Experiment 173

Objective

Determine the concentration of a (M/20) potassium permanganate (KMnO₄) solution by titration against a standard oxalic acid solution.

Introduction

Oxalic acid is a primary standard, meaning it can be prepared to a precise concentration. Potassium permanganate (KMnO₄), on the other hand, is a secondary standard and requires standardization. This experiment utilizes the reaction between oxalic acid and KMnO₄ to determine the strength of the KMnO₄ solution.

Reaction Equation:

2KMnO4 + 3H2SO4 + 5HOOC – COOH → K2SO4 + 10CO4 + H2O

In this equation, 2 moles of KMnO₄ react with 5 moles of oxalic acid.

Formula Used:

V1 ​× 2M1 ​= V2​ × 5M2​

Where:

V1: Volume of oxalic acidM1​: Molarity of oxalic acidV2​: Volume of KMnO₄V2​: Molarity of KMnO₄

KMnO₄ serves as the indicator in this titration, where a color change from pink to colorless marks the endpoint.

Materials

Chemicals

·       Sulfuric acid (H₂SO₄)

·       Distilled water

·       Potassium permanganate (KMnO₄)

·       Oxalic acid (HOOC-COOH)

Apparatus

·       250 mL beaker

·       Pipette

·       Burette

·       Stand

·       Bunsen burner

Preparation of Reagents

·       Dissolve 10.8 g of potassium permanganate in 500 mL of distilled water to create the KMnO₄ solution.

·       Prepare an (M/20) oxalic acid solution.

Procedure

1.    Wash the pipette, burette, and conical flask thoroughly.

2.    Fill the burette with the KMnO₄ solution.

3.    Use the pipette to transfer 25 mL of the oxalic acid solution into the flask.

4.    Add 20 mL of dilute sulfuric acid to the flask.

5.    Titrate by adding the KMnO₄ solution dropwise to the flask until the solution turns colorless, indicating the endpoint.

6.    Repeat the titration 2–3 times to ensure consistent results.

Observation and Calculation

·       Observed Volume of KMnO₄ Required: 25.43 mL

·       Given values:

·       V1​ = 25 mL

·       M1​ =1.02 × (M/20)

·       V2​ = 25.43 mL

Using the formula:

M2 = 2 x V1 x M1 / 5 x V2

Substitute the values:

= M2 = 2 X 25 x 1.02 / 5 x 25.45 = 0.02 M

Conclusion:

The concentration of the potassium permanganate solution is 0.02 M or 0.04 (M/20).

Questions

1.    What is potassium permanganate?

2.    What color is observed for potassium permanganate?

3.    Define titration.

4.    Which indicator is used in KMnO₄ titration?

5.    What is an indicator?