Potassium permanganat is used as an
oxidizing agent to determine the hydrogen
peroxide amount in a solution. Hydrogen peroxide
reduces the permanganate to a colorless product.
This is a great example for a redox reaction.
2 KMnO4 + 3
5H2O2 = 2 MnSO4
+ K2SO4 + 5O2 +
or less confusing
5 H2O2 +
2MnO4- + 6H+ =
5O2 + 2Mn2+ +
Manganese can exist in all oxidation
states from +2 to +7. Manganese II forms salts
with all common anions. They are mostly
light pink in color. Manganese VII is found in the
intense purple colored permanganate ions
MnO4-. As long as you have
hydrogen peroxide in your solution, the
permanganate will always be reduced to a clear
solution. But as soon as the hydrogen peroxide is
gone the intense purple color of the permanganate
will be visible.
Note: It is important that the hydrogen
peroxide solution is acidic. The hydrogen ions
take part in the reaction as a reactant. The
protons are needed to form water. It is also
important to use sulfuric acid and not
hydrochloric acid because the permanganate is such
a powerful oxidant, it would oxidize chloride ions
to form chlorine.
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