NSW INDEPENDENT TRIAL EXAMS – 2006
CHEMISTRY (PRELIMINARY EXAM)
MARKING GUIDELINES
Section I
1
C
2
D
3
A
4
D
5
B
6
C
7
B
8
C
9
B
10
B
11
A
12
D
13
A
14
B
15
C
Section II
Question 16(a)
Criteria
S: 2, 8, 6.
Marks
1
Question 16(b)
Criteria
Sodium forms ionic bonds with sulfur, with sulfur gaining two electrons from each sodium
atom.
Na+
S
2,8
2, 8, 8
Na+
Chlorine forms covalent bonds with sulfur:
S Cl
Cl
Marks
1
OR
1
S – Cl
Cl
Question 16(c)
Criteria
Example: boiling point.
Marks
2
Na2S has a much higher BP than SCl2. The vaporisation of Na2S requires breaking strong ionic
bonds but vaporising SCl2 requires separation of molecules which are held together by much
weaker dipole-dipole attraction.
Question 17(a)
Criteria
For example: the fractional distillation of petroleum.
Marks
1
Petroleum is a mixture of hydrocarbons with different boiling points.
Question 17(b)
Criteria
Using fractional distillation of petroleum as the example: products include any TWO of:
Propane, butane, petrol, diesel, kerosene, all used as fuels.
Oils used as lubricants and boiler fuel.
Greases used as lubricants and boiler fuel.
Bitumen used in paving roads.
Marks
2
NSW Independent Trial Exams 2006 – Chemistry (Preliminary Examination): Marking Criteria - Page 1
Question 17(c)
Criteria
Using fractional distillation of petroleum as the example:
The process produces some waste gases which cause air pollution or must be burned
releasing CO2.
Petroleum contains varying amounts of sulfur which must be removed. If allowed to
burn, acidic and irritating sulfur dioxide is produced.
Question 18
Criteria
The production of hydrogen from water involves the breaking of strong O-H bonds, which
requires more energy than is released in forming H-H and O-O bonds.
H2O(l) + energy
Marks
2
Marks
3
H2(g) + ½O2(g)
Much less energy is required to separate water molecules from each other, when water is
vaporised. Less energy is needed to break the hydrogen bonds between molecules than the
covalent bonds within them.
Question 19(a)
Criteria
First ionisation energy is that energy needed to remove one electron from the neutral gaseous
atom expressed in kJ per mole of atoms e.g. Na(g)
Na+(g) + e-.
Marks
2
Question 19(b)
Criteria
The reactivity of a metal depends upon the ease with which its atoms lose electrons to form
ions.
Marks
1
Sodium has a low ionisation energy and therefore a strong tendency to form ions, making it
reactive.
1
Question 20(a)
Criteria
Example: aircraft frames replacing timber.
Marks
1
Question 20(b)
Criteria
Aluminium is a very reactive metal, producing very stable compounds.
Marks
1
A large amount of electrical energy is needed to extract aluminium and this was not available
earlier.
Question 20(c)
Criteria
As large amounts of energy are needed to extract aluminium from its ore it is much more
efficient, and benefits the environment to recycle discarded aluminium. Recycling only
requires melting which involves much less energy.
Question 21(a)
Criteria
Air: magnesium burns with an intense white flame, forming a white ash of magnesium oxide.
1
Marks
2
Marks
1
Water: magnesium reacts slowly with cold water but rapidly if heated, releasing bubbles of
hydrogen gas (optional: residue of magnesium hydroxide).
1
Acid: magnesium reacts vigorously, dissolving and releasing hydrogen gas.
