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28. DRAWING UP EQUATIONS OF OXIDATION REDUCTION REACTIONS.
There are two methods of drawing up okislitelno - recovery reactions - method of electronic balance and method of semi-reactions. Here we will consider method of electronic balance.
In this method compare oxidation levels of atoms in mother substances and in reaction products, priety we are guided by the rule: the number of the electrons given by reducer has to equal to number of the electrons attached by oxidizer.
For drawing up the equation it is necessary to know formulas of reactants and reaction products. Let's consider this method on example.
To place coefficients in reaction which scheme:
HCl + MnO2 Cl2+ MnCl2 + H2O
Algorithm of arrangement of coefficients 1. We specify oxidation levels of chemical elements.
Chemical elements in which oxidation levels have changed are emphasized.
2. We work out the electronic equations in which we specify number of the given and accepted electrons.
Behind vertical line we put number of the electrons which have passed at oxidizing and recovery processes. We find least common multiple (it is taken in red circle). We divide this number into number of the moved electrons and we receive coefficients (are taken in blue circle). Means manganese will be faced by coefficient-1 which we do not write, and before Cl2-1 too.
Before HCl 2 we do not put coefficient, and we consider number of chlorine atoms in reaction products. It is equal - 4. Therefore and before HCl we put - 4, we equalize number of hydrogen atoms and oxygen on the right, having delivered before H2O coefficient - 2. As a result chemical equation will turn out:
Let's consider more difficult equation: H2S + KMnO4 + H2SO4 S We place oxidation levels of chemical elements:
The electronic equations will take the following form
Before sulfur with oxidation levels-2 and 0 we put coefficient 5, before compounds of manganese-2, we equalize number of atoms of other chemical elements and we receive the final equation of reaction
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