Redox equations are often long and difficult to balance by inspection. Luckily, electron transfers and oxidation numbers provide hints for balancing such equations. Balance the following equation:
K2CrO4 + Na2SO3 + HCl ---> KCl + Na2SO4 + CrCl3 + H20
To balance the given redox equation (K2CrO4 + Na2SO3 + HCl ---> KCl + Na2SO4 + CrCl3 + H2O), we need to follow a step-by-step approach:
Step 1: Identify the elements undergoing oxidation and reduction.
In this equation, chromium (Cr) is being reduced from a +6 oxidation state to +3, while sulfur (S) is being oxidized from a +4 oxidation state to +6.
Step 2: Split the equation into half-reactions.
There are two half-reactions involved: the reduction half-reaction and the oxidation half-reaction.
Reduction Half-Reaction:
Cr + 3e- → Cr3+
Oxidation Half-Reaction:
S4+ → S6+ + 2e-
Step 3: Balance the atoms in the half-reactions (except hydrogen and oxygen).
Reduction Half-Reaction:
2Cr + 6e- → 2Cr3+ (multiplied by 2)
Oxidation Half-Reaction:
S4+ → S6+ + 2e- (already balanced)
Step 4: Balance the charges in the half-reactions by adding the appropriate number of electrons.
Reduction Half-Reaction:
2Cr + 6e- → 2Cr3+ (already balanced)
Oxidation Half-Reaction:
S4+ + 2e- → S6+ + 2e- + 2e- (added 2 electrons to balance the charges)
Step 5: Combine the half-reactions by multiplying them by appropriate coefficients to make the number of electrons equal.
Reduction Half-Reaction (multiplied by 3):
6Cr + 18e- → 6Cr3+
Oxidation Half-Reaction (multiplied by 2):
2S4+ + 4e- → 2S6+ + 4e- + 4e-
Step 6: Add the half-reactions together and cancel out the electrons.
Final Balanced Equation:
6K2CrO4 + 2Na2SO3 + 36HCl → 6KCl + 3Na2SO4 + 6CrCl3 + 18H2O
After following these steps, we have successfully balanced the given equation (K2CrO4 + Na2SO3 + HCl ---> KCl + Na2SO4 + CrCl3 + H2O).
To balance the given redox equation:
1. Start by separating the equation into half-reactions. In this case, we will separate the equation into an oxidation half-reaction and a reduction half-reaction.
Oxidation half-reaction: K2CrO4 → CrCl3
Reduction half-reaction: Na2SO3 → Na2SO4
2. Balance the atoms in each half-reaction except for H and O.
Oxidation half-reaction: K2CrO4 → 2 KCl + CrCl3
Reduction half-reaction: Na2SO3 → Na2SO4 + H2O
3. Now balance the oxygen atoms by adding water (H2O) molecules to either side of the half-reactions as needed. One approach is to balance oxygen atoms first in the reduction half-reaction, as the oxidation half-reaction already has oxygen.
Oxidation half-reaction: K2CrO4 → 2 KCl + CrCl3
Reduction half-reaction: Na2SO3 + H2O → Na2SO4
4. Next, balance the hydrogen (H) atoms by adding H+ ions to the side of the equation that needs it. In this case, it is the oxidation half-reaction.
Oxidation half-reaction: K2CrO4 + 4 HCl → 2 KCl + CrCl3 + H2O
Reduction half-reaction: Na2SO3 + H2O → Na2SO4
5. Now balance the charge by adding electrons (e-) to the half-reactions. Add as many electrons as needed so that the total charge on each side is equal. The number of electrons needed depends on the change in oxidation state for each element.
Oxidation half-reaction: K2CrO4 + 4 HCl + 6 e- → 2 KCl + CrCl3 + H2O
Reduction half-reaction: Na2SO3 + H2O → Na2SO4 + 6 e-
6. Finally, multiply each half-reaction by the appropriate factor to ensure that the number of electrons is the same in both half-reactions. In this case, we will multiply the oxidation half-reaction by 6 and the reduction half-reaction by 1.
6 K2CrO4 + 24 HCl + 36 e- → 12 KCl + 6 CrCl3 + 6 H2O
6 Na2SO3 + 6 H2O → 6 Na2SO4 + 36 e-
7. Add the two balanced half-reactions together and cancel out any common terms.
6 K2CrO4 + 24 HCl + 36 e- + 6 Na2SO3 + 6 H2O → 12 KCl + 6 CrCl3 + 6 H2O + 6 Na2SO4 + 36 e-
8. Simplify the equation by canceling out common terms.
6 K2CrO4 + 24 HCl + 6 Na2SO3 → 12 KCl + 6 CrCl3 + 6 Na2SO4 + 6 H2O
And there you have it! The balanced redox equation.
I'll help you get started but I shall be happy to explain anything you don't understand.
Cr changes oxidation state from +6 on the left to +3 on the right.
S changes oxidation state from +4 on the left to +6 on the right.