Question

Balance Fe²⁺ + Cr₂O₇^2- → Fe³⁺ + Cr³⁺ is acid media.

Answer 1

Step-1:

(LEO = Loss of Electron Oxidation)

(GER = Gain of Electron Reduction)

Step-2: Fe²⁺ → Fe³⁺ … (1) 

(2 → 3 = 1 unit ON),

Cr₂O₇^2- → 2Cr³⁺ … (2) 

(+6 → +3 = 3 units 2 sets ⇒ 6 units ON)

Step-3: Cross multiplication i.e., (1) x 6 and (2) x 1

(1) x 6 ⇒ 6Fe²⁺ → 6Fe³⁺ … (3)

(2) x 1 ⇒ Cr₂O₇^2- → 2Cr³⁺ …(4)

Step-4: Add (3) + (4) 

⇒ 6Fe²⁺ + Cr₂O₇^2- → 6Fe³⁺ + 2Cr³⁺

Step-5: Balance Oxygen and then Hydrogen

6Fe²⁺ + Cr₂O₇^2- + 14H⁺ → 6Fe³⁺ + 2Cr³⁺ + 7H₂O