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Oxidation and Reduction Concepts

Key Concepts

  • Oxidation: an atom or ion loses electrons

  • Reduction: an atom or ion gains electrons

  • In an oxidation reaction, the atom or ion becomes more positive due to the loss of electrons.

  • In a reduction reaction, the atom or ion beomes more negative due to the gain of electrons.

Examples

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Oxidation Reactions

  1. Consider the reaction Na → Na+ + e

    A neutral sodium atom loses an electron to produce a positively charged sodium ion (cation)

    The sodium atom has been oxidised because it has lost an electron.

    The charge on sodium has been increased from 0 for the neutral atom to 1+ for the sodium ion (Na+).

    Sodium has become more positive.

  2. Consider the reaction Cu+ → Cu2+ + e

    A copper ion with a charge of 1+ loses an electron to produce a copper ion with a charge of 2+

    Cu+ has been oxidised because it has lost an electron.

    The charge on copper has been increased from 1+ for the Cu+ ion to 2+ for the Cu2+ ion.

    Copper has become more positive.

  3. Consider the reaction Pb2+ → Pb4+ + 2e

    A lead ion with a charge of 2+ loses 2 electrons to produce a lead ion with a charge of 4+

    Pb2+ has been oxidised because it has lost 2 electrons.

    The charge on lead has been increased from 2+ for the Pb2+ ion to 4+ for the Pb4+ ion.

    Lead has become more positive.

Reduction Reactions

  1. Consider the reaction F + e → F-

    A neutral fluorine atom gains an electron to form the negatively charged fluoride ion (anion)

    The fluorine atom has been reduced because it has gained an electron.

    The charge on fluorine has decreased from 0 for the neutral atom to 1- for the fluoride ion.

    Fluorine has become more negative.

  2. Consider the reaction O + 2e → O2-

    A neutral oxygen atom gains 2 electrons to form the negatively charged oxide ion (O2-)

    The oxygen atom has been reduced because it has gained 2 electrons.

    The charge on oxygen has decreased from 0 for the neutral atom to 2- for the oxide ion (O2-) .

    Oxygen has become more negative.

  3. Consider the reaction Sn4+ + 2e → Sn2+

    The Sn4+ ion gains 2 electrons to form the Sn2+ ion.

    Sn4+ has been reduced because it has gained 2 electrons.

    The charge on tin has decreased from 4+ for Sn4+ to 2+ for Sn2+ .

    Tin has become more negative (less positive).


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