National Certificate of Educational Achievement
2010 Assessment Report
Chemistry Level 2
90308
Describe the nature of structure and bonding in different substances
90309
Describe the structural formulae and reactions of compounds
containing selected organic functional groups
90310
Describe thermochemical and equilibrium principles
90311
Describe oxidation-reduction reactions
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NCEA Chemistry Level 2 Assessment Report, 2010 – page 2 of 8
COMMENTARY
To be successful in Chemistry at Level 2, candidates need to ensure that they attempt all parts of all
questions as all levels of attainment are available in each question. A question that may start with
the word Discuss will have opportunities for Achievement, Achievement with Merit as well as
Achievement with Excellence.
Terms in chemistry have specific meanings, but some candidates used terms carelessly. For
example solutions with no colour should be described as colourless, not ‘clear’. Similarly, an ionic
substance cannot be also described as molecular or polar.
Successful candidates showed a clear understanding of concepts and were able to use their ideas in
a range of contexts. They were less likely to produce answers that were contradictory.
STANDARD REPORTS
90308
Describe the nature of structure and bonding in different substances
ACHIEVEMENT
Candidates who were awarded Achievement for this standard demonstrated the required
skills and knowledge. They typically:
• drew Lewis structures correctly
• named shapes corresponding to Lewis structures
• described the number of negative charge regions around a central atom or determined a correct
bond angle
• described observations when a charged rod was brought close to a liquid stream
• identified the polarity of a molecule given a Lewis structure
• described a polar bond in terms of the electronegativity difference between atoms
• described the particles and attractive forces in a solid given the name, formula or particle
representation of that solid
• described the bond angles in a molecule
• described the metallic bond
• understood that mobile charged particles are needed for conducting electricity.
NOT ACHIEVED
Candidates who were assessed as Not Achieved for this standard lacked some or all of the
skills and knowledge required for the award of Achievement. They typically:
• omitted non-bonding electrons in Lewis structures
• confused the terms trigonal pyramid and trigonal planar
• did not give correct bond angles
• did not differentiate between bond and molecule polarity
• used electronegativity in relation to molecules instead of atoms
• assigned full charges to atoms in molecules
• used the term ‘react with’ incorrectly.
• used the word ‘dipole’ incorrectly
• described all substances as molecular or as having molecular bonding
• could not identify particles in solids correctly
• described ionic substances as being polar
NCEA Chemistry Level 2 Assessment Report, 2010 – page 3 of 8
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described silica as if it was diamond or graphite consisting of carbon atoms
linked non-directional to atoms or electrons instead of linking it to the bonds in metals
linked electrical conductivity to ions or electrons but their movement was not mentioned or
implied
did not know how a charged rod affects polar and non polar liquids
described malleability instead of ductility.
ACHIEVEMENT WITH MERIT
In addition to the skills and knowledge required for the award of Achievement, candidates
who were awarded Achievement with Merit typically:
• linked bond angle or molecule shape to the number and nature of negative charge regions
around the central atom in a molecule
• linked the polarity of a molecule to its shape or the arrangement of polar bonds
• linked melting point or solubility to particles and the strength of attractive forces in a particular
solid
• linked electrical conductivity of a metal to its structure
• linked ductility of a metal to the non-directional nature of the metallic bond
• linked electronegativity difference of constituent atoms to bond polarity.
ACHIEVEMENT WITH EXCELLENCE
In addition to the skills and knowledge required for the award of Achievement with Merit,
candidates who were awarded Achievement with Excellence typically:
• discussed fully, the factors determining the shape of molecules and correct bond angles,
including the nature and number of negative charge regions repelling around the central atom
• discussed fully, the factors that determine the polarity of a molecule including electronegativity
difference between bonding atoms, molecule shape, and the arrangement of the polar bonds or
dipoles
• discussed fully, the melting point and solubility of an ionic solid and covalent network solid in
terms of the constituent particles and the strength and nature of attractive forces between the
particles
• discussed fully, the electrical conductivity and ductile properties of copper by describing the
particles and attractive forces in copper and linking these to both properties.
OTHER COMMENTS
It is not necessary for candidates to learn individual electronegativity values. Candidates should
focus on an understanding of electronegativity and use it to interpret specific situations.
The structure of metals, with delocalised electrons being attracted to the nuclei of neighbouring
atoms, is not clearly understood.
