Exemplar for internal assessment resource Chemistry 3.7A for Achievement Standard 91393
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Exemplar for Internal Assessment Resource
Chemistry Level 3
Resource title: Making Copper
This exemplar supports assessment against:
Achievement Standard 91393
Demonstrate understanding of oxidation-reduction processes
Student and grade boundary specific exemplar
The material has been gathered from student material specific to an A or B assessment
resource.
Date version published by
Ministry of Education
© Crown 2012
December 2012
To support internal assessment from 2013
Exemplar for internal assessment resource Chemistry 3.7A for Achievement Standard 91393
Grade Boundary: Low Excellence
1.
To achieve at Excellence level students are expected to demonstrate a comprehensive
understanding of oxidation-reduction processes. This involves comparing and
contrasting and justifying links between oxidation-reduction processes, observations,
equations and calculations. This requires the consistent use of chemistry vocabulary,
symbols and conventions.
Links between the spontaneity of the reactions using reduction potentials and the
changes in colour and state are made. Reactions of both cells are compared and
contrasted (1).
Chemistry vocabulary is used consistently except for the calculation of a cell potential
for the electrolytic cell (2). However, there is part explanation (electrolytic cell) of why
the reaction is spontaneous/non-spontaneous by referring to relative strengths of
oxidants and reductants (3).
To meet Excellence more securely, comprehensive understanding must ensure that a
full explanation (for both cells) of why the reaction is spontaneous/non-spontaneous by
referring to relative strengths of oxidants and reductants.
© Crown 2012
Exemplar for internal assessment resource Chemistry 3.7A for Achievement Standard 91393
Grade Boundary: High Merit
2.
To achieve at Merit level students are expected to demonstrate an in-depth
understanding of oxidation-reduction processes. This involves making and explaining
links between oxidation-reduction processes, observations, equations and calculations.
This requires explanations that use chemistry vocabulary, symbols and conventions.
There is sufficient explanation as to what has been oxidised and reduced in terms of
oxidation number or electron loss/gain (1). Full, completely balanced equations have
been written for oxidation-reduction reactions occurring (2).
Explanations of oxidation-reduction processes for the electrochemical cell are
supported by a conventional cell diagram and cell potential calculation. There is
justification as to why the reactions occurring in the electrochemical cell are
spontaneous (3).
To meet Excellence, justification as to why the electrolysis of copper chloride to
produce copper is non-spontaneous is required.
© Crown 2012
Exemplar for internal assessment resource Chemistry 3.7A for Achievement Standard 91393
Grade Boundary: Low Merit
3.
To achieve at Merit level students are expected to demonstrate an in-depth
understanding of oxidation-reduction processes. This involves making and explaining
links between oxidation-reduction processes, observations, equations and calculations.
This requires explanations that use chemistry vocabulary, symbols and conventions.
There is sufficient explanation as to what has been oxidised and reduced in terms of
oxidation number or electron loss/gain (1). Half equations have been written (2). A cell
diagram has been written for the electrochemical cell and the cell potential has been
calculated (3).
There is an attempt to make and explain links between oxidation-reduction processes,
observations and calculations. However, there is no full equation for the electrolytic cell
and there are some inaccuracies in the use of chemistry vocabulary and conventions.
To meet Merit more securely, links between oxidation-reduction processes must be
explained using correct chemistry vocabulary and conventions, and a full equation for
the electrolytic cell must be provided.
© Crown 2012
Exemplar for internal assessment resource Chemistry 3.7A for Achievement Standard 91393
Grade Boundary: High Achieved
4.
To Achieve this standard students must demonstrate understanding of oxidationreduction processes. This involves describing oxidation-reduction processes and may
involve calculations. This requires the use of chemistry vocabulary, symbols and
conventions.
Reactants and products of oxidation-reduction have been named and half equations
have been written for electrolysis and electrochemical reactions (1).
Explanations for oxidation-reduction have been provided and supported by a cell
calculation for the electrochemical cell, but there is no conventional cell diagram for the
electrochemical cell (2). Also, there is no making of and explanation of links between
the oxidation-reduction processes, observations and equations.
To meet Merit, making and explaining links between oxidation-reduction processes is
required.
© Crown 2012
Exemplar for internal assessment resource Chemistry 3.7A for Achievement Standard 91393
Grade Boundary: Low Achieved
5.
To Achieve this standard students must demonstrate understanding of oxidationreduction processes. This involves describing oxidation-reduction processes and may
involve calculations. This requires the use of chemistry vocabulary, symbols and
conventions.
Reactants and products have been named. Half equations have been written which
show electron loss/gain (1). However, the oxidation number of the chloride ion has
been incorrectly identified as -2 and the description of change of oxidation number is
not correct for the oxidation process in the electrolytic cell (2).
For a more secure Achievement, the correct description of oxidation number change
for all couples is required.
© Crown 2012
Exemplar for internal assessment resource Chemistry 3.7A for Achievement Standard 91393
Grade Boundary: High Not Achieved
6.
To Achieve this standard students must demonstrate understanding of oxidationreduction processes. This involves describing oxidation-reduction processes and may
involve calculations. This requires the use of chemistry vocabulary, symbols and
conventions.
Reactants and products of the reduction couple only have been correctly named for
electrolysis of CuCl2 (1). For the oxidation process (in the electrolytic cell), oxygen gas
(instead of chlorine gas) has been incorrectly identified as the product from the
oxidation of water (2). Oxidation-reduction processes for the electrochemical cell have
been correctly described (3).
Half equations have been written correctly for the electrochemical reaction only.
Oxidation number change has been described and the oxidation-reduction process in
terms of electron loss/gain is described for the electrochemical cell only (4).
To meet Achievement, oxidation-reduction processes in the electrolytic cell must be
described correctly.
© Crown 2012