Balance redox reaction through oxidation method of an acid
Cr2O7- + Cl- --> Cr3+ + Cl2
Step 1: Write the unbalanced half-reactions for oxidation and reduction
Oxidation: Cr2O7- --> Cr3+
Reduction: Cl- --> Cl2
Step 2: Balance the number of atoms for the half-reactions except for H and O
Oxidation: Cr2O7- --> 2Cr3+
Reduction: 2Cl- --> Cl2
Step 3: Balance the number of oxygen atoms by adding H2O to the half-reaction that needs it
Oxidation: Cr2O7- + 14H+ --> 2Cr3+ + 7H2O
Reduction: 2Cl- --> Cl2
Step 4: Balance the number of hydrogen atoms by adding H+ to the other half-reaction
Oxidation: Cr2O7- + 14H+ --> 2Cr3+ + 7H2O
Reduction: 2Cl- + 2H+ --> Cl2 + H2
Step 5: Balance the charges by adding electrons to the half-reactions
Oxidation: Cr2O7- + 14H+ + 6e- --> 2Cr3+ + 7H2O
Reduction: 2Cl- + 2H+ + 2e- --> Cl2 + H2
Step 6: Multiply the half-reactions by integers to make the number of electrons equal in both half-reactions
Oxidation: 6Cr2O7- + 42H+ + 18e- --> 12Cr3+ + 21H2O
Reduction: 21Cl- + 21H+ + 21e- --> 21Cl2 + 21H2
Step 7: Add the half-reactions together and cancel out the common species
6Cr2O7- + 42H+ + 18Cl- --> 12Cr3+ + 21H2O + 21Cl2
Step 8: Verify that the charges and atoms are balanced on both sides of the equation
The charges and atoms are balanced on both sides of the equation.
To balance the redox reaction using the oxidation method, follow these steps:
Step 1: Identify the change in oxidation states for each element in the reaction.
In this reaction, we can see that the oxidation state of Cr changes from +6 to +3, indicating a reduction, while the oxidation state of Cl changes from -1 to 0, indicating an oxidation.
Step 2: Write the half-reactions for oxidation and reduction.
Oxidation half-reaction: Cl- → Cl2
Reduction half-reaction: Cr2O7- → Cr3+
Step 3: Balance the atoms other than oxygen and hydrogen in each half-reaction.
Oxidation half-reaction: 2Cl- → Cl2
Reduction half-reaction: 2Cr2O7- → 2Cr3+
Step 4: Balance the oxygen atoms by adding water molecules.
Oxidation half-reaction: 2Cl- → Cl2 + 2e-
Reduction half-reaction: 2Cr2O7- + 14H+ → 2Cr3+ + 7H2O + 6e-
Step 5: Balance the hydrogen atoms by adding hydrogen ions (H+).
Oxidation half-reaction: 2Cl- + 2H+ → Cl2 + 2e-
Reduction half-reaction: 2Cr2O7- + 14H+ → 2Cr3+ + 7H2O + 6e-
Step 6: Balance the charge by multiplying the half-reactions by appropriate coefficients so that the electrons cancel out.
Oxidation half-reaction (multiplied by 6): 6Cl- + 6H+ → 3Cl2 + 6e-
Reduction half-reaction (multiplied by 2): 4Cr2O7- + 28H+ → 4Cr3+ + 14H2O + 12e-
Step 7: Add the two half-reactions together and cancel out common species.
2Cr2O7- + 14H+ + 6Cl- + 6H+ → 4Cr3+ + 7H2O + 3Cl2 + 6e-
Step 8: Simplify the equation and combine the remaining species.
2Cr2O7- + 14H+ + 6Cl- → 4Cr3+ + 7H2O + 3Cl2
And there you have it! The balanced redox equation using the oxidation method.