10 Questions
What is the advantage of using potassium permanganate in redox titrations?
It acts as its own indicator giving a clear colour change.
What is the purpose of adding dilute sulphuric acid to the ammonium iron (II) sulfate solution?
To prevent the iron (II) from reacting with the air to form iron (III)
What is the result of adding potassium permanganate to a solution of ammonium iron (II) sulfate in acidic conditions?
The manganese is reduced to Mn²⁺
Why is potassium permanganate not used as a primary standard?
It is not very stable and must be standardized against a primary standard.
What is the importance of using deionised water in the preparation of the ammonium iron (II) sulfate solution?
To prevent contamination of the solution
What is the oxidation state of manganese in potassium permanganate?
+7
What is the purpose of adding nitric acid to the potassium permanganate solution?
None of the above, nitric acid cannot be used for this purpose
What is the colour of the manganese in the +7 oxidation state?
Purple
Why is hydrochloric acid not used to prevent the formation of an intermediate oxidation state in potassium permanganate titrations?
It reacts with potassium permanganate
What is the result of the reaction between potassium permanganate and ammonium iron (II) sulfate in acidic conditions?
The complete reduction of manganese
Study Notes
Potassium Permanganate in Redox Titrations
- Potassium Permanganate (KMnO₄) is a useful oxidizing agent in redox titrations.
- It has the advantages of reacting completely and acting as its own indicator, giving a clear color change from purple to colorless.
Advantages and Disadvantages
- The advantages of KMnO₄ include its complete reaction and ability to act as its own indicator.
- The disadvantages include its instability and need for standardization against a standard solution of ammonium iron (II) sulfate prior to titration.
Standardization of Potassium Permanganate
- Ammonium iron (II) sulfate is used as a primary standard for standardizing potassium permanganate.
- The standard solution of ammonium iron (II) sulfate is prepared by weighing and diluting it in dilute sulfuric acid.
- The acid is added to prevent the iron (II) from reacting with air to form iron (III).
Preparation of Ammonium Iron (II) Sulfate Solution
- Weigh the required amount of ammonium iron (II) sulfate.
- Wash the powder into a beaker with dilute sulfuric acid.
- Stir well to dissolve.
- Pour the solution into a volumetric flask.
- Rinse the stirring rod and beaker with deionized water, adding the rinsings to the flask.
- Add water to the flask to bring the bottom of the meniscus to the mark.
Potassium Permanganate Characteristics
- Potassium Permanganate contains Mn in the +7 oxidation state, which is purple in color.
- In acidic conditions, Mn is reduced completely to the +2 oxidation state, resulting in a colorless solution.
- Without acidic conditions, an intermediate oxidation state of +4 is reached, resulting in a brown color.
Importance of Acidic Conditions
- Dilute sulfuric acid is added to the KMnO₄ solution to maintain acidic conditions.
- HCl cannot be used as it reacts with KMnO₄.
- Nitric acid cannot be used as it is a strong oxidizing agent itself.
- A fresh solution of potassium permanganate must be prepared just before titrating, as it reacts with both water and sunlight when in solution.
Learn about the advantages and disadvantages of using potassium permanganate as an oxidising agent in redox titrations. Discover its benefits and limitations in chemical analysis.
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