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Chemistry 3.3 Describe oxidation–reduction processes

Achievement criteria

The level of achievement that you will reach is decided by the way you answer each question about oxidation–reduction processes. The key words are describe, explain and apply, and discuss oxidation–reduction processes.

Achievement

• Describe oxidation–reduction processes.

This involves identifying, naming, defining, drawing, giving features of, outlining, and/or carrying out simple calculations.

Make sure you can:

• determine oxidation numbers
• balance a reduction-oxidation equation, given the products and reactants
• use reduction potentials to predict reactivity
• recall the formulae and colours of reactants and their respective products for the reductants and oxidants listed in the Achievement Standard
• recognise that a negative E^o cell value for a proposed reaction means it is not spontaneous
• recognise that electrons flow through the external circuit from the negative to positive terminal in an electrochemical cell and that flow of ions is needed to maintain charge neutrality in each half-cell
• use the results of reactions between metals and metal ions to determine which was the strongest and which was the weakest reductant.

Achievement with Merit

• Explain and apply oxidation–reduction processes.

This involves describing as well as justifying, clarifying, giving reasons for, giving an account of, making links and/or carrying out calculations.

Make sure you can:

• meet the criteria for Achievement
• link the reactions of species to the observed colour changes and the species formed
• write a balanced reduction-oxidation equation with no provided formulae
• show a depth of understanding of how a galvanic cell operates
• identify and explain the role of reductant and oxidant
• use oxidation numbers to identify a reductant and oxidant in a reaction
• correctly link the reactions between metals and metal ions to the various reduction potentials and the strength of the metals as reductants
• identify incorrectly set up cells and discuss reasons for their failure to work, with suggestions for improvement
• write a balanced equation for a cell reaction and use this correctly to calculate the moles produced at one electrode given the mass decrease at the other.

Achievement with Excellence

• Discuss oxidation–reduction processes.

This involves evaluating, reviewing, analysing, interpreting, relating, comparing, and contrasting/or calculating.

Make sure you can:

• meet the criteria for Merit
• use standard reduction potentials to predict the spontaneity of a reaction
• use electrochemical principles in applied contexts
• give answers in full, without error or irrelevant detail – Excellence is the ability to follow through on all equations, calculations, and observations.

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