Activity Project: Preparation and Standardization of Sodium Hydroxide (NaOH) Solution

Objective

To prepare approximately 0.1 M sodium hydroxide solution and standardize it using a primary standard oxalic acid solution through titration.

Materials Required

• Sodium hydroxide pellets (NaOH)
• Oxalic acid dihydrate (H₂C₂O₄·2H₂O) – primary standard
• Distilled water
• Phenolphthalein indicator
• Burette, pipette, conical flask, beaker
• Weighing balance

Procedure

1. Preparation of NaOH solution: Weigh about 4 grams of NaOH pellets and dissolve it in 1 litre distilled water to prepare approximately 0.1 M solution.
2. Filter the solution to remove impurities or undissolved particles.
3. Preparation of oxalic acid solution: Accurately weigh about 1.26 g oxalic acid dihydrate and dissolve in 250 mL distilled water to make approximately 0.05 M solution.
4. Using a pipette, transfer 25 mL of oxalic acid solution into a conical flask.
5. Add 2-3 drops of phenolphthalein indicator to the oxalic acid solution.
6. Fill the burette with sodium hydroxide solution, ensuring no air bubbles.
7. Slowly add NaOH from the burette into the oxalic acid solution, swirling constantly.
8. Titrate until a faint pink color persists for at least 30 seconds, indicating the endpoint.
9. Record the volume of NaOH used.
10. Repeat titration to get at least 3 concordant readings.

Observations

Titration No.	Volume of Oxalic Acid (mL)	Volume of NaOH Used (mL)	Color Change at Endpoint	Remarks
1	25.0	24.6	Colorless to faint pink	Accurate endpoint
2	25.0	24.7	Colorless to faint pink	Consistent trial
3	25.0	24.5	Colorless to faint pink	Consistent trial

Calculations

Using the reaction: H₂C₂O₄ + 2NaOH → Na₂C₂O₄ + 2H₂O

The reaction molar ratio is 1:2 between oxalic acid and NaOH.

M₁V₁ × n₁ = M₂V₂ × n₂

Where:
M₁ = Molarity of oxalic acid,
V₁ = Volume of oxalic acid,
n₁ = Number of acidic protons in oxalic acid (2),
M₂ = Molarity of NaOH,
V₂ = Volume of NaOH used,
n₂ = Number of OH⁻ ions (1)
    

Result

The exact molarity of sodium hydroxide solution is calculated based on the volume of acid titrated and volumes recorded.

Precautions

• Prepare NaOH solution fresh as it absorbs moisture and CO₂ slowly from air.
• Standardize NaOH before use due to its instability.
• Slowly add NaOH near endpoint to avoid overshooting.
• Swirl the conical flask continuously during titration.
• Use white tile beneath the flask to observe color change easily.