Question

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

Answer 1

Answer:

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

Explanation:

took the test

Answer 2

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.