Oxalic acid (C2H2O4) is a common primary standard in analytical chemistry. It can prepare molar and normal solutions for various titrations and analytical procedures. Here, we’ll outline the steps to prepare and standardize molar (1.0 M) and normal (1.0 N) oxalic acid solutions.
Preparation of a 1.0 M oxalic acid solution
A 1.0 M oxalic acid solution contains one mole of oxalic acid in one liter of solution.
Materials Required:
Oxalic acid dihydrate (C2H2O4·2H2O)
Distilled water
A balance
A glass stirring rod
A glass or plastic container
A 1.0-liter volumetric flask
Procedure:
- Weigh 126.07 grams of oxalic acid dihydrate (126.07 g/mol) for a 1.0 M solution in a clean container. Ensure precise measurement.
- Transfer the oxalic acid into a clean, dry glass or plastic container.
- Dissolve the oxalic acid in distilled water with stirring until it’s fully dissolved, resulting in a volume less than 1.0 L.
- Transfer the solution to a 1.0 L volumetric flask. Rinse the container with distilled water to transfer all the oxalic acid.
- Fill the volumetric flask to the 1.0 L mark with distilled water, maintaining a consistent temperature (usually 20°C). Your solution is now a 1.0 M oxalic acid solution.
Standardization of 1.0 M Oxalic Acid Solution to Prepare 1.0 N Solution:
To standardize the 1.0 M oxalic acid solution and prepare a 1.0 N solution, you’ll need to determine its exact molar concentration.
Materials Required:
– Potassium permanganate (KMnO4)
– Sulfuric acid (H2SO4)
– A burette
– A balance
– A 1.0 L volumetric flask
Procedure:
- Accurately weigh approximately 3.16 grams of potassium permanganate (KMnO4) with a known purity. The molar mass of KMnO4 is 158.04 g/mol.
- Dissolve the weighed KMnO4 in distilled water and transfer it into a 1.0 L volumetric flask.
- Add sulfuric acid (H2SO4) to the volumetric flask to acidify the solution and prevent the reduction of KMnO4 by any impurities or substances in the solution.
- Prepare the burette with the 1.0 M oxalic acid solution.
- Titrate the KMnO4 solution with the oxalic acid solution using the balanced chemical equation:
Equation
5(C2H2O4) + 2(KMnO4) + 3(H2SO4) -> 10(CO2) + 2(MnSO4) + 8(H2O) + 2(K2SO4)
- The endpoint is reached when the pink color of the KMnO4 solution becomes colorless, indicating a complete reaction.
- Record the volume of oxalic acid solution used for the titration. Use this volume to calculate the exact molar concentration of the oxalic acid solution.
- If the calculated molarity is close to 1.0 M, consider the solution as a 1.0 N oxalic acid solution. If not, adjust the concentration and re-standardize if necessary.
