The chemical equation for a reaction between K2Cr2O7 and HCl is shown.

K2Cr2O7 + 14HCl → 2CrCl3 + 2KCl + 3Cl2 + 7H2O

Which of the following identifies the reactant that acts as an oxidizing agent in the reaction and explains the answer?

K2Cr2O7, because the oxidation number of K changes from + 6 to + 3.

K2Cr2O7, because the oxidation number of Cr changes from + 6 to + 3.

HCl, because the oxidation number of H changes from - 1 to 0.

HCl, because the oxidation number of Cl changes from - 1 to 0.

K2Cr2O7, because the oxidation number of Cr changes from + 6 to + 3.

Explanation:

took the test

K2Cr2O7 + 14HCl → 2CrCl3 + 2KCl + 3Cl2 + 7H2O

the correct option is:

K2Cr2O7, because the oxidation number of Cr changes from + 6 to + 3.

Oxidation number of Cr in K2Cr2O7 is:

K2Cr2O7 = 2K + 2 Cr + 7 O

= 2 (+1) + 2Cr + 7 (-2)

= 2 + 2Cr - 14

[total charge on K2Cr2O7 = 0], Hence;

2 + 2Cr - 14 = 0

2Cr - 12 = 0

2Cr = 12

Cr = 12/2

Cr = + 6

Oxidation number of Cr in CrCl3 is:

CrCl3 = Cr + 3Cl = 0

Cr + 3 (-1) = 0

Cr - 3 = 0

Cr = + 3

Hence Cr is changing its oxidation number from

+6 in K2Cr2O7 to + 3 in CrCl3.

Since the oxidation number of Cr [ + 6 → + 3] is decreasing here,

Cr is getting reduced.

so K2Cr2O7 is an oxidizing agent, as it is getting itself reduced and oxidizes others.