Balance the equation in acidic conditions. Phases are optional

Question

Cr2+ + H2MoO4 --> Cr3+ + Mo

Answer 1

I opt to omit phases for clarity.

Cr²⁺ ==>Cr³⁺ ... oxidation half reaction, unbalanced

Cr²⁺ ==>Cr³⁺ +e- .. balanced for Cr and charge = balanced oxidation reaction

H₂MoO₄ ==> Mo .. reduction reaction, unbalaned

H₂MoO₄ ==> Mo + 4H₂O.. balanced for Mo and O

H₂MoO₄ + 6H⁺ ==> Mo + 4H₂O .. balanced for Mo, O and H

H₂MoO₄ + 6H⁺ + 6e- ==> Mo + 4H₂O .. balanced for Mo, O, H and charge = balanced reduction rxn

Multiply oxidation rxn by 6 to balance electrons, then add the two reactions together:

6Cr²⁺ ==>6Cr³⁺ +6e-

H₂MoO₄ + 6H⁺ + 6e- ==> Mo + 4H₂O

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6Cr²⁺ + H₂MoO₄ + 6H⁺ + 6e- ==> 6Cr³⁺ +6e- + Mo + 4H₂O

6Cr²⁺ + H₂MoO₄ + 6H⁺ ==> 6Cr³⁺ + Mo + 4H₂O .. balanced redox in acid