Ques. 1NEET (UG) 2023
On balancing the given redox reaction, a Cr2O72-(aq) + b SO32-(aq) + cH+(aq) 2a Cr3+(aq) + b SO42-(aq) + c2H2O( ) the coefficients a, b and c are found to be, respectively -
- 3, 8, 1
- 1, 8, 3
- 8, 1, 3
- 1, 3, 8
Answer
(4) 1, 3, 8
Solution
Cr goes from +6 +3, a gain of 3e- per Cr, i.e. 6e- per Cr2O72-, while S goes from +4 +6, a loss of 2e- per SO32-.
To balance the electrons, Cr2O72- : SO32- = 1 : 3, so a = 1 and b = 3.
Balancing the charge:
-2 - 6 + c = +6 - 6
c = 8 (and c2 = 4 H2O)
Hence the balanced equation is
Cr2O72- + 3SO32- + 8H+
2Cr3+ + 3SO42- + 4H2O
Answer: (4)