1
NSW Independent Trial Exams 2006 – Chemistry (Preliminary Examination): Marking Criteria - Page 2
Question 21(b)
Criteria
Mg(s) + ½O2(g)
Mg(s) + 2H2O
Marks
1
MgO(s)
Mg(OH)2(s) + H2(g)
Mg(s) + 2H+
1
Mg2+ + H2(g)
1
Question 22(a)
Criteria
Examples: Ionic: sodium chloride
Macro: diamond
+ ion
- ion
Marks
3
C
C
C
C
C
Sodium chloride consists of a lattice of positive sodium ions and negative chloride ions held
together by electrostatic forces (ionic bonds).
Diamond consists of an endless array of carbon atoms, each of which are bound to four
neighbours by strong covalent bonds.
Question 22(b)
Criteria
Water is highly polar and strongly attracts both cations and anions separating them to form a
solution.
The attraction is not strong enough to break the covalent bonds in a macromolecule like
diamond.
Question 23(a)
Criteria
Water has:
A high boiling point for its molecular size, and is liquid.
A high heat capacity making it resistant to large temperature changes.
Solvent properties enabling life processes.
Question 23(b)
Criteria
The lake could be contaminated with chemicals of outside life forms.
Interfering with the lake could result in irreversible damage.
Life forms could be hazardous to us and/or others surface organisms.
Question 24(a)
Criteria
Iodine is completely non-polar. It dissolves in a non-polar solvent such as hexane, but not in
water which is highly polar. “Like dissolves like”.
Question 24(b)
Criteria
Example: sugar (glucose, sucrose, etc).
Marks
1
1
Marks
1
1
1
Marks
2
Marks
2
Marks
1
Question 24(c)(i)
Criteria
Filtration or decanting.
Marks
1
Question 24(c)(ii)
Criteria
Distillation
Marks
1
NSW Independent Trial Exams 2006 – Chemistry (Preliminary Examination): Marking Criteria - Page 3
Question 25
Criteria
After mixing:
Marks
Pb(NO3)2
+
2NaI
0.10
0.10
Initial:
-0.05
-0.10
Change:
0.05
0
Final:
-1
Final concentrations: (mol L )
[I-] = O [Pb2+] = 0.05 [Na+] = 0.1 [NO3-] = 0.15
PBI2(s)
0
(+0.05)
-
+
2NaNO3
0
+0.10
0.10
Question 26(a)
Criteria
Propane is combustible. The crushing or piercing of a container with residual propane could
result in an explosion.
Question 26(b)
Criteria
Propane burns cleanly releasing a large amount of heat. While it is a gas under normal
conditions it is easily compressed to a liquid for storage and transport, reverting to a gas when
the pressure is released.
1
1
Marks
1
Marks
2
Question 26(c)
Criteria
Propane must be stored in strong metal containers which are free of corrosion or flaws. The
containers must be kept in a cool place and secured to prevent mechanical damage.
Marks
3
Question 27(a)
Criteria
Mass of 10 squares = 0.12g
Marks
Moles of Mg =
0.124
= 0.0050mol
24
Moles of HCl needed = 0.01mol (2:1)
In 10mL of 2 mol L-1 HCl there are 0.02 moles, much more than required.
Question 27(b)
Criteria
Students graph shows that reaction time is (approximately) inversely proportional to acid
concentration.
Question 27(c)
Criteria
Mean temperature rise = (3.3 + 4.0 + 4.7 + 3.9 + 4.8 + 5.2) = 4.30C
Heat produced = mc∆t = 100 x 4.18 x 4.3 = 1800 J
1800
Heat per mole of Mg =
= 360 kJ
5 × 10 − 2
Question 27(d)
Criteria
Using a fume cupboard, safety goggles, lab coat. Take care when handling acid, gloves etc.
1
1
Marks
3
Marks
1
1
1
Marks
2
The Preliminary examination, marking guidelines/suggested answers and ‘mapping grid’
have been produced to help prepare students for the HSC to the best of our ability.
Individual teachers/schools may alter parts of this product to suit their own requirement.
NSW Independent Trial Exams 2006 – Chemistry (Preliminary Examination): Marking Criteria - Page 4