Redox titrations: MCQ 4

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.