Determine the exact molarity of Oxalic acid solution Volumetrically

Learn how to accurately determine the molarity of an oxalic acid solution using volumetric titration with a standard sodium hydroxide solution and phenolphthalein indicator.

Abstract

This chemistry practical focuses on finding the exact molarity of a given oxalic acid (H₂C₂O₄) solution by titrating it with a standard sodium hydroxide (NaOH) solution. The experiment uses phenolphthalein as an acid-base indicator and follows a simple titration procedure commonly taught in high school and college chemistry labs.

Materials Required

• Oxalic acid solution (unknown concentration)
• Standard NaOH solution (0.1 M)
• Phenolphthalein indicator
• Burette, pipette, conical flask, beaker
• Distilled water
• Clamp stand, funnel

Procedure (Step-by-Step)

1. Rinse and fill the burette with 0.1 M sodium hydroxide solution.
2. Use a pipette to transfer exactly 25 ml of oxalic acid into a clean conical flask.
3. Add 2–3 drops of phenolphthalein to the oxalic acid.
4. Slowly titrate by adding NaOH from the burette while swirling the flask gently.
5. Watch for a permanent light pink color, indicating the endpoint.
6. Note the volume of NaOH used.
7. Repeat until at least two concordant readings are obtained.

Observation Table

Reading No.	Initial Burette Reading (ml)	Final Burette Reading (ml)	Volume of NaOH Used (ml)
1	0.0	23.8	23.8
2	0.0	24.0	24.0
3	0.0	23.9	23.9

Calculation of Molarity

Balanced Chemical Equation:
H₂C₂O₄ + 2NaOH → Na₂C₂O₄ + 2H₂O

Given:
Average volume of NaOH used = 23.9 ml = 0.0239 L
Molarity of NaOH = 0.1 M
Volume of oxalic acid = 25 ml = 0.025 L

Formula:
M₁V₁/n₁ = M₂V₂/n₂
(0.1 × 0.0239)/2 = M_oxalic × 0.025
⇒ M_oxalic = (0.1 × 0.0239 × 1) / (2 × 0.025) = 0.0478 M

Result

The calculated molarity of the given oxalic acid solution is 0.0478 M.

Chemical Reaction Equation

H2C2O4 + 2NaOH → Na2C2O4 + 2H2O

20 Short Conceptual Questions

1. What is molarity?
2. Define titration.
3. Which indicator is used in this experiment?
4. Why is phenolphthalein suitable here?
5. What is the endpoint color in this titration?
6. What is meant by a standard solution?
7. What is the molecular formula of oxalic acid?
8. What role does NaOH play in this titration?
9. Define a concordant reading.
10. State the balanced chemical equation for the reaction.
11. How many moles of NaOH react with one mole of oxalic acid?
12. Why is titration repeated?
13. How do you calculate the average of readings?
14. Why is oxalic acid a dibasic acid?
15. What is the SI unit of molarity?
16. Can methyl orange be used in this titration?
17. What is the function of a burette?
18. What is the purpose of a pipette?
19. Why is a conical flask used in titration?
20. Explain how molarity is calculated from titration data.

5 Multiple Choice Questions (MCQs)

1. Which indicator is used in this titration?
   Ⓐ Methyl orange Ⓑ Phenolphthalein Ⓒ Litmus Ⓓ None
   Answer: Ⓑ Phenolphthalein
2. Color at the endpoint in this experiment is:
   Ⓐ Pink to colorless Ⓑ Colorless to pink Ⓒ Yellow to red Ⓓ Blue to green
   Answer: Ⓑ Colorless to pink
3. Oxalic acid reacts with NaOH in what ratio?
   Ⓐ 1:1 Ⓑ 1:2 Ⓒ 2:1 Ⓓ 2:2
   Answer: Ⓑ 1:2
4. The unit of molarity is:
   Ⓐ mol/kg Ⓑ mol/L Ⓒ g/L Ⓓ g/mol
   Answer: Ⓑ mol/L
5. The chemical formula of oxalic acid is:
   Ⓐ H₂SO₄ Ⓑ CH₃COOH Ⓒ H₂C₂O₄ Ⓓ HNO₃
   Answer: Ⓒ H₂C₂O₄

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