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Topic 9: Redox Processes

9.1 Oxidation and Reduction
Essential Idea:
  • Redox (reduction–oxidation) reactions play a key role in many chemical and biochemical processes.
  • 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 & 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.
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.
PPT: Intro to Oxidation & Reduction
PPT: Redox Titrations & Winkler Method
Crash Course: Redox Reactions
Activity Series Interactive Activity
Visualizing Redox Reactions
Balancing Redox Reactions Interactive
Khan Academy: Redox Titrations
Thornley Video: The Winkler Method To Calculate BOD
9.2 Electrochemical Cells
Essential Idea:
  • Voltaic cells convert chemical energy to electrical energy and electrolytic cells convert electrical energy to chemical energy.
  • Voltaic (Galvanic) cells:
    • oltaic 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 & 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.
Nature of Science:
  • Ethical implications of research—the desire to produce energy can be driven by social needs or profit.
PPT: Electrochemical Cells
Crash Course: Electrochemistry
Activity Series Interactive Activity
Video: Voltaic vs. Electrolytic Cells
How to Charge an iPod with fruits
Voltaic Cell Online Simulation
Animation of Voltaic Cells
Voltaic Cell Simulator