Preparation and Standardization of Potassium Permanganate Standard Solution Purposes
Experiment 5
Preparation and Standardization of
Potassium Permanganate Standard Solution
Purposes
1.To know the method of preparation and standardization of potassium permanganate standard solution.
2. To grasp the principle, the conditions and the method of permanganate titration.
3. To grasp the determination of hydrogen peroxide in hydrogen peroxide solution with permanganate method.
Principle
Permanganate titration with potassium permanganate solution (KMnO4) as standard solution is one of the oxidation-reduction titration methods. KMnO4 is a vigorous oxidant in an acidic solution, and its electrode reaction and standard electrode potential φ are as follows,
MnO4- + 8H+
Mn2+ + 4H2O φ = + l.51V
The contents of many reducible substances can be determined directly or indirectly by the permanganate method.
The titration reaction of permanganate method should be carried out in sulfuric acid
(H2SO4) solution. Because nitric acid (HNO3) is of oxidization, and because hydrochloric acid (HCl) is of reduction, they are unavailable to adjust the acidic concentration of solution. In general, the available concentration of H2SO4 is
1
c( H2SO4)=1~2molL-l. If the acidic concentration is too high, it will result in
2
decomposition of KMnO4:
4MnO4- + 12H+
4Mn2+ + 5O2
+ 6H2O
If it is too low, the reduction product of KMnO4 is MnO2 which is brown deposit, and this kind of reaction can not be used in titration reaction, either.
KMnO4 on sale usually contains impurities such as manganese dioxide, chloride, sulfate, nitrate and so on. Therefore, it can not be used directly in the preparation of standard solution. Moreover, because the oxidization ability of KMnO4 is strong, and it readily reacts with reductive substances such as organic impurities in water, ashes in air and so on, it easily decomposes when exposed to light. When it is prepared, its solution must be boiled or be dissolved with cold distilled water and then kept in brown reagent bottle in dark.
The primary standard
Preparation and Standardization of
Potassium Permanganate Standard Solution
Purposes
1.To know the method of preparation and standardization of potassium permanganate standard solution.
2. To grasp the principle, the conditions and the method of permanganate titration.
3. To grasp the determination of hydrogen peroxide in hydrogen peroxide solution with permanganate method.
Principle
Permanganate titration with potassium permanganate solution (KMnO4) as standard solution is one of the oxidation-reduction titration methods. KMnO4 is a vigorous oxidant in an acidic solution, and its electrode reaction and standard electrode potential φ are as follows,
MnO4- + 8H+
Mn2+ + 4H2O φ = + l.51V
The contents of many reducible substances can be determined directly or indirectly by the permanganate method.
The titration reaction of permanganate method should be carried out in sulfuric acid
(H2SO4) solution. Because nitric acid (HNO3) is of oxidization, and because hydrochloric acid (HCl) is of reduction, they are unavailable to adjust the acidic concentration of solution. In general, the available concentration of H2SO4 is
1
c( H2SO4)=1~2molL-l. If the acidic concentration is too high, it will result in
2
decomposition of KMnO4:
4MnO4- + 12H+
4Mn2+ + 5O2
+ 6H2O
If it is too low, the reduction product of KMnO4 is MnO2 which is brown deposit, and this kind of reaction can not be used in titration reaction, either.
KMnO4 on sale usually contains impurities such as manganese dioxide, chloride, sulfate, nitrate and so on. Therefore, it can not be used directly in the preparation of standard solution. Moreover, because the oxidization ability of KMnO4 is strong, and it readily reacts with reductive substances such as organic impurities in water, ashes in air and so on, it easily decomposes when exposed to light. When it is prepared, its solution must be boiled or be dissolved with cold distilled water and then kept in brown reagent bottle in dark.
The primary standard