NZIC 2014 Assessment Schedule: 91164 (2.4)
Q
Evidence
ONE
(a)
C
Achievement with Merit
Achievement with
Excellence
THREE structures correct
Br Br
O
Achievement
O
H
H
C
F
F
H
(b)
O
Cl
The central atom of PH3, has four regions of
electron density/electron clouds around it. The
regions of electrons are arranged as far apart as
possible to minimise repulsion, making a tetrahedral
arrangement. Only three of these regions of
electrons are bonding so molecular shape is
trigonal pyramidal. This gives a bond angle of
~109°.
The central atom in BCl3 has three regions of
electron density around it, all of which are bonding.
The regions of electrons are arranged as far apart as
possible to minimise repulsion, making a
trigonal planar. This gives a bond angle of ~120°.
Shape of PH3 (trigonal
pyramidal) or BCl3 (trigonal
planar) correct.
Bond angle of either PH3
(~109o) or BCl3 (~120o) correct.
Both molecules are tetrahedral.
Polarity of CHCl3 (polar) or CH4
(non polar) correct.
C-Cl (or C-H) bond is polar with
reason.
The arrangement of electrons for
BOTH molecules is used to
explain the shape OR bond
angle
OR
The arrangement of electrons for
ONE molecule is used to
explain the shape AND bond
angle.
The arrangement of the regions
of electron density around the
central atom is used to explain
the shapes and angles of the
molecules.
CHCl3 is polar. CH4 is non-polar.
(c)
Both molecules are tetrahedral due to four regions of
negative charge around central C atom, all of which
are bonding.
In CHCl3, the C–H and C–Cl bonds are polar due
to difference in electronegativity of the atoms / the
bonding electrons are unevenly shared. However,
since Cl is more electronegative than H the polarity
of the C-Cl bond is different from that of C-H.
Hence when the bonds are arranged tetrahedrally
around the C atom the bond dipoles are unable to
cancel so the molecule is polar.
In CH4 all bonds are polar due to difference in
electronegativity of the atoms . S i nc e t h es e
polar bonds are all the same / arranged evenly
around the central C atom, the bond dipoles cancel.
Hence the molecule is non-polar.
The difference in
electronegativities between C
and Cl (or C and H) are used to
explain that C-Cl (or C-H)
bonds are polar.
OR
Links the spread of charge to the
overall molecule polarity.
The polarity of both molecules
are explained and justified in
terms of bond polarity and
arrangement of bonds about the
central atom.
Not Achieved
Achievement
Merit
Excellence
NØ
No response; no relevant evidence.
N1
Candidate provides any TWO statement for Achievement.
N2
Candidate provides any THREE statements for Achievement.
A3
Candidate provides any FOUR statements for Achievement.
A4
Candidate provides any FIVE statements for Achievement.
M5
Candidate provides ONE statements for Merit.
M6
Candidate provides BOTH statements for Merit.
E7
Candidate provides BOTH statements for Excellence with minor error in one aspect.
E8
Candidate provides BOTH statements for Excellence.
Q
TWO
(a)
(b)(i)
Evidence
Achievement
Type of
solid
Type of
particle
Attractive forces
molecular
molecules
intermolecular forces
metallic
atoms/cations
and electrons
Metallic bonding
Positive ions to electrons
covalent
network
atoms
covalent bonds
Copper atoms are held together in a 3–D lattice by metallic
bonding. Valence electrons are attracted to all neighbouring
atoms / cations (formed as the valence electrons are
delocalised).
Copper(II) chloride is made up of positive copper(II) ions and
negative chloride ions held together by strong electrostatic
attractions in a 3–D ionic lattice.
Copper chloride does not conduct electricity in the solid state
as the ions are not free to move around. When molten, the ions
are free to move and so molten copper chloride conducts
electricity. In copper metal the delocalised electrons / valence
electrons are free to move through the lattice; therefore the
metal is able to conduct electricity.
(ii)
The attraction of the positive Cu atoms for the valence
electrons is not in any particular direction, meaning Cu atoms
can move past one another without disrupting the metallic
bonding, and so Cu is malleable.
