Redox reactions​

• Involve oxidation and reduction

• Types of redox reaction:

  • ​Acid-base reactions

  • Precipitation reactions

  • Redox reactions

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Oxidation

• Old definition: Gain of oxygen

• New definition: Loss of electrons

• Increase in the oxidation number

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Reduction

• Old definition: Loss of hydrogen

• New definition: gain of electrons

• Decrease in the oxidation number

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Reducing agent

• The species that undergoes oxidation

Oxidizing agent

• The species that undergoes reduction 

Variable oxidation states

• Most of the transition metals have more than one oxidation state

• Most stable oxidation states are:

  • Sc​: +3

  • Ti: +4

  • V: +3, +4, +5

  • Cr: +2, +4, +6

  • Mn: +2, +7

  • Fe: +2, +3

  • Co: +2, +3

  • Ni: +2

  • Cu: +1, +2

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Half reactions

• Oxidation​

• Reduction​​

​​​Activities series

• Found in the data booklet

• Ranks metals according to the ease which they undergo oxidation

• Top (lithium) is more reactive

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Winkler method

• Technique  to measure the amount of dissolved oxygen in water

• High oxygen concentration--> low pollution

• BOD (biochemical Oxygen Demand) in ppm

Voltaic (galvanic) cells

• Convert chemical energy to electric energy

• Spontaneous, Exothermic process

• Oxidation happens in the Anode (negative electrode)

• Reduction happens in the Cathode (positive electrode)

Electrolytic cells

• Convert electric energy to chemical energy

• Non-spontaneous

• Oxidation happens in the Anode (positive electrode)

• 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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