Assessment schedule
NZIC 2006
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.
Evidence
ONE
(a) (i)
(a) (ii)
Achievement
C CH2O
E CH2Cl2
C:
Carbon does not have eight electrons
associated with it.
H C H
O
E: The non bonding electrons on the
chlorine atoms are not shown
(b)
TWO
(a)
(b)
(c)
H
H C O H
H
(i).
Merit
Excellence
Only these two
structures
circled.
Cl
H C Cl
H
One
description of
error and its
associated
Lewis diagram
correct.
Both
descriptions and
Lewis diagrams
correct.
Correct
(ii)
N N
SO3, trigonal planar, O3 Bent, PH3, triangular pyramidal
and CH4 tetrahedral.
The shape of a molecule or ion is determined by:
 The number of regions of negative charge around
the central atom.
 The regions of negative charge will repel each other
as far as possible.
 The number of bonding and non-bonding regions.
SO3 and O3 have three regions of negative charge around
the central atom. These will be distributed to the corners
of a triangle.
All the regions are bonding in SO3. Therefore the shape is
planar triangular.
In O3 there are two bonding regions and one non-bonding
region so the molecule is angular/bent/V-shaped.
In NH3 and CH4 there are four regions of negative charge
around the central atom which will be distributed to the
corners of a tetrahedron.
In NH3 there are three bonding pairs and one nonbonding pair so the molecule is a trigonal pyramid shape
In CH4 all regions are bonding pairs so the molecule is
tetrahedral.
A polar bond is a covalent bond that has a negative end
and a positive end OR unequal sharing of electrons
Three correct
All correct.
Two of the
bullet points
mentioned.
Some attempt
to relate these
to the
examples.
Factors
determining
shape clearly
stated.
Two shapes
clearly explained
Correct.
Factors
determining
shape clearly
stated.
All shapes
clearly
explained
Evidence
Achievement
(d) (i)
CO2 and O2 non-polar, SO2 polar.
Correct.
(d) (ii)
Although the CO2 molecule contains polar bonds, the
CO2 molecule is symmetrical and so the polarities of
the bonds balance out/cancel and overall the molecule
is non-polar. The SO2 molecule also contains polar
bonds, and there are 3 areas of negative charge around
the central S atom (2 bonding pairs and 1 lone pair)
resulting in a non-symmetrical molecule that is polar.
The O2 molecule does not contain polar bonds, and is a
symmetrical molecule, so it cannot be a polar
molecule.
Describes one
factor
contributing to
polarity.
THREE
(a) (i)
(a) (ii)
(a) (iii)
(b)
1
Cu
2
I2
3
NaCl
4
SiO2
 Copper is a metal. Metals are solids with a high
melting point that conduct electricity because they
consist of an orderly array of positive ions held
together by a mobile sea of electrons. The
electrons move randomly through the lattice and
are shared by numerous positive ions, which
provide the strong chemical bonds holding the
metal together.
 The free moving electrons are the reason why the
solid conducts electricity, as the electrons are able
to move towards the positive pole when a voltage
is applied.
 Iodine is a covalent solid with a low melting point
that does not conduct electricity because it
consists of covalently bonded, non-polar
molecules which results in weak intermolecular
forces between the molecules.
 Covalently bonded molecules do not conduct
electricity because they do not contain any
charged particles.
Water is a polar solvent because it contains very
polar molecules. NaCl is an ionic compound,
consisting of positive and negative ions. Ionic
substances dissolve in polar substances.
Solid LiCl consists of ions fixed into a lattice There are
no free moving charged particles to carry the electric
current. Therefore, solid LiCl does not conduct. Once
the LiCl melts, the ions are free to move. Thus molten
LiCl is able to conduct a current. LiCl is also soluble
in water. When it dissolves, the ions are free to move,
and thus able to conduct a current.
Merit
Excellence
Limited
discussion e.g.
2/3 correct but
some details
missing.
All three
molecules
explained
correctly.
2 Points
covered.
3 Points covered.
Both melting
point and
electrical
conductivity
explained in
terms of
structure and
bonding for
both Cu and I2
Like dissolves
like.
Explains that
water is polar,
and NaCl is an
ionic substance,
and therefore
will dissolve in
water.
LiCl
 does not
conduct when
solid,
 but does
when molten
 or in solution.
All correct.
Describes LiCl
as consisting
of ions.
Full answer
with
discussion.
Sufficiency Statement. These assessments are not pre-tested. The statements below are a guide and schools
should feel free to adjust them to get a sensible distribution.
Achievement
Merit
Excellence
A total of SIX opportunities correct at Achievement or higher
A total of SEVEN opportunities correct with three at Merit or higher
A total of NINE opportunities correct with four at Merit or higher and two at Excellence