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NCEA Level 3 Science (90730) 2012 — page 1 of 3
Assessment Schedule – 2012
Science: Describe selected organic compounds and their uses (90730)
Evidence Statement
Q
ONE
(a)
Evidence
Pentane structure
CH3(CH2)3CH3
Achievement
TWO of:
Structures.
OR
Pent-1-ene structure
CH3CH2CH2CH=CH2
Description of
molecule shape/
bonding between
molecules.
OR
Degree of
saturation for
margarine or
canola oil.
Alkanes have zigzag (straight) carbon chains
where the carbon atoms rotate freely which
results in chains that fit closely together with
stronger bonding between chains. As a result,
alkanes have higher melting points, as more
energy is needed to break the chains apart.
Alkenes are more bulky, as the C=C double bond
is a fixed point in the molecule (it does not allow
free rotation). Therefore alkenes do not fit
together as closely, so the bonds between the
chains are not as strong and therefore they have
lower melting points. Less energy is required to
break the chains apart.
(b)
canola oil + hydrogen  margarine
Canola oil is polyunsaturated ie has many double
bonds within the molecules. In margarine some
of the C=C double bonds have taken part in the
addition reaction above. The hydrogenation
reaction has added hydrogen to the carbons in the
double bond, resulting in a more saturated
molecule.
The saturated molecule fits together more
closely; the forces between the molecules are
stronger, resulting in a higher melting point. This
results in a harder (solid at room temperature)
product, due to its higher melting point.
Achievement
with Merit
Description of
molecule shape
and
bonding between
molecules.
OR
Degree of
saturation for
margarine or
canola oil.
AND
Reason(s) for the
difference in
melting points.
Achievement
with Excellence
An integrated
answer that
includes:
Description of
molecule shape
related to
structures and
bonding between
molecules;
AND
Degree of
saturation for
margarine or
canola oil linked
to different
bonding between
molecules,
leading to
different melting
points and
physical
properties: solid/
semisolid.
NCEA Level 3 Science (90730) 2012 — page 2 of 3
TWO
Completed equation:
Glycerol + 3 stearic acid 
triglyceride + 3 water
TWO of:
• Equation:
complete word
equation or
correct symbols
for products.
• Functional group
indicated
showing bonds
(Ie, not just
COOC.)
• Names type of
reaction.
Names type of
reaction.
OR
Functional group
indicated
showing bonds.
AND
Word or symbol
equation
complete.
Word or symbol
equation
complete and
balanced
showing
equilibrium
arrow (or text
describes
equilibrium).
AND
Functional group
indicated.
OR
AND
• Identifies water
as the other
product.
Type of reaction: Condensation / Esterification
Special conditions for high yield: Heated under
reflux conditions in the presence of conc. H2SO4.
Reflux allows heating of volatile reactants to
occur over a long period of time, with a greater
yield resulting.
Concentrated H2SO4 acts as:
• A catalyst, which speeds up a reaction without
itself being used up in the reaction.
• A dehydrating agent, which removes the water
produced from the reaction.
The esterification reaction is a dynamic
equilibrium reaction, both the forward and the
reverse reactions are occurring at the same time.
Removing one of the products moves the
position of equilibrium favouring the forward
reaction and production of a greater yield of
triglyceride.
• Identifies either
special
condition.
Identifies either
of the special
conditions and
explains how it
contributes to a
greater yield of
triglycerides.
Names type of
reaction.
AND
Identifies both
special
conditions and
discusses how
they contribute
to a greater yield
of triglyceride.
NCEA Level 3 Science (90730) 2012 — page 3 of 3
THREE
Degree of saturation refers to whether a molecule
has lots of C=C double bonds. Fats are two types,
saturated (no double bonds) unsaturated (some
double bonds, monounsaturated = one and
polyunsaturated = many).
Iodine number shows how unsaturated fats and
oils are.
Iodine readily reacts with the C=C double bond
in unsaturated molecules resulting in a
haloalkane. If a lot of iodine reacts, then the
sample had a lot of double bonds. This would
generally result from a sample that has a low
melting point. If the iodine number is low (less
iodine reacts), then there were not as many
double bonds in the sample. This sample would
generally have a higher melting point.
As sardines have a very large iodine number of
185 this shows the oil has a large number of C=C
double bonds. Sardines live in very cold water so
need to have oil that is liquid at a low
temperature. A very high degree of saturation
ensures a very low melting point which allows
fish to live at low temperatures.
Describes degree
of saturation.
Explains degree
of saturation.
OR
AND
Describes iodine
number.
Explains iodine
number linked to
degree of
saturation (can
be in the form of
a diagram /
equation).
OR
Describes high
iodine number
means high level
of unsaturation
OR
Describes why
sardines need
liquid oil.
Discusses how
the iodine
number links to
the degree of
saturation and
why sardines
require a high
iodine number,
in terms of
flexibility of fish
in cold water.
(Accept cis /
trans
comparison.)
OR
Explains why
sardines need
liquid oil.
OR
Explains that a
high iodine
number
characterises
plants and these
have unsaturated
oils.
Judgement Statement
Achievement
Achievement with Merit
Achievement with Excellence
2A
2M
2E
OR
1E+2M
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