Combining Half Equations
Redox Worksheet
Write Half Equations & Combine
1.
Sodium reducing aluminium ions to aluminium.
Oxidation
Na
→
Na+ + e– (x3)
Reduction
Al3+ + 3e–
→
Al
Overall Equation
3Na + Al3+
→
3Na+ + Al
2.
Oxidation of iron(II) to iron(III) using manganate(VII). Manganate(VII) is reduced to Manganese(II) in the reaction.
Oxidation
Fe2+
→
Fe3+ + e– (x5)
Reduction
MnO4– + 8H+ + 5e–
→
Mn2+ + 4H2O
Overall Equation
MnO4– + 8H+ + 5Fe2+
→
Mn2+ + 4H2O + 5Fe3+
3.
Reduction of dichromate(VII) to chromium(III) by Hydrogen peroxide. Hydrogen peroxide is oxidised to produce hydrogen ions and oxygen.
Reduction
Cr2O72- + 14H+ + 6e–
→
2Cr3+ + 7H2O
Oxidation
H2O2
→
2H+ + O2 + 2e– (x3)
Overall Equation
Cr2O72- + 8H+ + 3H2O2
→
2Cr3+ + 7H2O + 3O2
4.
Reduction of sulfate(VI) ions to sulfur dioxide using bromide. Bromide is oxidised in the process.
Reduction
SO42- + 4H+ + 2e–
→
SO2 + 2H2O
Oxidation
2Br–
→
Br2 + 2e–
Overall Equation
SO42- + 4H+ + 2Br–
→
SO2 + 2H2O + Br2
5.
Reduction of hydrogen by potassium.
Reduction
H2 + 2e–
→
2H–
Oxidation
K
→
K+ + e– (x2)
Overall Equation
H2 + 2K
→
2KH
6.
Oxidation of tin(II) to tin(IV) by ClO3–. ClO3– is reduced to its lowest possible oxidation state.
Oxidation
Sn2+
→
Sn4+ + 2e– (x3)
Reduction
ClO3– + 6H+ + 6e–
→
Cl– + 3H2O
Overall Equation
ClO3– + 6H+ + 3Sn2+
→
Cl– + 3H2O + 3Sn4+
7.
Oxidation of I– to I2 using dichromate(VII). Dichromate(VII) is reduced to form Cr3+.
Reduction
Cr2O72- + 14H+ + 6e–
→
2Cr3+ + 7H2O
Oxidation
2I–
→
I2 + 2e– (x3)
Overall Equation
Cr2O72- + 14H+ + 6I–
→
2Cr3+ + 7H2O + 3I2
8.
Oxidation of ethanedioate to carbon dioxide using manganate(VII).
Oxidation
C2O42-
→
2CO2 + 2e– (x5)
Reduction
MnO4– + 8H+ + 5e–
→
Mn2+ + 4H2O (x2)
Overall Equation
2MnO4– + 16H+ + 5C2O42-
→
2Mn2+ + 8H2O + 10CO2
9.
KNO2 is completely oxidised by potassium manganate(VII).
Oxidation
NO2– + H2O
→
NO3– + 2H+ + 2e– (x5)
Reduction
MnO4– + 8H+ + 5e–
→
Mn2+ + 4H2O (x2)
Overall Equation
2MnO4– + 6H+ + 5NO2–
→
2Mn2+ + 3H2O + 5NO3–