Titration of Oxalic Acid with Sodium Hydroxide (NaOH) – Class 11 Chemistry

Introduction

This is a typical acid-base titration where oxalic acid (a diprotic acid) is titrated against a strong base, sodium hydroxide (NaOH), to determine the concentration of the acid.

Chemicals Required

• Oxalic Acid (H₂C₂O₄·2H₂O) – analyte
• Sodium Hydroxide (NaOH) solution – titrant
• Phenolphthalein or methyl orange indicator
• Distilled water

Chemical Reaction

H₂C₂O₄ + 2NaOH → Na₂C₂O₄ + 2H₂O
    

Oxalic acid is a diprotic acid and requires two moles of NaOH per mole of acid for neutralization.

Apparatus Required

• Burette (filled with NaOH solution)
• Pipette (for measuring oxalic acid solution)
• Conical flask
• Beaker
• White tile (to observe color change)

Preparation of Solutions

• NaOH Solution: Approximately 0.1 M standard solution prepared and standardized if needed.
• Oxalic Acid Solution: Accurately weighed oxalic acid dissolved in distilled water to prepare solution for titration.

Procedure

1. Clean and rinse the burette with NaOH solution, then fill it.
2. Using a pipette, take a known volume (e.g., 25 mL) of oxalic acid solution into a clean conical flask.
3. Add 2-3 drops of phenolphthalein indicator to the flask.
4. Place the flask on a white tile for better visibility.
5. Add NaOH solution from the burette gradually to the oxalic acid solution while swirling constantly.
6. The indicator will remain colorless until near neutralization, then changes to pink, indicating the endpoint.
7. Note the volume of NaOH used at the first permanent pink color.
8. Repeat the titration until consistent readings are obtained.

Observation Table

Titration No.	Volume of Oxalic Acid (mL)	Volume of NaOH Added (mL)	Color Change at Endpoint	Remarks
1	25.0	23.5	Colorless to faint pink	Accurate endpoint
2	25.0	23.4	Colorless to faint pink	Consistent trial
3	25.0	23.6	Colorless to faint pink	Consistent trial

Calculations

The reaction ratio is 1 mole oxalic acid reacts with 2 moles of NaOH.

Formula:

M₁V₁ × n₁ = M₂V₂ × n₂

Where: 

M₁ = Molarity of oxalic acid, V₁ = Volume of oxalic acid,

n₁ = Number of acidic protons in acid (2 for oxalic acid),

M₂ = Molarity of NaOH, V₂ = Volume of NaOH used,

n₂ = Number of hydroxide ions (1 for NaOH)
    

Result

The concentration (molarity) of oxalic acid solution can be calculated using the volume of NaOH consumed.

Precautions

• Use freshly prepared NaOH solution, standardized if possible.
• Add NaOH slowly near the endpoint to avoid overshooting.
• Swirl the conical flask constantly for uniform mixing.
• Use appropriate indicator like phenolphthalein for a clear endpoint.
• Take multiple readings for accuracy.