Question

Cr2O72- + S(s) = Cr3+ + SO32-

Answer 1

Step 1: Separate the skeleton equation into two half-reactions.

Cr2O2-7→Cr3+

SO2-3→SO2-4

Step 2: Balance all atoms other than H and O.

Cr2O2-7→2Cr3+

SO2-3→SO2-4

Step 3: Balance O.

Add enough H2O molecules to balance O.

Cr2O2-7→2Cr3++7H2O

SO2-3+H2O→SO2-4

Step 4: Balance H.

Add enough H+ ions to balance H.

Cr2O2-7+14H+→2Cr3++7H2O

SO2-3+H2O→SO2-4+2H+

Step 5: Balance charge.

Add electrons to the side that needs more negative charge.