Question

balanced the equation bu oxidation number method and iron electron method ( half equation method) in basic medium .. 1) H2O2 + Cr2O2-7 -------- O2 + Cr3+.​

Answer 1

Explanation:

Cr2O72- <--> Cr3+ which becomes Cr2O72- <--> 2Cr3+ which becomes Cr2O72- <--> 2Cr3+ + 7H2O which becomes Cr2O72- +14H+ <--> 2Cr3+ + 7H2O which becomes Cr2O72- +14H+ +6e- <--> 2Cr3+ + 7H2O

Cr2O72- + 14H+ +6e- <--> 2Cr3+ + 7H2O (reduction)

(H2O2 <--> O2 + 2H+ + 2e-) x 3 (this is to balance the electrons

Cr2O72- + 14H+ + 6e- <--> 2Cr3+ + 7H2O and 3H2O2 <--> 3O2 + 6H+ + 6e-

Adding gives Cr2O72- + 14H+ + 6e- + 3H2O2 <--> 2Cr3+ + 7H2O + 3O2 + 6H+ + 6e- and simplifying gives

Cr2O72- + 8H+ + 3H2O2 <--> 2Cr3+ + 7H2O + 3O2

I think this is balanced