Assessment schedule
NZIC 2005
Chemistry 2.4 (AS90308)
While the writers of this assessment have worked to compile a resource that meets NCEA requirements, it has
no official status and teachers may wish to adjust questions and the assessment schedule as they see fit.
Question
One
Column
2
Evidence
(a)
H Cl
(b)
Cl Be Cl
(c)
Cl S Cl
(d) S C
(e)
Achievement
Merit
Three out of six
structures
correctly drawn.
All structures
correct.
Four shapes
correct.
All shapes
correct.
Four polarities
correct.
All polarities
correct.
Describes polar
bond.
Achieved plus
HCl explanation.
S
Cl P Cl
Cl
f)
One
Column
3
H
H C H
H
a) Linear
b) Linear
c) V-shaped
d) Linear
e) Trigonal pyramid
f) Tetrahedral
One
Column
4
Two
1
a) Polar
d) Non-polar
b) Non-polar
e) Polar
c) Polar
f) Non-polar
A bond in which one atom has a greater
attraction for the shared electron pair than
the other. With HCl, as the Cl is much
more electronegative / has a stronger pull
on electrons than the hydrogen, the Cl
atom has the greater attraction for the
electron pair leading to an uneven
distribution of charge and a polar bond.
Excellence
Question
Evidence
Achievement
Merit
2
NH3: The molecule has four regions of
negative charge around the central atom.
These are arranged tetrahedrally. Only
three are bonding regions which results in
the trigonal pyramid shape. If there are
only three regions of negative charge
around the central atom (all bonding) a
planar triangular shape results.
Explanation only
gives reason for
trigonal
pyramidal shape.
Achieved plus
requirements for
triangular shape.
3
H2O: has four regions of negative charge
around the central atom arranged
tetrahedrally. Only two are bonded,
therefore V-shaped.
CO2: has two regions of negative charge
around the central atom. It has no
unshared electron pairs and is therefore
linear.
Gives correct
shape for each.
Achieved plus
explains correct
shape of one
molecule.
Explanation of
correct shape for
both molecules.
4
PCl3: 3 polar bonds and unsymmetrical
arrangement of P–H bonds around central
atom so polarities do not cancel out
therefore polar. Water is a polar solvent
so PCl3 dissolves in water. ('like'
dissolves 'like'.)
CCl4: 4 polar bonds but symmetrical
arrangement of C–Cl bonds around
central atom so polarities cancel out
therefore non-polar. Non-polar molecules
do not dissolve in polar solvents, so CCl4
does not dissolve in water.
States correct
shape, polarity
and solubility of
each without
explanation.
Achieved plus
explanation of
shape, polarity
and solubility of
one molecule
or
partial
explanation of
both.
Complete
explanation of
shape, polarity
and solubility of
both molecules.
Type of solid
Na2O: ionic
SiO2: covalent network
SO3: molecular
ClO2: molecular
Three out of four
correct.
Type of particle
Na2O: ions
SiO2: atoms
SO3: molecules
ClO2: molecules
Three out of four
correct.
Name of bond
Na2O: ionic
SiO2: covalent
SO3:
(weak) intermolecular
ClO2: (weak) intermolecular
Three out of four
correct.
Three
1
For three out of
four rows
completely
correct give one
Merit.
(Question has 3
Achieved
possibilities plus
one Merit)
Excellence
Question
Evidence
Achievement
Three
2
MgO: high M.Pt.
MgO is an ionic solid and high melting
point is due to strong attraction
between ions.
P4O6: low M.Pt.
P4O6 is a molecular solid and its low
melting point is due to the weak
attraction between molecules.
Correctly
identifies both
melting points as
high or low.
Achieved plus
explanation of
one solid.
Full explanation
of melting points
of both solids.
Four
(a)
Gold is malleable because (layers of)
particles move across each other and the
electrons move with (or between) them.
Sodium chloride The ions are fixed in
place when solid, so solid NaCl cannot
conduct, but when molten the ions are
free to move in response to an electric
field and therefore conduct.
Iodine has only weak intermolecular
forces holding the atoms together and
these are easily broken so the solid
readily sublimes on heating.
One explanation.
Any two
adequate
explanations.
All three detailed
explanations.
Graphite is a two-dimensional giant
covalent structure in which three carbon
atoms are strongly bonded to three other
carbon atoms in a flat plate-like structure.
There are weak intermolecular forces
between the layers, allowing the layers
can move across each other and therefore
leave a mark when rubbed on paper.
Diamond is a three-dimensional covalent
network structure with each carbon atom
bonded by strong covalent bonds to four
other carbon atoms, making it so hard and
strong that it can cut glass.
Graphite or
diamond
structure
correctly
described.
One full
explanation.
or
two adequate
explanations that
do not mention
the bonding in
both structures.
Both fully
explained.
(b)
Merit
Excellence
Sufficiency Statement. These exams are not pre-tested. The statements below are a guide and schools should
feel free to adjust them to get a sensible distribution.
Achieved
A total of SEVEN opportunities answered correctly at Achieved or higher.
Merit
A total of EIGHT opportunities answered correctly with 5 at Merit and 3 at Achieved
Excellence
A total of NINE opportunities answered correctly with 3 at Excellence, 3 at Merit and 3 at Achieved.