Topic 9 Oxidation and reduction SL
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Essential ideas:
- Redox (reduction–oxidation) reactions play a key role in many chemical and biochemical processes.
- Voltaic cells convert chemical energy to electrical energy and electrolytic cells convert electrical energy to chemical energy.
9.1 Definitions of oxidation and reduction
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Understandings:
Oxidation and reduction can be considered in terms of oxygen gain/hydrogen loss, electron transfer or change in oxidation number. |
9.1 Oxidation states
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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. Note - Oxidation number is shown by a Roman numeral after the name or symbol of the element. |
9.1 Oxidizing and reducing agents
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Understandings:
An oxidizing agent is reduced and a reducing agent is oxidized. Applications and skills: Identification of the species oxidized and reduced and the oxidizing and reducing agents, in redox reactions. |
An oxidising agent is so-called because it oxidises another species and therefore undergoes reduction. A reducing agent reduces another species and undergoes oxidation. Metals higher up in the activity series are stronger reducing agents and those lower down are weaker reducing agents. The strength of the halogens as oxidising agents decreases as you go down the group; fluorine is the strongest oxidising agent in group 17 and iodine is the weakest.
9.1 Writing net ionic equations
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This video covers to write net ionic equations for redox reaction.
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9.1 Disproportionation reactions
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This video covers disproportionation reactions.
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9.1 The activity series
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Understandings:
The activity series ranks metals according to the ease with which they undergo oxidation. Application and skills: Deduction of the feasibility of a redox reaction from the activity series or reaction data. |
9.1 Balancing redox equations in acidic solutions
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Applications and skills:
Deduction of redox reactions using half-equations in acidic or neutral solutions. |
9.1 Redox titration
9.1 The Winkler method
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Understandings:
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: Application of the Winkler Method to calculate BOD. |
9.2 Voltaic cells
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Understandings:
Oxidation occurs at the anode (negative electrode) and reduction occurs at the cathode (positive electrode) in a voltaic 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. Distinction between electron and ion flow in voltaic cells. |
9.2 Cell diagram convention
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Guidance:
For voltaic cells, a cell diagram convention should be covered |
9.2 Electrolytic cells
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Understandings:
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 current is conducted in an electrolytic cell. Distinction between electron and ion flow in both electrochemical cells. Deduction of the products of the electrolysis of a molten salt. |
9.2 Comparison of electrochemical cells
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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 cells. |