1. Balancing Half-Reactions in Basic Solution
Example 1
Here, we’ll go through an example of balancing a half-reaction in basic solution.

2. Balance the half-reaction:
(basic solution)
We’re asked to balance the half-reaction: H2AlO3 minus gives Al, taking place in basic solution.

3. Balance the half-reaction: (basic solution)
We’ll start by adding H2AlO3 minus to the left side

4. Balance the half-reaction: (basic solution)
And Al to the right side.

5. Balance in Acid Solution
Balance the half-reaction: (basic solution)
Even when we’re balancing a half-reaction in basic solution, we still start with the steps for acid solution. We begin by balancing atoms other than hydrogen or oxygen.

6. Balance Aluminum Atoms1 1
Balance the half-reaction: (basic solution)
In this case the element is aluminum.

7. Balance Aluminum Atoms1 1
Balance the half-reaction: (basic solution)
We have one Al on each side, so aluminum atoms are already balanced.

8. Balance Oxygen Atoms Balance the half-reaction: (basic solution)
The next step is to balance oxygen atoms.

9. Balance Oxygen Atoms 3 Balance the half-reaction: (basic solution)
Notice we have 3 oxygen atoms on the left side. Remember we balance oxygen atoms by adding a water molecule on the right for every excess oxygen atom on the left.

10. Balance Oxygen Atoms 3 Balance the half-reaction: (basic solution)
So we add 3 water molecules to the right side.

11. Balance Oxygen Atoms 3 3 Balance the half-reaction: (basic solution)
Now we have 3 oxygen atoms on both sides, so oxygen is balanced.

12. Balance Hydrogen Atoms
Balance the half-reaction: (basic solution)
The next step is to balance hydrogen atoms.

13. Balance Hydrogen Atoms2 6
Balance the half-reaction: (basic solution)
At this point we have 2 hydrogens on the left and 6 hydrogens on the right.

14. Balance Hydrogen Atoms We need to add 4 H’s to the left side2 6
We need to add 4 H’s to the left side
Balance the half-reaction: (basic solution)
In order to get 6 hydrogens on the left, we need to (click) add 4 hydrogens to the left side.

15. Balance Hydrogen Atoms2 6
add 4 H+ to the left side
Balance the half-reaction: (basic solution)
We do this by (click) adding 4 H+ ions to the left side

16. Balance Hydrogen Atoms2 4 6
Balance the half-reaction: (basic solution)
So on the left side, we now have a total of 2 plus 4

17. Balance Hydrogen Atoms2 4 6 6
Balance the half-reaction: (basic solution)
Which is equal to 6 hydrogens

18. Balance Hydrogen Atoms2 4 6 6
Balance the half-reaction: (basic solution)
And we have 6 hydrogens on both sides, so hydrogen is balanced.

19. Balance Charge Balance the half-reaction: (basic solution)
The next step is to balance the charge.

20. Balance Charge –1 +4 Balance the half-reaction: (basic solution)
Looking on the left side, we see that H2AlO3 minus has an ionic charge of negative 1 and 4H+ has a total ionic charge of positive 4.

21. Balance Charge –1 +4 Balance the half-reaction: (basic solution)
So the total ionic charge on the left side is —1 + positive 4,

22. Balance Charge –1 +4 +3 Balance the half-reaction: (basic solution)
Which equals positive 3

23. Balance Charge –1 +4 +3 Balance the half-reaction: (basic solution)+3
Balance the half-reaction: (basic solution)
And on the right side, the total charge is 0 plus 0

24. Balance Charge –1 +4 +3 Balance the half-reaction: (basic solution)+3
Balance the half-reaction: (basic solution)
Which equals zero

25. Add 6 e– to the more positive side
Balance Charge
Add 6 e– to the more positive side +3
Balance the half-reaction: (basic solution)
In order to balance charge, we must add enough electrons to the more positive side, to make the charges equal

26. Add 3 e– to the more positive side
Balance Charge
Add 3 e– to the more positive side +3
Balance the half-reaction: (basic solution)
Because the charge on the left side is +3 and the charge on the right side is zero, we must add (click) 3 electrons to the left side.

27. Balance Charge Add 3 e– to the Left side +3
Balance the half-reaction: (basic solution)
So we add 3 electrons to the left side.

28. Balance Charge –1 +4 –3 Balance the half-reaction: (basic solution)
Balance the half-reaction: (basic solution)
And now the total ionic charge on the left side is –1 plus positive 4 plus – 3

29. Balance Charge –1 +4 –3 Balance the half-reaction: (basic solution)
Balance the half-reaction: (basic solution)
Which is equal to zero

30. Balance Charge –1 +4 –3 Balance the half-reaction: (basic solution)
Balance the half-reaction: (basic solution)
So the total charge on the left is equal to the total charge on the right, and charge is balanced.

31. Balanced in Acid Solution Balanced in Acid Solution
Balance the half-reaction: (basic solution)
This half-reaction is now balanced in Acid Solution

32. Balance in Basic Solution
Balance the half-reaction: (basic solution)
But the question asks us to balance this in Basic Solution.

33. Balance in Basic Solution
We must get rid of the 4H+
Balance the half-reaction: (basic solution)
For basic solution, we must get rid of the 4 H+. Equations in basic solution cannot have H+ ions in them.

