MARKING GUIDELINE
NATIONAL CERTIFICATE
CHEMISTRY N4
14 NOVEMBER 2012
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MARKING GUIDELINE
-2CHEMISTRY N4
T320(E)(N14)T
QUESTION 1
1.1
1.2
1.3
1.1.1
KBr √
(1)
1.1.2
NH3 √
(1)
1.1.3
NH3 √
(1)
1.1.4
KBr √
(1)
1.1.5
N2√
(1)
1.1.6
Cu √
(1)
1.1.7
NH3√
(1)
1.1.8
Cu √
(1)
1.1.9
KBr √
(1)
1.1.10
N2√
(1)
1.2.1
Delocalised electrons √
1.2.2
Delocalised elctrons √
1.2.3
Strong electrostatic forces √
1.2.4
Bonds are omnidirectional √
1.2.5
Closely packed positive ions √
(5)
1.3.1
One atom supplies both the electrons √ that is shared by the atoms
in the bond√
(2)
1.3.2
(3)
1.4
Covalent bond √
Share √ electrons √
Octet rule satisfied √
Orbitals overlap √
Molecule formed √
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(5)
[25]
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MARKING GUIDELINE
-3CHEMISTRY N4
T320(E)(N14)T
QUESTION 2
2.1
COMPOUNDS
Lewis structures
NH3
Does the
Yes √
molecule obey
the octet rule?
Number of
3√
bonding electrons
pairs
Number of lone
1√
electron pairs
Shape of the Trigonal pyramidal
molecule
√ or distorted
tetrahedron
2.2
2.3
2.4
BF3
CIF3
No√
No√
3√
3√
0√
2√
Trigonal
planar√
T-shaped√
distorted
trigonal
bipyrimidal
or
(15)
Smaller√
The positive nuclear charge is bigger. √
Electrons are attracted stronger and closer√
(3)
2.3.1
2.3.2
(2)
Stronger√
Weaker √
Two different structures with alternating single and double bonds are
possible√
Bondlength shows that Benzene exits in an intermediate hybrid structure √
Electrons are delocalised and all bonds in same length
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MARKING GUIDELINE
-4CHEMISTRY N4
T320(E)(N14)T
(5)
[25]
QUESTION 3
3.1
3.1.1
H2CO3 + H2O  HCO3-√ + H3O+√
(2)
3.1.2
Ka = [HCO3-][H3O+]√√
H2CO3
(2)
H2CO3 is a weak acid√ and ionises incompletely√
(2)
3.1.3
3.2
(2)
3.3
3.4
3.3.1
Proton donor√
(1)
3.3.2
Substance that accepts an electron pair√√
(2)
3.3.3
HC or H+ √
(1)
3.3.4
NH3 + H2O  NH4+ + OH-√√
NH3 forms OH- in water
(2)
3.4.1
(2)
3.4.2
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HCOC√
C has a higher electronegativity than Br√
The electrons are more displaced towards C√
Proton is more readily removed√
(4)
[20]
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MARKING GUIDELINE
-5CHEMISTRY N4
T320(E)(N14)T
QUESTION 4
4.1
4.2
4.3
4.4
4.1.1
Diamond and graphite are two distinct forms of carbon√
(1)
4.1.2
Lubricants, crucibles and ‘lead’ in pencils√√
(2)
4.1.3
No, it is an impure form of carbon (a mixture) √
(2)
4.2.1
Clear limewater√ turns milky√
(2)
4.2.2
Covalent√
(1)
4.2.3
NiO(s) + CO(g)  Ni(s) √ + CO2(g) √
(2)
Deuterium and Tritium√
Different numbers of neutrons√
(2)
2Na(s) + H2O(I)  2√NaOH(aq) √ + H2(g)
(3)
[15]
QUESTION 5
5.1
Ostwald process√
(1)
5.2
5.2.1
5.2.2
5.2.3
5.2.4
5.2.5
(5)
D√
B√
A√
B√
C√
5.3
4NH3 √+ 3O2  2N2√ + 6H2O Balanced√
5.4
5.4.1
D H2O2√
5.4.2
A SO3√
5.4.3
E CaO√
5.4.4
B AI2O3√
5.4.5
C NO√
(4)
(5)
[15]
TOTAL:
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