativeterminal of the battery. while the oxidant forms the cathode
or positive terminal.
a
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Criteria
COzret+ 2OH' )
COr'- + HzO (or molecularform with 2NaOFf)
Caz* +COzz )
)
CaCogr.)
Criteria
Molemassof CaCO: : 40 + 12+ 48: 100g .'.1000kg: 10,000moles
Molesof COz needed: 10,000moles
.'.Volumeof COz needed:10,000x24.79:247,900L
Volumeof air to passthrough"tred' : 247,900/ 0.00038: 6.52x 108L
20(c)
Criteria
1000kg CaCO:: 10,000moles
.'.I 80 kJ mol-l x 10,000moles: 1.8 x 106kJ energyrequired
1.8x 106kJ / 1 000 kJ mol-r: 1.8x 103mol naturalgas
.'.V: 1.8x 103mol It24-79 L mol-r: 4.46x 104L naturalgasneeded
21(a
Criteria
In the reactionmagnesiumatomsareoxidisedto form magnesiumions,showingthat it
reaction.
is an oxidation-reduction
Carbonatomsare reducedin thereaction(from +2 to 0).
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2I ( b
Criteria
The monomeric tetrafluoroethyleneis a low boiling substance(non-polar and low
molecular mass)and chemically reactive owing to its double C=C bond.
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The polymer is a plastic which is stableand unreactive,as it has no multiple bonds,
making it much more suitable for packins into a flare canister.
I
a
Criteria
Start Point (mI.)
0.0
18.6
12.8
End Point (mI.)
18.6
37.3
31.5
Mean Volume:
Vol HzSOa(mI.)
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18.6
18.7
18.7
18.7
2
Criteria
MolesNaOH= 2 x molesHzSOoor CuVu= 2xCuY^
25 x 0.220: 2 x 18.7x Cu and C": 0.147molL-l
Concentration
of HzSO
a: 0.147mol L-r
22(c
Criteria
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Initial Moles H2SO4 = 0.5 x 0.25: 0.125mol
Moles usedto dissolveMg: 0.125- molesremaining:0.125 - 0.0735= 0.0515mol
Molesof Mg: molesH2SO4:0.0515 mol Massof Mg:0.0515 x24.31:1.251965 s
(59.1%to 3 sf.)
.'. Percentage
of Mg by mass : 1.251965x 10012.12: 59.05o/o
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22(d)
Criteria
A25.0 mL pipetteis used.
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Criteria
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A measuredmass of flare mixture is reactedwith sulfuric acid under an inverted
measuring cylinder, initially filled with water. After equalising water levels the volume
of hydrogen gas collected is measuredand convertedto moles, using the molar volume
of a gas under collection conditions. As one mole of Mg produces one mole of
hydrogen, the mass of magnesiumcan be determined.
2
a
Criteria
CHTCH2OOCH (in expandedform showineall bonds).
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23
Criteria
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o
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Small quantities (approximately equimolar) of ethanol and formic acid are mixed
together in a boiling flask
A little concentratedsulfuric acid is added.
The flask is connectedvertically to a condenser.
The mixture is boiled under reflux.
.,
NSW Independent Trial Exams 2009 - Chemistry Trial HSC Examination: Marking Criteria - Page 3
23(c)
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I
Criteria
The isomericcompound is propanoicacid. (formula C3H6O2).
Propanoicacid will changethe colour of an acid-baseindicator,suchas litmus. Ethyl
formate has no acid-baseproperties. (or any other weak acid property such as
effervescenceof COz with a carbonate)
24(a)
Criteria
Phosphorusis^presentas phosphateion, and iron (III) ion forms a precipitateof iron(Il!
phosphate.Fe" + PO4'- ) FePOal.;.
It is important to remove the phosphateion from the effluent to minimise fertilising
action, which would promote growth of aquatic
and eutrophication.
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24(b)
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Criteria
n.
The purpose is to destroy bacteriaby strong oxidation (or LIV exposure)to ensureno
harmful Dathosenicbacteria are presentin the effluent.
Criteria
Add excessdilute silver nitrate solution to a 100 mL sample of the effluent. Separatethe
silver chloride precipitate by filtration, dry and weigh the solid.
Ag* + Cf )
AgCl le
The mass and concentration of chloride ion can be calculated from the formula AsCl.
I
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1
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1
Criteria
Na' Concentration(mg L-')
+:
: x: standards.
ver. * : downriver
[Na-]/ppm
NSWIndependentTrial Exams2009- ChemistryTrial HSCExamination:Marking Criteria - Page4
25(c)
Criteria
These downriver sodium concentrationsare within safe limits for freshwater organisms.
