Cells and half cells

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  • 1. Chemistry
    Cells and Half Cells
  • 2. Definition
    An electrochemical cell controls the electron transfer to produce electrical energy
    A half cell comprises of an element in two oxidation states
    The electrode potential of the half cell indicates its tendency to lose or gain electrons
  • 3. Example
  • 4. Cells from metal/metal ion half cells
    • The difference in electrode potential is measured with a voltmeter
    • 5. The wire allows electrons to be transferred between the half cells
    • 6. The salt bridge allows ions to be transferred between the half cells
    • 7. A salt bridge can be made out of a strip of filter paper soaked in an aqueous solution of an ionic compound that doesn’t react with the half cell solutions
    • 8. Usually aqueous KNO₃ (aq) or NH₄NO₃ (aq) is used
  • Non-metal/non-metal ion half cells
    Problem
    There is no electrode to connect wire to
    Solution
    A platinum electrode is placed in the solution
    The platinum doesn’t react at all
    Its purpose is to allow the transfer of electrons in and out of the half cell
    The surface of the platinum electrode is coated with platinum black
  • 9. Metal ion/metal ion half cell
    Fe²⁺ (aq) + e⁻ ↔ Fe³⁺ (aq)
    Cell is made up of:
    A solution containing Fe²⁺ (aq) and Fe³⁺ (aq) ions of the same concentration
    Also known as Equimolar
    Inert platinum electrode with a connecting wire