The ionic bonds in solid CuCl2 are directional so CuCl2 is
brittle. If pressure is applied to CuCl2 crystals, the repulsion
between like-charged ions will break the crystal apart.
Achievement with
Merit
Achievement with
Excellence
Explains why solid copper
conducts and why solid
copper(II) chloride does not
conduct.
Compares the electrical
conductivity of copper and
copper chloride with
reference to structure and
bonding.
Explains why copper is
malleable but copper(II)
chloride is brittle.
Justifies why copper is
malleable and copper(II)
chloride is brittle with
reference to structure and
bonding.
ONE row OR ONE column
correct.
Describes structure of copper
OR copper(II) chloride.
Describes conductivity in terms
of delocalised electrons
(copper) OR ions (copper(II)
chloride).
States metallic bonds are nondirectional OR Ionic bonds are
directional.
Potassium iodide is made up of
positive and negative ions.
Water is a polar solvent.
(c)
When potassium iodide dissolves in water the ionic lattice
breaks up. Water molecules are polar. The positive hydrogen
ends of the water molecules are attracted to the negative ions
(I–) in the lattice, and the negative oxygen ends of the water
molecules are attracted to the positive ions (K+).
The attraction of the polar water molecules for the ions is
sufficient to overcome the attractive forces between the K+
and I- ions and between the water molecules. This allows the
ions to be removed from the lattice. Hence potassium iodide
dissolves, forming separate K+ and I– ions in aqueous solution.
Not Achieved
Achievement
Merit
Excellence
NØ
No response; no relevant evidence.
N1
Candidate provides any TWO statements for Achievement.
N2
Candidate provides any THREE statements for Achievement.
A3
Candidate provides any FOUR statements for Achievement.
A4
Candidate provides any FIVE statements for Achievement.
M5
Candidate provides any TWO statement for Merit.
M6
Candidate provides ALL THREE statements for Merit.
E7
Candidate provides TWO statements for Excellence
E8
Candidate provides ALL THREE statements for Excellence
Explains solubility in terms
of attraction of cation or
anion to polar water
molecules.
Discusses solubility in
terms of structure and
bonding.
Q
Evidence
THREE
Exothermic:
(a)(i)
Change of state – liquid to solid. This process involves bond
forming which is exothermic
(ii)
(iii)
(b)
Achievement
Achievement with Merit
Achievement with
Excellence
THREE correct without reasons
OR TWO correct with reasons
Amount of Mg correct
Endothermic: Positive ΔrH value
Exothermic: Products have less energy than reactants
n(Mg) = 2.28 g / 24.3 g mol–1 = 0.0938 mol
ΔrH = ½ × 1200 kJ mol–1 × 0.0938 mol
ΔrH Equation correct with major
error (not dividing by 2)
Equation correct
(bonds broken) OR (bonds
formed) calculated correct with
error
ΔrH correct OR Energy released
correct with major error (not
dividing by 2).
ΔrH correct with working shown.
Either (bonds broken) OR
(bonds formed) calculated
correct
Energy released correct with
working shown.
ΔrH = -56.3 kJ
Therefore energy released = 56.3 kJ
(c)
ΔrH = (bonds broken) - (bonds formed)
= (5 × 412 + 360 + 463 + 348 + 3 × 496) – (4 × 743 + 6 x
463)
(or (5 × 412 + 360 + 348 + 3 × 496) – (4 × 743 + 5 × 463)
= 4719 - 5750 = -1031 kJ mol–1
= -1030 kJ mol–1
Not Achieved
Achievement
Merit
Excellence
NØ
No response; no relevant evidence.
N1
Candidate provides any ONE statement for Achievement.
N2
Candidate provides any TWO statements for Achievement.
A3
Candidate provides any THREE statements for Achievement.
A4
Candidate provides any FOUR statements for Achievement.
M5
Candidate provides any ONE statement for Merit.
M6
Candidate provides BOTH statements for Merit.
E7
Candidate provides BOTH statements for Excellence with minor error in one aspect.
E8
Candidate provides BOTH statements for Excellence.
Judgment Statement
Score Range
Not Achieved
Achieved
Merit
Excellence
0–6
7 – 12
13 – 18
19 – 24