Some candidates contradicted themselves in their answers, especially when explaining solubility,
for example, ionic MgCl2 became polar.
Some candidates wrote about atoms repelling instead of regions of negative charge repelling.
NCEA Chemistry Level 2 Assessment Report, 2010 – page 4 of 8
90309
Describe the structural formulae and reactions of compounds
containing selected organic functional groups
ACHIEVEMENT
Candidates who were awarded Achievement for this standard demonstrated the required
skills and knowledge. They typically:
• named and drew appropriate organic structures
• identified and drew cis-trans isomers
• identified some types of reactions
• classified alcohols correctly
• drew a polymer structure given the monomer
• recognised the Markovnikov addition rule
• identified products of addition reactions
• recognised observations of simple chemical tests for organic compounds.
NOT ACHIEVED
Candidates who were assessed as Not Achieved for this standard lacked some or all of the
skills and knowledge required for the award of Achievement. They typically:
• were unable to draw organic structures accurately
• did not identify cis-trans isomers from the given structural formulae
• confused different types of organic reaction
• could not identify types of alcohol structure
• failed to describe simple chemical tests for organic molecules.
ACHIEVEMENT WITH MERIT
In addition to the skills and knowledge required for the award of Achievement, candidates
who were awarded Achievement with Merit typically:
• identified the criteria required for organic molecules to exhibit cis-trans isomerism
• explained addition reactions and identified products of such reactions
• identified some of the products of the hydrolysis of a triglyceride
• linked observations in simple chemical tests to differing organic molecules.
ACHIEVEMENT WITH EXCELLENCE
In addition to the skills and knowledge required for the award of Achievement with Merit,
candidates who were awarded Achievement with Excellence typically:
• discussed structural and geometrical isomerism and linked the discussion to given molecular
structures
• gave a full explanation of addition reactions, including Markovnikov addition and wrote correct
structural formulae for three examples
• identified and drew structural formulae for all the products of alkaline hydrolysis of a
triglyceride
• produced a valid method for identifying different organic compounds using simple chemical
tests, and drew structural formulae for the organic products from each test.
NCEA Chemistry Level 2 Assessment Report, 2010 – page 5 of 8
OTHER COMMENTS
There was a misconception that UV light would influence the reaction of acidified potassium
permanganate with an alkene.
A number of candidates thought that rotation could occur around the double bond.
Some candidates used the word clear when they meant colourless.
The description of a colour change should include both the starting and finishing colours.
90310
Describe thermochemical and equilibrium principles
ACHIEVEMENT
Candidates who were awarded Achievement for this standard demonstrated the required
skills and knowledge. They typically:
• identified factors that affected reaction rates
• predicted the effect changes in conditions had on reaction rates
• understood that changes in the number of particles or collisions affected the reaction rate
• recognised that the concentration of a strong acid or base was equal to the concentration of the
hydronium or hydroxide ions
• described a weak acid and one which partially dissociates
• recognised that a basic salt forms hydroxide ions
• identified exothermic or endothermic reactions and used data to predict if the reaction was
exothermic or endothermic
• predicted the effect changes in conditions have on equilibrium reactions
• calculated the amount of ammonia correctly from mass and molar mass
• wrote correct equilibrium expressions
• related species concentration to Kc values.
NOT ACHIEVED
Candidates who were assessed as Not Achieved for this standard lacked some or all of the
skills and knowledge required for the award of Achievement. They typically:
• misunderstood the meaning of key words such as “factor” in relation to reaction rates
• could not explain concentration
• did not identify particles or collisions as important factors in why reaction rates change
• were unable to calculate pH for acid concentration
• used pH as the sole predictor of acid strength
• could not identify a basic salt
• could not distinguish between exothermic and endothermic reactions
• explained changes to equilibrium reactions using collision theory
• confused reaction directions e.g. left with right or forward with reverse
• substituted numbers into formulae incorrectly or inverted the formulae
• could not write an equilibrium constant expression.
