Redox Reactions · Question 5

X and Y are the number of electrons involved, respectively during the oxidation of I- to I2 and S2- to S by acidified K2Cr2O7. The value of X + Y is .

Answer

12

Solution

In acidic medium, Cr2O72- + 14H+ + 6e- 2Cr3+ + 7H2O, so one dichromate ion accepts 6 electrons.

Oxidation of iodide:

Cr2O72- + 6I- + 14H+ 2Cr3+ + 3I2 + 7H2O

6 I- each lose 1 electron, X = 6

Oxidation of sulphide:

Cr2O72- + 3S2- + 14H+ 2Cr3+ + 3S + 7H2O

3 S2- each lose 2 electrons, Y = 6

X + Y = 6 + 6 = 12

Answer: 12