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)
- Rinse and fill the burette with 0.1 M sodium hydroxide solution.
- Use a pipette to transfer exactly 25 ml of oxalic acid into a clean conical flask.
- Add 2–3 drops of phenolphthalein to the oxalic acid.
- Slowly titrate by adding NaOH from the burette while swirling the flask gently.
- Watch for a permanent light pink color, indicating the endpoint.
- Note the volume of NaOH used.
- 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 = Moxalic × 0.025
⇒ Moxalic = (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
- What is molarity?
- Define titration.
- Which indicator is used in this experiment?
- Why is phenolphthalein suitable here?
- What is the endpoint color in this titration?
- What is meant by a standard solution?
- What is the molecular formula of oxalic acid?
- What role does NaOH play in this titration?
- Define a concordant reading.
- State the balanced chemical equation for the reaction.
- How many moles of NaOH react with one mole of oxalic acid?
- Why is titration repeated?
- How do you calculate the average of readings?
- Why is oxalic acid a dibasic acid?
- What is the SI unit of molarity?
- Can methyl orange be used in this titration?
- What is the function of a burette?
- What is the purpose of a pipette?
- Why is a conical flask used in titration?
- Explain how molarity is calculated from titration data.
5 Multiple Choice Questions (MCQs)
- Which indicator is used in this titration?
Ⓐ Methyl orange Ⓑ Phenolphthalein Ⓒ Litmus Ⓓ None
Answer: Ⓑ Phenolphthalein - Color at the endpoint in this experiment is:
Ⓐ Pink to colorless Ⓑ Colorless to pink Ⓒ Yellow to red Ⓓ Blue to green
Answer: Ⓑ Colorless to pink - Oxalic acid reacts with NaOH in what ratio?
Ⓐ 1:1 Ⓑ 1:2 Ⓒ 2:1 Ⓓ 2:2
Answer: Ⓑ 1:2 - The unit of molarity is:
Ⓐ mol/kg Ⓑ mol/L Ⓒ g/L Ⓓ g/mol
Answer: Ⓑ mol/L - The chemical formula of oxalic acid is:
Ⓐ H2SO4 Ⓑ CH3COOH Ⓒ H2C2O4 Ⓓ HNO3
Answer: Ⓒ H2C2O4
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