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Give the rules for the calculation of oxidation number. |
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Answer» Solution :In elements, in the FREE or the uncombined state, each atom bears an oxidation number of zero. E.g., `H_(2),O_(2),Cl_(2),N_(2),Na,Mg,Al,S_(8),P_(4)` has oxidation number zero. For ions composed of only atom, the oxidation number is equal to the charge on the ION. `Na^(+)` ion has an oxidation number = +1 `Mg^(+2)` ion has an oxidation number = +2 `Al^(+3)` ion has an oxidation number = +3 `Cl^(-)` ion has an oxidation number = -1 `O^(-2)` ion has an oxidation number = -2 `F^(-)` ion has an oxidation number = -1 Compounds of all alkali metals have +1 oxidation number and all alkaline earth metals have oxidation number +2. e.g., `Na^(+),K^(+),CS^(+),Rb^(+),Li^(+)andMg^(+2),Ca^(+2),Be^(+2),Sr^(+2)` The oxidation number of OXYGEN in most compounds is -2. e.g., `H_(2)OtoO^(-2)" ",CuOtoO^(-2)` Exception : While in peroxide compounds each oxygen atom is assigned an oxidation number of -1. e.g., `H_(2)O_(2)toO^(-1),Na_(2)O_(2)toO^(-1),BaO_(2)toO^(-1)` Oxidation number of oxygen in superoxide compounds is `-1/2`. e.g., `KO_(2)toO^(-1/2)" ",RbO_(2)toO^(-1/2)` When oxygen is bonded to fluorine, the oxidation number of oxygen is +2 and +1. e.g., `OF_(2)toO^(+2)" ",O_(2)F_(2)toO^(+1)` The oxidation number of hydrogen is +1. When it bonded to metals, in binary compounds its oxidation number is -1. e.g., `LiHtoH^(-1)" ",NaHtoH^(-1)" ",CaH_(2)toH^(-1)` In all its compounds, fluorine has oxidation number of -1. Other halogens (Cl, Br, I) also have an oxidation number of -1. Halogens combined with oxygen for in oxoacids and oxoanions has POSITIVE oxidation numbers. e.g., : `HCl toCl^(+1)" ",HClO_(2)toCl^(+3)` `HClO_(3)toCl^(+5)" ",HClO_(4)toCl^(+7)` `Cl_(2)O_(7)toCl^(+7)" ",Cl_(2)O_(3)toCl^(+3)` The algebraic sum of the oxidation number of all the atoms in a COMPOUND must be zero. In polyatomic ion the algebraic sum of all the oxidation number of atoms of the ion must equal the charge on the ion. Thus, the sum of oxidation number of three oxygen atoms and one carbon atom is the carbonate ion `(CO_(3))^(-2)` must equal -2. |
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