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Redox reaction in alkaline solution
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A redox reaction in alkaline solution is solved step by step.
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A complete step by step solution for working on a redox reaction in alkaline solutioTask: Complete the following redox reaction in alkaline solution:
-
MNQ
,
•
Mnoa AIOHI
Step 1: Determining oxidation numbers
Since aluminium is elementary, Al gets the oxidation number 0:
• -
Oxygen usually has the oxidation number -II, except in peroxides or O-F compounds. Since permanganate has four o
atoms, there is a total oxidation state of -VIII. Because permanganate has a single negative charge overall, the manga
must have an oxidation number of +VII:
•
:
M
'
Manganese dioxide has an overall neutral charge. Therefore, the sum of the oxidation numbers must be 0. The two ox
atoms have a total oxidation number of -lV. Thus, manganese must be +lV.
•
NO2 2
Hydrogen usually has the oxidation number +I, except in metal hydrids . Since hydroxide ions (OH ) have a single nega
charge, hydroxide ions have an oxidation number of -I. Since four hydroxide ions have the oxidation number -IV, Al mu
here, so that the sum of the oxidation Numbers is -I:
t)
• '
-
Step 2: Determining the oxidation and reduction reaction
Oxidation occurs when the oxidation number of an atom is increased. In this reaction, that is what happens to the alum
Since the oxidation number is increased by three, the aluminum loses three electrons:
IIOH
Bei
Oxidation: n
This reaction is not yet complete, because you still have to do a mass and charge balance. Since we are in an alkaline
environment, we can use hydroxide ions to balance. There are four hydroxide ions on the right side, so we also need fo
hydroxide ions on the left side. This also automatically balances the charges completely: there is a total charge of -4 on
and the same on the right.
Oxidation: -
. -
IOH 3. e-
Reduction occurs when the oxidation number of an atom decreases. Since the oxidation number of manganese decre
3, a reduction takes place here and manganese gains three electrons in the process:
Reduction: In 3. e- "
NO2
This reaction is also not yet complete. On the left side we have a fourfold negative charge. In order to balance this, we
four hydroxide ions on the right side. Now we still have to balance the atoms. On the right side there are a total of 6 ox
atoms and 4 hydrogen atoms. On the left side, however, there are only 4 oxygen atoms and no hydrogen atom. Since w
a solution, we can balance the equilibrium with water molecules. On the left side there are currently 2 oxygen atoms an
hydrogen atoms missing, so we need 2 water molecules:
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