balancing redox reactions occured in the basic solution : Cl2 + SO2(g) --> Cl^- (aq) + SO4^-2(aq)
To balance a redox reaction that occurs in a basic solution, follow these steps:
Step 1: Divide the reaction into two half-reactions, one for oxidation and one for reduction.
For the reaction: Cl2 + SO2(g) -> Cl^-(aq) + SO4^-(2-)(aq)
The oxidation half-reaction is: Cl2 -> Cl^-
The reduction half-reaction is: SO2(g) -> SO4^-(2-)
Step 2: Balance atoms other than oxygen and hydrogen in each half-reaction.
In the oxidation half-reaction: Cl2 -> 2Cl^-
In the reduction half-reaction: SO2(g) -> SO4^-(2-)
Step 3: Balance oxygen atoms by adding water molecules to the side that requires more oxygen atoms.
Since there are no oxygen atoms on either side of the half-reactions, we can move to the next step.
Step 4: Balance hydrogen atoms by adding hydrogen ions (H+) to the side that requires more hydrogen atoms.
In the oxidation half-reaction: Cl2 + 2e- -> 2Cl^-
In the reduction half-reaction: SO2(g) + 2H2O -> SO4^-(2-) + 4H+
Step 5: Balance the charges in each half-reaction by adding electrons (e-).
In the oxidation half-reaction: Cl2 + 2e- -> 2Cl^-
In the reduction half-reaction: SO2(g) + 2H2O -> SO4^-(2-) + 4H+ + 2e-
Step 6: Make the number of electrons equal in both half-reactions by multiplying the equations by appropriate coefficients.
In this case, we need to multiply the oxidation half-reaction by 2 to balance the number of electrons.
2Cl2 + 4e- -> 4Cl^-
Step 7: Combine the half-reactions and cancel out common terms.
2Cl2 + 4e- + SO2(g) + 2H2O -> 4Cl^- + SO4^-(2-) + 4H+ + 2e-
Step 8: Simplify the equation and cancel out the electrons.
2Cl2 + SO2(g) + 2H2O -> 4Cl^- + SO4^-(2-) + 4H+
Lastly, make sure to check that the charges and atoms are balanced on both sides of the equation. In the case of this balanced equation, the number of atoms and charges are equal on both sides.
I don't know how to do this without ending up balancing the equation and you need to learn how to do it yourself. Here is a site that explains all about redox equations. Post back here for specific questions. You need to know the change in oxidation state; for S it is from +4 to +6. For Cl it is from zero to -1(each).
http://www.chemteam.info/Redox/Redox.html