Question

Balancing acid average equationa. PbO2 + Mn2+ -> Pb2+ + Mn04-

Answer 1

1) Balance the chemical equation.

`PbO_2+Mn^(2+)\rightarrow Pb^(2+)+MnO^-_4_{}`

Step 1: Assign oxidation numbers

PbO2: Pb (+4) and O (-2)

Mn2+: Mn (+2)

Pb2+: Pb (+2)

MnO4-: Mn (+7) and O (-2)

Step 2: Figure out what's being reduced and what's being oxidized.

Mn has been oxidized. It changed from (+2) to (+7)

Pb has been reduced. It changed from (+4) to (+2)

Step 3: Write half-reaction

Oxidation half-reaction

`Mn^(2+)\rightarrow MnO^-_4`

Reduction half-reaction

`PbO_2\rightarrow Pb^(2+)_{}`

Step 4: Balance all elements EXCEPT for hydrogen and oxygen

Oxidation half-reaction

`Mn^(2+)\rightarrow MnO^-_4`

Reduction half-reaction

`PbO_2\rightarrow Pb^(2+)_{}`

Step 5: Balance oxygens. We do so by adding water molecules to the half-reactions as needed.

Oxidation half-reaction

`Mn^(2+)+4H_2O\rightarrow MnO^-_4`

Reduction half-reaction

`PbO_2\rightarrow Pb^(2+)_{}+2H_2O`

Step 6: Balance hydrogens. We do so by adding protons (H+) to the half-reactions as needed.

Oxidation half-reaction

`Mn^(2+)+4H_2O\rightarrow MnO^-_4+8H^+`

Reduction half-reaction

`PbO_2+4H^+\rightarrow Pb^(2+)_{}+2H_2O`

Step 7: Balance charges. We do so by adding electrons

Oxidation half-reaction

`Mn^(2+)+4H_2O\rightarrow MnO^-_4+8H^++5e^-`

Reduction half-reaction

`PbO_2+4H^++2e^-\rightarrow Pb^(2+)_{}+2H_2O`

Step 8: Multiply half-reactions to make the number of electrons equal.

Oxidation half-reaction.

`2\cdot(Mn^(2+)+4H_2O\rightarrow MnO^-_4+8H^++5e^-)`

New oxidation half-reaction.

`2Mn^(2+)+8H_2O\rightarrow2MnO^-_4+16H^++10e^-`

Reduction half-reaction

`5\cdot(PbO_2+4H^++2e^-\rightarrow Pb^(2+)_{}+2H_2O)`

New reduction half-reaction

`5PbO_2+20H^++10e^-\rightarrow5Pb^(2+)_{}+10H_2O)`

Step 9: Cancel electrons and combine the half-reactions

Overall reaction

`2Mn^(2+)+8H_2O+5PbO_2+20H^+\rightarrow2MnO^-_4+16H^++5Pb^(2+)+10H_2O`

Step 10: Balance the chemical equation by reducing the number of water molecules and protons.

Overall reaction

`2Mn^(2+)+5PbO_2+4H^+\rightarrow2MnO^-_4+5Pb^(2+)+2H_2O`

2) The balanced chemical equation

Overall reaction

`2Mn^(2+)+5PbO_2+4H^+\rightarrow2MnO^-_4+5Pb^(2+)+2H_2O`

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