To balance the given redox reaction involving the hydrogen sulfite ion (HSO3-) and iodate ion (IO3-) in an acidified solution, follow these steps:
Step 1: Identify the atoms and their oxidation states in the reactants and products.
Reactants: HSO3- and IO3-
Products: I2, SO4, H2O
Oxidation states:
HSO3-: Hydrogen has an oxidation state of +1, sulfur has an oxidation state of +4, and oxygen has an oxidation state of -2.
IO3-: Iodine has an oxidation state of +5, and oxygen has an oxidation state of -2.
I2: Iodine has an oxidation state of 0.
SO4: Sulfur has an oxidation state of +6, and oxygen has an oxidation state of -2.
H2O: Hydrogen has an oxidation state of +1, and oxygen has an oxidation state of -2.
Step 2: Determine the half-reactions for the oxidation and reduction processes.
Oxidation half-reaction:
In the reactants, hydrogen sulfite (HSO3-) has an oxidation state of +4, and in the products, sulfate (SO4) has an oxidation state of +6. Therefore, sulfur in hydrogen sulfite is being oxidized. The half-reaction for the oxidation is as follows:
5 HSO3- -> 5 SO4 + 10 H+ + 10 e-
Reduction half-reaction:
In the reactants, iodate (IO3-) has an oxidation state of +5, and in the products, iodine (I2) has an oxidation state of 0. Therefore, iodine in iodate is being reduced. The half-reaction for the reduction is as follows:
2 IO3- + 12 H+ + 10 e- -> I2 + 6 H2O
Step 3: Balance the charges by multiplying the half-reactions.
To balance the charges, we need to multiply the oxidation half-reaction by 2 and the reduction half-reaction by 5:
10 HSO3- -> 10 SO4 + 20 H+ + 20 e-
10 IO3- + 60 H+ + 50 e- -> 5 I2 + 30 H2O
Step 4: Balance the number of electrons in both half-reactions.
To balance the number of electrons, we need to multiply the oxidation half-reaction by 5 and the reduction half-reaction by 2:
50 HSO3- -> 50 SO4 + 100 H+ + 100 e-
20 IO3- + 120 H+ + 100 e- -> 10 I2 + 60 H2O
Step 5: Combine the two half-reactions.
Add the two balanced half-reactions together:
50 HSO3- + 20 IO3- + 120 H+ -> 50 SO4 + 10 I2 + 100 H2O
Step 6: Simplify the equation by canceling out common terms.
Simplify the equation by dividing all coefficients by 10:
5 HSO3- + 2 IO3- + 12 H+ -> 5 SO4 + I2 + 10 H2O
Thus, the balanced redox equation for the reaction involving hydrogen sulfite ion and iodate ion in an acidified solution is 5 HSO3- + 2 IO3- + 12 H+ -> 5 SO4 + I2 + 10 H2O.