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Chapter 16 | Electrochemistry
In acidic solution, we can use or generate hydrogen ions (H+). Adding seven water molecules to the left side
provides the necessary oxygen; the “left over” hydrogen appears as 14 H+ on the right:
The left side of the equation has a total charge of [2 (+3) = +6], and the right side a total charge of [−2 + 14 (+1) = +12]. The difference is six; adding six electrons to the right side produces a mass- and charge- balanced oxidation half-reaction (in acidic solution):
Checking the half-reaction:
Now work on the reduction. It is necessary to convert the four oxygen atoms in the permanganate into four water molecules. To do this, add eight H+ to convert the oxygen into four water molecules:
Then add five electrons to the left side to balance the charge:
Make sure to check the half-reaction:
Collecting what we have so far:
The least common multiple for the electrons is 30, so multiply the oxidation half-reaction by five, the reduction half-reaction by six, combine, and simplify:
Checking each side of the equation:
This is the balanced equation in acidic solution.
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