During low rainfall periods the river flow will decrease,reducing the dilution effect. As a
result the downriver sodium concentrationswill increase,possibly above the maximum
level.
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2
a
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Criteria
2
:o:
Q::Q
oxygen
molecule
The oxygen free radical is much less
stablethan the oxygen molecule
26( b
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Criteria
An oxygen free radical combines with an oxygen molecule by means of a coordinate
covalent bond.
.,
gr.---Coordinate
Bond
O
Section II
Question 27 - Industrial Chemistry
27(a
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Criteria
Sodium hydroxide is produced by the electrolysis ofbrine, a concentratedsolution of
sodium clrloride in water. The sodium chloride is obtainedby evaporation of seawater.
In the modern membrane electrolytic cell, the brine is electrolysedusing a titanium anode
and steel mesh cathode,supporting a membranewhich separatesthe electrolle into anode
and cathodecompartments.The membraneallows sodium ions to pass through to the
cathode,where water is reduced to hydrogen gas and hydroxide ions.
7
H2O+€)YrHz(s)+OHThe solution of sodium hydroxide is collected as it passesthrough the steel mesh cathode
and is then concentratedor obtained as the solid by evaporation.The anodereaction
produces chlorine by oxidation ofchloride ions.
Cf)YzC121ry+eSodium hydroxide is a white waxy solid which is extremely soluble in water. It is a very
strong base,and is the most widely used alkali in industry. Domestically it is used in drain
and oven cleaners,for its ability to dissolve fatty depositsby the saponification reaction.
Saponification is also the largest industrial use. It is used in the process of soap-making,
where sodium hydroxide is used to convert fats and oils to soapand glycerol. A soap is a
mixture of the sodium salts of fattv acids.
2
1
Criteria
For the reaction 2SOag1 + ort*l )
2SO31g1
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2
K" : tSOrl2+ ([SO2l2[O2l) : 6262- (2232x 114) : 0.069
NSW Independent Trial Exams 2009 - Chemistry Trial HSC Examination: Marking Criteria - Page 5
27
1l
Criteria
Propertv
Graph
(A,B,C,orD)
Total pressure
A
Kp
Yield of SOr
C
D
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At 25"C the reaction would be extremelv slow and it would take millions of years to reach
27(c
Criteria
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Three endothermicreactions are:
1. Decompositionof calciumcarbonate: CaCOn,y ) CaOi,y+ COztei
2. Ammonia recovery: Ca(OH), + 2NI{4CI ) 2NH3@ + CaClz + zHzO
3. Productionof sodiumcarbonate 2NaHCOv"r ) NarCOrrsr*COzror *HzOror
J
The most suitable fuel is natural gas which is easily transpoftedby pipeline, has a high
heat of combustionand bums cleanly, producing less carbon dioxide than other fossil
fuels such as coal.
a
L
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Criteria
Soap is a mixture of sodium salts of long chain fatty (carboxylic) acids. Each anionic
molecule consist of a long non-polar alkyl chain which is hydrophobic and a highly polar
and negatively chargedcarboxyl group which is strongly hydrophilic.
,/\,A.,n',a.,rr.,/\./\
2
/\/coo'
Mixed with water soapmolecules form clusters called micelles forming an emulsion.
Each micelle has a non-polar interior comprising alkyl groups and a surfacelayer of polar
hydroxyl groups which form hydrogen bonds with water molecules.Greaseand other nonpolar moleculesand are dissolved into the non-polar interior of the micelles, hencethe
cleansins effect of soap.
).
'2'/k
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A galvanic cell produces energy while an electrolytic cell consumesenergy. In a galvanic
cell an exothermic chemical reaction occurs to create a voltage and deliver current and
energy to an external circuit. e.g. electrodesof copper and magnesiumimmersed in a
potassium nitrate solution. The magnesium anode is oxidised to magnesium ions while
water is reducedto hydrogen at the copper cathode.
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An electrolytic cell can be made of stainlesssteel electrodesin a sodium chloride solution.
An external voltage source drives current through the cell. Water is reduced at the cathode
and the chloride ion is oxidised to chlorine at tle anode.
2
Question28 - Shipwrecks,Corrosionand Conservation
a
Criteria
provides
Steel-hulledshipsoperatein a stronglyoxidisingenvironmentin which seawater
a highly conductingelectrolytefor electrochemicalcorrosion. Oxygenin the atmospherg
and dissolvedin the surfacelayersof the ocean,is theprincipaloxidisingagent,andall
metalsarereducingagents. kon, the most widely usedmetal is a strongreductantin this
situation,initially undergoingoxidationto iron(Il) ions.