NCEA Chemistry Level 2 Assessment Report, 2010 – page 6 of 8
ACHIEVEMENT WITH MERIT
In addition to the skills and knowledge required for the award of Achievement, candidates
who were awarded Achievement with Merit typically:
• identified factors affecting reaction rates and their effects
• explained concentration in terms of particle per unit volume or reaction rate in terms of collision
per unit time
• calculated the concentration of hydronium ions, hydroxide ions or pH given the concentration of
a strong acid or base
• related pH to the acid concentration and the degree of dissociation for weak acids
• wrote equations to explain how a basic salt produces hydroxide ions
• used equilibrium principles to explain changes in equilibrium reactions
• carried out two-step calculations, but often rounded too early leading to inaccurate answers
• explained the significance of Kc on the relative concentration of reactants and products
• made appropriate links between Kc and temperature change.
ACHIEVEMENT WITH EXCELLENCE
In addition to the skills and knowledge required for the award of Achievement with Merit,
candidates who were awarded Achievement with Excellence typically:
• discussed concentration in terms of particle per unit volume and reaction rate in terms of
collision per unit time
• calculated the concentration of hydronium ions or hydroxide ions, or pH given the concentration
of a strong acid or base with appropriate use of significant figures and units. Also rounded their
answers at the end of the calculation only
• justified choices as to the relative weakness of acids using concentration and pH data
• explained fully, how a basic salt produces a basic solution, with equations
• used Le Chatelier’s Principle to predict and justify how changes in pressure and concentration
affect equilibria
• explained the effect of temperature on an equilibrium system given Kc data.
90311
Describe oxidation-reduction reactions
ACHIEVEMENT
Candidates who were awarded Achievement for this standard demonstrated the required
skills and knowledge. They typically:
• calculated oxidation numbers correctly
• identified the mistake in an incorrectly balanced half-equation
• identified the oxidant in an equation with some reasoning
• recalled some learned ideas about electrolysis
• identified which species were undergoing oxidation and reduction in common redox reactions
• described the appearance of some species in redox reactions
• balanced simple redox half-equations.
NCEA Chemistry Level 2 Assessment Report, 2010 – page 7 of 8
NOT ACHIEVED
Candidates who were assessed as Not Achieved for this standard lacked some or all of the
skills and knowledge required for the award of Achievement. They typically:
• could not identify an oxidant in a given reaction, or did not give a valid reason for their correct
choice
• did not demonstrate a clear understanding of the equation balancing process, or wrote simple
balanced half-equations
• confused oxidant with oxidation
• assigned oxidation numbers incorrectly
• could not identify a mistake in an incorrectly balanced half-equation
• reversed the terminology or processes of electrolysis, or lacked understanding of electrolysis
• did not identify the products of common oxidation and reduction reactions, or the appearance of
species involved.
ACHIEVEMENT WITH MERIT
In addition to the skills and knowledge required for the award of Achievement, candidates
who were awarded Achievement with Merit typically:
• wrote correctly balanced half-equations
• identified an oxidant and gave a valid reason for this, with reference to oxidation numbers
• explained why an equation balanced incorrectly could not be combined into an overall balanced
equation, in terms of oxidation-reduction principles and electron transfer
• explained the electrolysis of zinc chloride in terms of the movement of ions, the processes at
each electrode and observations
• explained reactions between a common oxidant and two common reductants, wrote halfequations and linked experimental observations to the species involved.
ACHIEVEMENT WITH EXCELLENCE
In addition to the skills and knowledge required for the award of Achievement with Merit,
candidates who were awarded Achievement with Excellence typically:
• addressed all aspects of every question
• used correct formulae to identify species correctly and linked them to experimental observations
• identified an oxidant and discussed this in terms of the oxidation numbers, and oxidation and
reduction processes involved
• discussed why an equation balanced incorrectly could not be combined into an overall balanced
equation in terms of oxidation-reduction principles, electron transfer and charge
• discussed the electrolysis of zinc chloride, including movement of electrons through the
external circuit
• discussed details of two redox reactions including half and overall equations, and initial and
final observations linked to the species involved.
OTHER COMMENTS
Giving incorrect formulae was common when referring to species e.g. Cr2O7 and Cr2+
Candidates confused the terms; electron and charge when discussing the balancing of an equation,
or failed to recognise the contribution of ionic species to the overall charge.
NCEA Chemistry Level 2 Assessment Report, 2010 – page 8 of 8
Many candidates misread the question or wrongly anticipated what it would be asking, and
commonly identified the species that would be moving to the anode and cathode, rather than the
substances formed there.