34. To Change to Basic Solution
Add or
Balance the half-reaction: (basic solution)
In order to change an equation from acid solution to basic solution, we add either this equation, showing water forming H+ and OH minus,

35. To Change to Basic Solution
Add or
Balance the half-reaction: (basic solution)
Or it’s reverse, showing H+ and OH minus forming water. We use whichever equation we need to cancel H+ ions out of our equation in acid solution.

36. To Change to Basic Solution
Add or
n = the number of H+ ions we need to cancel
Balance the half-reaction: (basic solution)
n stands for the number of H+ ions that need to be cancelled.

37. Balance in Basic Solution We must cancel out 4H+ on the left side
Balance the half-reaction: (basic solution)
Going back to our equation in acid solution, we must cancel out the 4H+ ions on the left side of the equation. So we need to add an equation with 4H+ ions on the RIGHT

38. Balance in Basic Solution
Balance the half-reaction: (basic solution)
So we add this reaction with water on the left and H+ and OH minus on the right.

39. Balance in Basic Solution
Balance the half-reaction: (basic solution)
Because we need to cancel 4 H+ ions,

40. Balance in Basic Solution
Balance the half-reaction: (basic solution)
n must be equal to 4

41. Balance in Basic Solution
Balance the half-reaction: (basic solution)
So 4 is the coefficient we use for all three species in this equation. Make sure they all have the same coefficient!

42. Balance in Basic Solution
Balance the half-reaction: (basic solution)
When we add these two equations together, (click) we see the 4H+ are on opposite sides, so they can be cancelled.

43. Balance in Basic Solution
Balance the half-reaction: (basic solution)
So we’ll cancel them and we’re left with this.

44. Balance in Basic Solution
Balance the half-reaction: (basic solution)
Notice we now have (click) 4H2O on the left side, and 3 H2O on the right side.

45. Balance in Basic Solution
Remove 3H2O from
BOTH SIDES
Balance the half-reaction: (basic solution)
We can do something to an equation as long as we do the same thing to BOTH sides. So we can (click) remove 3 H2O molecules from both sides. This is called simplifying the equation.

46. Balance in Basic Solution
Remove 3H2O from
BOTH SIDES
Balance the half-reaction: (basic solution)
This leaves us with no H2O on the right side of the top equation.

47. Balance in Basic Solution1
Remove 3H2O from
BOTH SIDES
Balance the half-reaction: (basic solution)
And 4 minus 3 equals 1 water on the left of the lower equation.

48. Balance in Basic Solution1
Balance the half-reaction: (basic solution)
We’ll remove the coefficient 1 because we don’t need it.

49. Balance in Basic Solution
Balance the half-reaction: (basic solution)
Now we add what’s left of these two equations, to get our final equation. We’ll start by adding everything on the (click) left side of the arrows. We have 1 (click) H2AlO3 minus

50. Balance in Basic Solution
Balance the half-reaction: (basic solution)
One H2O,

51. Balance in Basic Solution
Balance the half-reaction: (basic solution)
And 3 electrons on the left side. Now we’ll add what we have on the right side

52. Balance in Basic Solution
Balance the half-reaction: (basic solution)
On the right side, we have 1 Al

53. Balance in Basic Solution
Balance the half-reaction: (basic solution)
And 4 OH minus

54. Balance in Basic Solution Balanced Half-reaction in BASIC Solution
Balance the half-reaction: (basic solution)
So now we have our finished balanced half-reaction in basic solution.

55. Balanced Half-reaction in Basic Solution
CHECK
Balance the half-reaction: (basic solution)
What we should do now is (click) check this to make sure atoms and charge are balanced.

56. Balanced Half-reaction in Basic Solution
4 H’s
Balance the half-reaction: (basic solution)
We see we have a total of 2 + 2, which equals 4 H’s on the left side,

57. Balanced Half-reaction in Basic Solution
4 H’s
4 H’s
Balance the half-reaction: (basic solution)
And 4 H’s on the right side. So Hydrogen atoms are balanced.

58. Balanced Half-reaction in Basic Solution
Balance the half-reaction: (basic solution)
We have 1 Al on both sides, so aluminum atoms are balanced.

59. Balanced Half-reaction in Basic Solution
4 O’s
Balance the half-reaction: (basic solution)
We have a total of 3 plus 1, which is 4 O’s on the left side

60. Balanced Half-reaction in Basic Solution
4 O’s
4 O’s
Balance the half-reaction: (basic solution)
And 4 O’s on the right side, so oxygen atoms are balanced.

61. Balanced Half-reaction in Basic Solution–1 –3
Balance the half-reaction: (basic solution)
Now we’ll check the charge. We have a total of negative negative 3 on the left side,

62. Balanced Half-reaction in Basic Solution–1 –3 –4
Balance the half-reaction: (basic solution)
Negative 1, 0 and negative 3 add up to negative 4, which is the total ionic charge on the left side.

63. Balanced Half-reaction in Basic Solution–1 –3 –4 –4
Balance the half-reaction: (basic solution)
On the right side we have 4 times negative 1, which equals (click) negative 4.

64. Balanced Half-reaction in Basic Solution–1 –3 –4 –4
Balance the half-reaction: (basic solution)
So charge is balanced.

65. Balanced Half-reaction in Basic Solution
Balance the half-reaction: (basic solution)
And this is the balanced half-reaction for H2AlO3 minus forming Al in basic solution.