Fer"r ;
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P{+ +2€
Question 28(a) continues on the nextpage
NSWIndependentTrial Exams2009 - ChemistryTrial HSC Examination:Marking Criteria - Page6
Question2B(a) continued
The primary reduction reaction, which occurs on a suitablecathodic surface,is of oxygen
tohydroxideion. YzOz + HzO +2e ) 2OH-
The ultimate product is hydrated iron(III) oxide, or rust.
Measurestaken to combat corrosion include:
1) Preventing contact of the seawaterwith the steel using impervious coatings such as
grease,paint or a passivating metal.
2) Cathodic protection by embeddingslabs of a more reactive metal which becomesa
sacrificial anode. In this situation the steel becomesa cathodeand oxidation of iron is
prevented. Using an inert metal such as titanium, an external voltage can be applied
from the ship's generatorsto make the steel hull a cathodein the cell so created.
3) Use of passivating metals, such as aluminium alloys, in place of steel for fittings and
superstructurecan also reducethe problem of corrosion.
4) Taking care to prevent contact of seawaterwith less active metals or alloys, such as
copper andbronze, which act as cathodesand acceleratethe electrochemicalcorrosion
of steel.
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Together with salt spray the copper plate and galvanisedbracket createan electrochemical
cell in which the bracket is the anode.Corrosion of the bracket is accelerateddue to
contact with the copper, with both zinc and iron being oxidised to 2n ions, while oxygen is
reduced at the copper cathode. kon(Il) ions then react with oxygen to form a deposit of
rust.
a
3
Xu
Criteria
If suffrciently strong for the purpose a plastic bracket could be used, such as high density
PVC, which is unreactive. Otherwise a passivating metal such as stainlesssteel or titanium
could be used. Thesemetals develop a tough and impervious oxide layer, which
minimises or Dreventscorrosion under theseconditions.
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cxl
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Criteria
voltage source
2
steel
Stainless
anode
Horseshoe
Cathode
2E c
Sodium
rbonate
solution
l1
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2
Criteria
+ 2I{ +2€
Anode: 2OH- ) YzOzret+ H2O +2€ or IIrO ) YzOz<g)
+
+
6OH- or Fe3*+ 3e )
Cathode: e.g., Fe2Oys)+ 3H2O 6e ) 2Fqe
Fele
NSW Independent Trial Exams 2009 - Chemistry Trial HSC Examination: Marking Criteria - Page 7
When reduction of rust to iron is complete the cathodereactionbecomesthe reduction of
water producinqbubblesofhydrosen eas.
28(d
Criteria
Three iron nails were placed in a sodium chloride solution containing an indicator for the
presenceof iron(Il) ions (e.g., potassiumhexacyanofcrrate(Ill)). The first nail was
wrapped with a spiral strip of magnesiumribbon and the secondwith bare copper wire.
The third nail was left bare.
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Aft"era short time the indicator changedto blue around the secondand third nails showing
corrosion was occurring. Corrosion was much more rapid for the nail wrapped in copper
wire. Corrosion took place mostly at the ends of the bare nail where the metal had been
stressed. There was no observablecorrosion of the frst nail, however a white suspension
of magnesium hydroxide formed, showing that sacrificial protection was occurring. The
magnesium acted as an anodg with the iron becoming a cathodein the galvanic cell
formed.
e
Criteria
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Volta followed up Galvani's work with frog's legs and showedthat the electrical stimulus
came from a combination of two different metals (brassand iron) in contact with the
frog's leg. This led him to investigatedifferent electrochemicalcells. He invented the
voltaic pile, or battery to gain increasedvoltage. The pile consistedof discs of zinc and
silver or copper with cardboardseparatorssoakedin brine.
Faraday used Volta's batteriesto investigate electrolysis and the relationship between the
electric current of electrochemicalcells and the chemical reactionsat the electrodes. He
discovered the quantitative laws of electrolysis and introducedterminology such as anode,
cathode and electrolyte.
Question29 -The Biochemistryof Movement
a
Criteria
Marks
Provides a comprehensivedescription of the formation and importance of
glycogen.
Provides an accurateillustration of slvcosen and slucose.
Provides a description ofthe formation and importance of glycogen.
5-6
Provides an accurateillustration of slvcosen and slucose.
Provides a basic outline of the formation and importance of glycogen.
3-4
Provides a rudimentary illustration of glycogen and glucose.
Provides some relevant information.
t-2
Answer may include:
r Glycogen is a condensationpolymer formed from glucosethrough glycogenesis.
.
Initially glucose is converted to Glucose-6-phosphateby glucokinase or hexokinase.
Question 29(a) continueson the next page
NSW Independent Trial Exams 2009 - Chemistry Trial HSC Examination: Marking Criteria - Page 8