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Oxidation : any process by which an entity loses electrons.

Oxidation : any process by which an entity loses electrons. e.g. 2Mg o + O 2 o 2Mg 2+ + O 2- H 2 o + F 2 o 2H + F - Mg and H are oxidised in these examples. Reduction : any process by which an entity gains electrons. Oxygen and fluorine are reduced in the above examples.

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Oxidation : any process by which an entity loses electrons.

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  1. Oxidation: any process by which an entity loses electrons. • e.g. 2Mgo + O2o 2Mg2+ + O2- • H2o + F2o 2H+F- • Mg and H are oxidised in these examples. • Reduction: any process by which an entity gains electrons. • Oxygen and fluorine are reduced in the above examples. • Nomenclature: positive ions are called “ cations” • negative ions are called “ anions” • Oxidation state: the sign and magnitude of the charge on • an ion (also called oxidation number).

  2. Note: 1. Oxidation state of an element in the uncombined state always equal to zero. 2. The algebraic sum of the oxidation states of all the atoms in the molecular formula of a compound is zero. 3. In complex ions (contain more than one atom) the sum of the oxidation states of all the constituents must equal overall charge on the ion. Common Oxidation States of Elements 1. Hydrogen usually +1. 2. Oxygen usually -2. 3. Halogens (i.e. F, Cl, Br, I) usually -1. 4. Metal ions are invariably positive.

  3. Example: Calculate the oxidation state of S in the S2O32- ion. • Solution: • Oxidation state of oxygen is -2. • Sum of oxidation states of all the elements in the ion must • equal the charge on the ion. • \ 2 (ox. st. of S) + 3 (-2) = -2 • 2 (ox. st. of S) - 6 = -2 • 2 (ox. st. of S) = +4 • \oxidation state of S = +2

  4. Example: Calculate the oxidation state of S in the S2O82- ion. • Solution: Oxidation state of oxygen is -2. • 2 (ox. st. of S) + 8 (-2) = - 2 • 2 (ox. st. of S) - 16 = - 2 • 2 (ox. st. of S) = + 14 • \oxidation state of S = +7 • Example: Calculate the oxidation state of Mn in KMnO4. • Solution: Oxidation state of oxygen is -2. • 1 +ox. st. of Mn + 4 (-2) = 0 • 1+ ox. st. of Mn - 8 = 0 • ox. st. of Mn = + 7 • \oxidation state of Mn = +7

  5. Nomenclature of Cations • CationName • Al3+ Aluminium • Ba2+ Barium • Na+ Sodium • Cu+ Cuprous or copper (I) • Cu2+ Cupric or copper (II) • Fe2+ Ferrous • Fe3+ Ferric • Sn2+ Stannous • Sn4+ Stannic • NH4+ Ammonium

  6. Nomenclature of Anions • AnionName • Br- Bromide • Cl- Chloride • O2- Oxide • S2- Sulphide • OH- Hydroxide • NO3- Nitrate • CO32- Carbonate • SO42- Sulphate • PO43- Phosphate • CN- Cyanide

  7. Oxidation States of Some Common Ions Cations Anions +1 +2 +3 +4 -1 -2 -3 Li+ Be2+ Al3+ Si4+ F- O2- N3- Na+ Mg2+ Sc3+ Mn4+ Cl- S2- P3- K+ Ca2+ Y3+ U4+ Br- Se2- Rb+ Sr2+ Ga3+ Th4+ I- CO32- Cs+ Ba2+ Sb3+ Ce4+ OH- SO42- Cu+ Mn2+ Bi3+ NO3- Ag+Fe2+ V3+ NO2- Tl+ Co2+ Cr3+ CN- H+ Ni2+Fe3+ MnO4- NH4+ Cu2+ Co3+ Zn2+ Cd2+

  8. Oxidation and Reduction - Summary • Oxidation = loss of electrons • Reduction = gain of electrons • Oxidation state or number: sign and magnitude of • charge on ion • Hydrogen +1; oxygen -2; halides usually -1; metals • usually +ve. • Calculation of oxidation states in ions and molecules

  9. Photography • light • 2 AgBr 2Ag + Br2 light, hn

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