Topic 9: Redox Processes
9.1 Oxidation and Reduction
Redox reactions​
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Involve oxidation and reduction
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Types of redox reaction:
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​Acid-base reactions
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Precipitation reactions
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Redox reactions
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Oxidation
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Old definition: Gain of oxygen
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New definition: Loss of electrons
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Increase in the oxidation number
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Reduction
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Old definition: Loss of hydrogen
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New definition: gain of electrons
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Decrease in the oxidation number
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Reducing agent
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The species that undergoes oxidation
Oxidizing agent
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The species that undergoes reduction
Variable oxidation states
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Most of the transition metals have more than one oxidation state
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Most stable oxidation states are:
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Sc​: +3
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Ti: +4
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V: +3, +4, +5
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Cr: +2, +4, +6
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Mn: +2, +7
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Fe: +2, +3
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Co: +2, +3
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Ni: +2
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Cu: +1, +2
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Half reactions
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Oxidation​

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Reduction​​

​​​Activities series
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Found in the data booklet
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Ranks metals according to the ease which they undergo oxidation
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Top (lithium) is more reactive
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Winkler method
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Technique to measure the amount of dissolved oxygen in water
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High oxygen concentration--> low pollution
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BOD (biochemical Oxygen Demand) in ppm

9.2 Electrochemical Cells
Voltaic (galvanic) cells
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Convert chemical energy to electric energy
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Spontaneous, Exothermic process
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Oxidation happens in the Anode (negative electrode)
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Reduction happens in the Cathode (positive electrode)
Electrolytic cells
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Convert electric energy to chemical energy
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Non-spontaneous
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Oxidation happens in the Anode (positive electrode)
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Reduction happens in the Cathode (negative electrode)
TIP: 1) In all electrochemical cells, oxidation happens in the anode and and reduction in the cathode. To remember: vowel with vowel and consonant with consonant. OARC
2) The positive and negative electrodes are the opposite in the electrolytic cells
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