CHEMISTRY - 2.6
(Describe principle of chemical reactivity)
ASSESSMENT SCHEDULE NZIC 2006
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)
Effect: Slows the production
Expl: Particle movement is slower therefore fewer
collisions.
ii) Effect: No change
Expl: As the concentration of HNO3 particles has
not increased, the collision rate remains
unchanged.
iii) Effect: Speeds up the production
Expl:Higher concentration / more particles of
HNO3 in a given volume means more collisions
b)
Achievement
All 3 effects
correct
Merit
Two of the
three
explanations
correct
Excellence
All correct
Reactants
Energy
Activation
energy
H
Products
Reaction coordinate
c)
Exothermic
∆H is negative
or
energy is being lost from the system
Correct choice
and explanation
d)
By providing an alternate pathway of a lower
activation energy.
Correct
The equilibrium is maintained by a balance in two
opposing processes (or similar).
Correct
i)
Observation
correct
TWO
a
b
Obs:
Colour fades / lightens
Expl:
Cooling favours the exothermic /
reverse reaction
or
the equilibrium shifts to the left
This is an endothemic reaction so the system
reacts to produce heat to minimise the change.
Observation
plus limited
explanation,
such as either
of the
underlined
sections
Observation
and full
explanation
Evidence
TWO
b)
cont’d
(ii) Obs:Colour fades / lightens
Expl:
Increase in pressure favours the
reaction that forms the smaller number of
molecules
or
Increase in pressure causes the equilibrium to
shift to the left
The system reacts to reduce the pressure by
forming fewer moles of gas.
(iii) K c 
THREE
a)
NO2 2
N 2O 4 
Achievement
Observation
correct
Merit
Observation
plus limited
explanation,
such as either
of the
underlined
sections
Correct
(iv) No change
Kc does not change with a change in pressure /
is constant at a constant temperature
Correct choice
Correct
choice and
explanation
M(Al) = 27 g mol–1
Allow one error
only.
Eg:
mathematical or
missing negative
or does not
multiply by 2
Correct
answer
One step correct
Allow one
error only
4 out of 6 correct
All correct
4 .2
= 0.156 moles gives 137.6kJ
27
2 moles would give
2
137.6
= 1764.1kJ
0.156
Excellence
Observation
and full
explanation
So ∆Ho = –1764.1 kJ mol–1
b)
M(Al2O3) = 102 g mol–1
Since 1 mole Al2O3 formed when 1764.1 kJ released,
89
= 0.0505 moles formed when 89kJ
1764.1
released
0.0505  102 = 5.151 g
FOUR
i) 1  10–8
ii) 8
iii) 2.86  10–13
iv) 1.46
v) 3.16  10–10
vi) 3.16 x 10-5
Correct
answer with
unit and three
significant
figures
Evidence
FIVE
a)
b)
Achievement
i, ii and iv
Only correct
reactions chosen
i)
One row correct
for one equation
acid/base pair
acid
base
HCl / Cl–
HCl
Cl–
H2O/ H3O+
H3O+
H2O
acid
base
Merit
Excellence
Both rows
correct for
one equation
or
ii)
acid/base pair
+
+
NH4 / NH3
NH4
OH– / H2O
H2O
NH3
OH–
acid/base pair
acid
base
H3O+ / H2O
H3O+
H2O
H2O
OH–
or
iv)
–
OH / H2O
c)
i) Acid is a proton donor.
Correct
ii)
Identifies acid in
each reaction
or
identifies the
acid and base in
one reaction.
Identifies
acids and
bases in both
reactions.
One equation
and statement
correct
Complete
answer
In reaction (i) H2O is a acid / proton donor and
HCO3– is a base / proton acceptor.
In reaction (ii) HCO3– is acid / donor, H2O is
base / acceptor
Both HCO3– and H2O can react as acids or bases. (If
term amphiprotic is used it must be explained)
d)
SIX
a)
b)
c)
NH3 + H2O
NH4+ + OH–
Solution is basic
NH4+ + H2O
NH3 + H3O+
Solution is acidic
An acid that only partially reacts with water / donates
only a few protons to water molecules in an aqueous
solution.
Add universal indicator; HNO3 has a lower pH
or
test both acids with Marble chips or Mg ribbon HNO3 will react faster.
HNO3 solution would contain only H3O+ ions and
NO3– ions as HNO3 is a strong acid and completely
reacts with water.
HNO3 + H2O
NO3- + H3O+
CH3COOH is a weak acid which only partially reacts
with water so its solution would contain mainly
CH3COOH molecules, with a relatively few H3O+ ions
and CH3COO– ions. (H2O molecules and OH– ions
are not required)
CH3COOH + H2O
CH3COO– + H3O+
Merit and
includes
underlined
explanation
Correct
A correct test
chosen
Correct test
and
observation
Correctly
identifies species
for one solution
Correctly
identifies
species for
both solutions
Correct
composition
of both
solutions plus
accurate
explanation
and correct
equations
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.
Achieved
A total of ELEVEN opportunities correct at the Achieved level or higher
Merit
A total of THIRTEEN opportunities correct; 6 at the Merit level or higher and 7 at the
Achieved level or higher.
Excellence
A total of FIFTEENs opportunities correct; 3 at the Excellence level, 7 at the Merit level or
higher and 5 at the Achieved level or higher.