Final Mark Scheme
Question
2815t01
Expectedanswers
January2004
Marks Additional
guidance
(a)
(i)
(Enthalpychangeof) formation(of magnesiumoxide)
(1);
(Enthalpychangeof) atomisation(of magnesium)(1);
3
Allow (enthalpy
changeof)
(of
sublimation
magnesium)
Firstionisation
(of magnesium)
enthalpy
(1)
(b)
(ii)
Mg'.(g) and O2-(g)(1)
1
( iii)
Electronbeinggainedis repelledby the negativecharge
of the ion / aw (1)
1
(i)
Latticeenthalpy= -l 49 - 736- 1450- 248- 650- 602
(1);
= -3835(kJmot-l)(1)
2
Allow ecf from
one error (1)
( ii)
Latticeenthalpyof bariumoxide is less exothermicthan
that of magnesiumoxide/ latticeenthalpyis smallerin
magnitude/ ora (1);
Mg'* has a smallerionicradiusthan Ba2*| Mg'. has a
higherchargedensitythan Ba2*| ora(1);
3
Not biggeror
smallerlattice
enthalpy
Correctparticles
mustbe usede.g.
not Mg hasa
smallerradius
Allow so has
strongerionic
bonds
Not resistantto
heat
Statesymbols
not essential
Particlesused
must be correct
e.g.not Mg is
morepolarising
Allow marksvia a
diaqram
so strongerattractionbetweenthe positiveand negative
i o n( 1 )
(c)
(d)
Allow first
ionisation
energv
Statesymbols
essential
High meltingpoint/ (very)large latticeenthalpy/ aw (1)
BaO + CO2(1)
(i)
BaCOg)
(ii)
Decomposition
temperature
higherfor BaCOeI ora(1')
Polarising
abilityof cationdecreases
fromMgt*to Ba2*
(1);
Polarisation
causesdistortion
of the chargecloud
the
around carbonate
ion/ polarisation
weakensthe
covalentbondswithinthe carbonate
ion (1)
1
1
3
Total
= {5
2815t01
January2044
Expectedanswers
Marks Additional
guidance
Final Mark Scheme
Question
(1)
Oftenarecatalysts
1
(i)
ion (1);
lor a cleardrawingof a tetrahedral
Tetrahedral
(1)
Bondangleof 109.5t 0.5"
2
ii)
( iii)
cr-(1)
1
1
(a)
(b)
(iv)
acid/ (concentrated)
(Concentrated)
hydrochloric
solutionof an ionicchloride(1)
Suitableequation
+ 6H2O
e.g.[Cu(HrO)u]'.+ 4Cf ) [CuClaJ2Or
4HzO;
) [Cu(HzO)z(NHs)o]'**
[Cu(HzO)uJ'**4NH3
Reactionin whicha ligandis swappedor displacedby
anotherligand/ aw (1)
Allow
are
compounds
often
paramagnetic
Not metallic
properties
Allow square
planar(1)with
bondangleof 900
(1)
Tetrahedral
structuremust
haveat leastone
wedoe
Allow correct
formula
2
Not ligandis
substituted
Total
=f
Final Mark Scheme
Question
(c)
Expectedanswers
January2OO4
Marks
Additional
guidance
Allow one markif
all the oxidation
numbersfor
oxygen(and
hydrogen)
are
correct
lgnoreelectrons
for the first mark
- Oxidation
numberof oxygenchangesfrom
Oxidation
-1 to 0;
- oxidation
Reduction
numberof oxygenchangesfrom
-1 to -2 (1)
2
(i)
2 M n O a - + 6 H+* 5 H 2 O 2) 2 M n 2+*8 H z O + 5 O z
Correctreactants
andproducts(1);
(1)
Balancinq
2
( ii)
Mofesof MnO+-= 17.5x 10-' x 0.0200/ 3.5 x t0-4 (1);
Mofesof HzOz= 2.5 x molesof MnOc'|8.75 x 104 (1);
8'75x10-a =
Conc of HzOz0.0350(molOm-3)(t)
0.025
3
Allow ecf within
question
Allow 0.035
Not 0.04/ 0.03
/ potassium
Aqueoussodiumhydroxide
I
thiocyanate
(1);
thiocyanate
ammonium
Appropriate
observation
e.g.orange-red
/ brown/
ppt
/
foxy-red
with
NaOH(aq)
brown-red
or (blood)red
(1)
withKSCN
2
Allow hydroxide
(ions)or
(ions)
thiocyanate
(a)
(b)
2815t01
Total
=$
Final Mark Scheme
Question
4
January 2004
2815t01
Marks
Expectedanswers
Ghemical formula
Correctformulaof all chlorides(1);
Numberof outerelectronsper atom increases
oxidationnumberincreases(1);
14
Allow AlClsor
Al2c16
Structureand bonding
NaCl or MgCl2?ra ionicandAlClgor SiCla?r€covalent
(1)
NaCl or MgCl2aregiantandAlCl3or SiCl+aresimple
(1)
And any two from
diagramfor oneof the ionic
Correct'dot-and-cross'
(1);
chlorides
diagramfor oneof the covalent
Correct'dot-and-cross'
(1);
chlorides
showingthe dative
for AlzCl6
Correctstructure/bonding
bonding(1);
Drawingof NaCllattice(1);
Do not award
markif one
bondingor one
structureis wrong
Do not penalise
incorrectanswers
in thesetwo
marks
Action of water
Any four from
dissolvein water/ NaClor MgCl2dissolve
lonicchlorides
in water(1):
givea neutralsolution/ NaClgivesa
lonicchlorides
neutrafsolutionor pH 7 | MgCl2givesa slightlyacidic
solutionor pH 6-7 (1);
/ covalentchlorides
Covalentchloridesare hydrolysed
(1);
react/ SiCl4or AlClsreactor arehydrolysed
/ SiCl4or AlCls
giveacidicsolutions
Covalentchlorides
giveacidicsolutions
or pH lessthan6 (1)
Suitableequatione.g. SiCla + 2H2O )
(1)
Additional
quidance
Allow dissociate
in water
Allow polarisatio
of water
moleculesby Af.
to
As alternative
mark
hydrolysis
Allow other
speciessuchas
si(oH)4
SiO2 + 4HCI
Melting points
NaCl, MgClzor ionicchlorideshave electrostatic
attractionbetween ions / attractionbetweenpositiveand
negativeions (1);
AlClg,SiCl4or simplemolecularlatticehave van der
Waals force of attraction(1);
forces (1)
Strong ionic bonds and weak intermolecular
QWC - one mark for technicalterms
Award one mark if the candidatehas illustratedthe
answers correctlyusing at least three of the technical
ionic
terms (1) - hydrolysis,hydration,intermolecular,
covalent,lattice,electrostatic,van der Waals,
polarisation,dativebonding.
Not weak
covalent bonds
Total
=14