How To Preparation and Standardization of 0.1N KMnO4 Solution?

Preparation and Standardization of 0.1N KMnO₄ Solution

Introduction

Potassium permanganate (KMnO₄) is a strong oxidizing agent used in redox titrations. Since it is not a primary standard, its solution must be standardized using oxalic acid (H₂C₂O₄·2H₂O) or sodium oxalate (Na₂C₂O₄).

Materials Required

Potassium permanganate (KMnO₄)
Oxalic acid dihydrate (H₂C₂O₄·2H₂O)
Sulfuric acid (H₂SO₄, 1N)
Distilled water
Volumetric flask (1L)
Burette (50mL)
Pipette (25mL)
Conical flask (250mL)
Hot plate

Preparation of 0.1N KMnO₄ Solution

Step 1: Calculate Required Amount

The equivalent weight of KMnO₄ in acidic medium (MnO₄^– → Mn²⁺) is:

Eq. wt. = Molar mass / 5 = 158.034 / 5 = 31.6068 g/equivalent

For 1L of 0.1N solution:

Required KMnO₄ = 0.1 × 31.6068 = 3.1607 g

Step 2: Solution Preparation

Weigh approximately 3.2-3.3g of KMnO₄ (to account for impurities)
Dissolve in 1L distilled water in a volumetric flask
Boil the solution for 15-30 minutes to destroy organic impurities
Cool and filter through glass wool to remove MnO₂
Store in an amber bottle

Standardization with Oxalic Acid

Step 1: Prepare 0.1N Oxalic Acid

Equivalent weight of oxalic acid dihydrate:

Eq. wt. = 126.07 / 2 = 63.035 g/equivalent

For 250mL of 0.1N solution:

Required oxalic acid = 0.1 × 63.035 × 0.25 = 1.5759 g

Step 2: Titration Procedure

Pipette 25mL of 0.1N oxalic acid into a conical flask
Add 20mL of 1N H₂SO₄
Heat the solution to 60-70°C
Titrate with KMnO₄ solution until a faint pink color persists for 30 seconds
Repeat for concordant readings

Step 3: Calculations

The redox reaction:

2MnO₄^– + 5C₂O₄^2- + 16H⁺ → 2Mn²⁺ + 10CO₂ + 8H₂O

Normality calculation:

N_KMnO4 = (N_Oxalic × V_Oxalic) / V_KMnO4

Burette Reading (mL)	Initial	Final	Used
Trial 1	0.00	24.50	24.50
Trial 2	0.00	24.40	24.40

Example calculation:

N = (0.1 × 25) / 24.5 = 0.102N

Precautions

Always perform titration in H₂SO₄ medium (HCl interferes due to Cl^– oxidation)
Maintain temperature between 60-70°C during titration
The first permanent pink color indicates the endpoint (excess MnO₄^–)
Filter the KMnO₄ solution to remove MnO₂ precipitates
Store in amber bottles as KMnO₄ is light-sensitive

Conclusion

The standardized 0.1N KMnO₄ solution can now be used for various redox titrations including estimation of Fe²⁺, H₂O₂, and other reducing agents. Record the exact normality for accurate calculations in subsequent experiments.

Preparation and Standardization of 0.1N KMnO4 Solution