Preparation and Standardization of Oxalic Acid Molar and Normal Solutions

Introduction

Oxalic acid is a widely used primary standard in volumetric analysis, particularly in acid-base and redox titrations. It is a dicarboxylic acid with the molecular formula C₂H₂O₄. It is commonly available in its dihydrate form (C₂H₂O₄·2H₂O). Due to its high purity, stability, and ease of handling, oxalic acid is an ideal reagent for preparing standard solutions used in laboratory applications.

Oxalic acid is not only a primary standard but also plays a vital role in various analytical applications, including complexometric and precipitation titrations. Its precise molar mass and predictable dissociation behavior make it a reliable choice for standardization in quantitative analysis. The dihydrate form (C₂H₂O₄·2H₂O) is commonly preferred due to its defined water content, which simplifies accurate weighing and solution preparation.

Beyond titrimetric analysis, oxalic acid is also employed in metal ion complexation studies and as a key reagent in industrial and pharmaceutical processes. Proper storage in airtight containers prevents moisture absorption and decomposition, ensuring long-term stability.

This article provides a comprehensive guide on the preparation and standardization of oxalic acid molar and normal solutions, including essential calculations and procedural steps.

Preparation of Oxalic Acid Solutions

1. Preparation of 1 M (Molar) Oxalic Acid Solution

Materials Required:

• Oxalic acid dihydrate (C₂H₂O₄·2H₂O)
• Distilled water
• Analytical balance
• 1000 mL volumetric flask
• Glass rod
• Beaker (250 mL)

Apparatus Setup Preparation and Standardization of Oxalic Acid Molar and Normal Solutions

Procedure:

1. Calculation of required oxalic acid mass:
   • The molar mass of Oxalic acid dihydrate (C₂H₂O₄·2H₂O) = 126.07 g/mol.
   • To prepare 1 M solution, dissolve 126.07 g of oxalic acid dihydrate in 1000 mL of distilled water.
2. Weighing the oxalic acid:
   • Using an analytical balance, weigh 126.07 g of oxalic acid dihydrate accurately.
3. Dissolution:
   • Transfer the weighed Oxalic acid to a 250-mL beaker containing about 500 mL of distilled water.
   • Stir the solution until the oxalic acid dissolves completely.
4. Dilution:
   • Transfer the solution to a 1000-mL volumetric flask.
   • Add distilled water up to the mark and mix thoroughly.

2. Preparation of 0.1 N (Normal) Oxalic Acid Solution

Materials Required:

• Oxalic acid dihydrate (C₂H₂O₄·2H₂O)
• Distilled water
• Analytical balance
• 1000 mL volumetric flask

Procedure:

1. Calculation of required oxalic acid mass:
   • Oxalic acid is a diprotic acid; therefore, 1 N solution corresponds to 0.05 M solution.
   • Required oxalic acid mass = (126.07 g/mol) × (0.05 mol/L) = 6.3035 g.
2. Weighing the oxalic acid:
   • Weigh 6.3035 g of Oxalic acid dihydrate accurately.
3. Dissolution:
   • Dissolve the weighed Oxalic acid in about 500 mL of distilled water in a beaker.
   • Stir the solution well until completely dissolved.
4. Dilution:
   • Transfer the solution into a 1000-mL volumetric flask and make up the volume with distilled water.
   • Mix thoroughly.

Standardization of Oxalic Acid Solution

As oxalic acid is a primary standard, it does not require further standardization. However, its concentration can be verified using a standard sodium hydroxide (NaOH) solution.

Materials Required:

• 0.1 N NaOH solution
• Phenolphthalein indicator
• Burette
• Pipette (10 mL)
• Conical flask (250 mL)

Procedure:

1. Pipette out 10 mL of the prepared oxalic acid solution into a conical flask.
2. Add 2-3 drops of phenolphthalein indicator.
3. Fill the burette with a 0.1 N NaOH solution.
4. Titrate the oxalic acid solution with NaOH until a faint pink color persists for 30 seconds.
5. Record the volume of NaOH used.
6. Repeat the titration for three consistent readings.

Calculation of Normality:

Using the formula:

If the calculated normality deviates, adjust by dilution or re-preparation.

Conclusion

Oxalic acid is an essential reagent for titrations in analytical chemistry. Proper preparation and verification of its concentration ensure accurate analytical results. Following standard laboratory protocols, including precise weighing and correct dilution, helps maintain solution integrity. Whether preparing molar or normal solutions, accuracy in concentration is crucial for achieving reproducible results in titrimetric analysis.

Oxalic acid is widely utilized in redox titrations, particularly in permanganometry, due to its well-defined reducing properties. Its standardization against sodium hydroxide or potassium permanganate ensures precise concentration determination. Temperature and storage conditions significantly influence oxalic acid solutions, as decomposition over time can impact accuracy. Additionally, factors such as the purity of oxalic acid, water quality, and environmental conditions play a crucial role in maintaining solution stability. Ensuring proper standardization against a primary standard and regularly verifying concentration enhances the reliability of analytical procedures.