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chlorate acid with chloride acid Chlorine with the oxidation state of +5 acts as an

oxidizer, and in the reaction of Berthollet’s salt decomposition under moderate the

heating acts as a reducing agent:

-1
0
+5
HCl O 3 + 5HCl = 3Cl 2 + 3H 2O oxidizing

+5 +7 -1
4KCl O 3 = 3KCl O 4+ KCl reducing

6.4 Equations of oxidative-reduction reactions

The atoms of Chromium and Chlorine have not changed their oxidation state. Let

us make up electronic equation with indices, which are located next to the elements

in the formulas:

0
–
2Cl - 2e = Cl 2 ,
+6
+3
2Cr + 6e = 2Cr .
Next, let us determine the coefficients for the oxidizer and reductant, given that the
amount of electrons that the reductant gives away is equal to the number of

electrons that the oxidant attaches. To do this let us find the least common
multiple (LCM) for the number of given and attached electrons. By dividing the

LCM by the number of electrons involved in the redox the coefficients for the
oxidizer and reducing agent are found:

– 0
2Cl - 2e = Cl 2 3
+6 +3
2Cr + 6e = 2Cr 1

The found coefficients are substituted in the equation of reaction:

K 2Cr 2O 7 + HCl → 2CrCl 3 + 3Cl 2 + KCl + H 2O.

In this equation, there is no coefficient before HCl, as a part of HCl is used to form

CrCl 3 and KCl. Next, let usequalize the number of metal ions, which have not

changed the oxidation state (potassium).

K 2Cr 2O 7 + HCl → 2CrCl 3 + 3Cl 2 + 2KCl + H 2O.

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