9. Redox processes
9. Redox processes
9.1 Oxidation and reduction
Nature of science:
How evidence is used - changes in the definition of oxidation and reduction from one involving specific elements (oxygen and hydrogen), to one involving electron transfer, to one invoking oxidation numbers is a good example of the way that scientists broaden similarities to general principles.
Understandings:
Oxidation and reduction can be considered in terms of oxygen gain/hydrogen loss, electron transfer or change in oxidation number.
An oxidizing agent is reduced and a reducing agent is oxidized.
Variable oxidation numbers exist for transition metals and for most main-group non-metals.
The activity series ranks metals according to the ease with which they undergo oxidation.
The Winkler Method can be used to measure biochemical oxygen demand (BOD), used as a measure of the degree of pollution in a water sample.
Applications and skills:
Deduction of the oxidation states of an atom in an ion or a compound.
Deduction of the name of a transition metal compound from a given formula, applying oxidation numbers represented by Roman numerals.
Identification of the species oxidized and reduced and the oxidizing and reducing agents, in redox reactions.
Deduction of redox reactions using half-equations in acidic or neutral solutions.
Deduction of the feasibility of a redox reaction from the activity series or reaction data.
Solution of a range of redox titration problems.
Application of the Winkler Method to calculate BOD.
9.2 Electrochemical cells
Nature of science:
Ethical implications of research - the desire to produce energy can be driven by social needs or profit.
Understandings:
Voltaic (Galvanic) cells:
Voltaic cells convert energy from spontaneous, exothermic chemical processes to electrical energy.
Oxidation occurs at the anode (negative electrode) and reduction occurs at the cathode (positive electrode) in a voltaic cell.
Electrolytic cells:
Electrolytic cells convert electrical energy to chemical energy, by bringing about non-spontaneous processes.
Oxidation occurs at the anode (positive electrode) and reduction occurs at the cathode (negative electrode) in an electrolytic cell.
Applications and skills:
Construction and annotation of both types of electrochemical cells.
Explanation of how a redox reaction is used to produce electricity in a voltaic cell and how current is conducted in an electrolytic cell.
Distinction between electron and ion flow in both electrochemical cells.
Performance of laboratory experiments involving a typical voltaic cell using two metal/metal-ion half-cells.
Deduction of the products of the electrolysis of a molten salt.
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