Detailed Procedure and Calculations for Oxalic Acid vs KMnO4 Titration
The Titration Of Oxalic Acid With Kmno4 is a classic redox titration commonly featured in class 12 chemistry practicals. In this experiment, a known concentration of oxalic acid is titrated against a potassium permanganate solution in acidic medium, allowing for the precise determination of its concentration. This method utilizes the self-indicating property of potassium permanganate, making the endpoint visible through a color change. Mastering this common analytical technique is vital for understanding oxidation-reduction reactions, quantitative analysis, and laboratory procedures. Here, we break down the underlying principles, procedures, key equations, calculations, and important precautions for successful execution and exam preparation.
Theory Behind Redox Titration: Oxalic Acid and Potassium Permanganate
The titration of oxalic acid with KMnO4 is based on a redox reaction in acidic medium. Here, oxalic acid acts as a reducing agent, while potassium permanganate is the oxidizing agent. The entire process is visually tracked by the disappearance and reappearance of the characteristic purple color of permanganate ions.
Key Principles and Balanced Equations
- Reaction occurs only in acidic conditions, provided by dilute sulfuric acid.
- Potassium permanganate solution is purple; upon reduction, Mn2+ formed is nearly colorless.
- No external indicator is needed, as KMnO4 is self-indicating.
The overall chemical equation is:
$$ 2KMnO_4 + 5H_2C_2O_4 + 3H_2SO_4 \rightarrow K_2SO_4 + 2MnSO_4 + 10CO_2 + 8H_2O $$
The ionic redox reaction is:
$$ 2MnO_4^- + 16H^+ + 5C_2O_4^{2-} \rightarrow 2Mn^{2+} + 10CO_2 + 8H_2O $$
Step-by-Step Procedure
For accurate readings and exam-ready observation tables, follow each step consistently:
- Preparation of standard oxalic acid: Weigh 12.6 g oxalic acid, dissolve it in distilled water, and make up the volume to 1 L for a 0.1 M solution.
- Fill a clean burette with potassium permanganate solution.
- Pipette 10 mL of oxalic acid into a conical flask. Add about 5 mL of 1M dilute sulfuric acid.
- Heat the flask contents to around 55–60°C to speed up the reaction.
- Place the flask on a white tile for clear visibility of color changes.
- Titrate by adding KMnO4 dropwise, swirling continuously. Initially, the purple color disappears; the endpoint is signaled by the faint persistent pink color.
- Record burette readings and repeat for concordant results, filling in your titration of oxalic acid with KMnO4 observation table lab.
Observation Table and Key Calculations
A typical titration of oxalic acid with KMnO4 observation table records:
- Volume of oxalic acid solution taken for each titration.
- Initial and final burette readings for KMnO4.
- Volume of KMnO4 used (final - initial).
To calculate the unknown molarity (M2 for KMnO4):
$$ a_1M_1V_1 = a_2M_2V_2 $$
- a1 = 2 (electrons lost per oxalic acid molecule)
- a2 = 5 (electrons gained per permanganate ion)
- M1, V1: molarity and volume of oxalic acid
- M2, V2: molarity and volume of KMnO4
$$ M_2 = \frac{2M_1V_1}{5V_2} $$
For a detailed breakdown of redox titration concepts, visit redox titration procedure.
Precautions and Practical Tips
- Thoroughly rinse all glassware before use (volumetric analysis precautions).
- Use only sulfuric acid for acidification—avoid HCl or HNO3 as they interfere with the reaction.
- Maintain oxalic acid temperature at 50–60°C for a smooth, observable endpoint.
- Take upper meniscus reading for KMnO4 due to its intense color.
- Be precise—avoid parallax error and ensure consistent swirling.
Related Chemistry Concepts
- Review properties of oxalic acid and its applications.
- Understand KMnO4 chemistry and handling.
- For redox and other titration types, see titration methods overview.
For more basic chemical reactions involved in acid-base titrations, refer to acids, bases, and salts in chemistry.
In summary, the titration of oxalic acid with KMnO4 is a foundational experiment for understanding redox principles, careful laboratory methods, and calculations using mole concepts. Performing this titration improves your skills in observation, recording data, and analytical reasoning. Whether preparing for class 12 exams or future lab work, mastering this technique helps you grasp essential ideas in chemistry. Keep practicing, and revisit the titration of oxalic acid with KMnO4 viva questions to deepen your understanding and ace your practical exams.
FAQs on How to Perform Titration of Oxalic Acid with Potassium Permanganate
1. What is the principle of titration of oxalic acid with KMnO4?
The titration of oxalic acid with potassium permanganate (KMnO4) is based on a redox reaction where KMnO4 acts as an oxidizing agent and oxalic acid as a reducing agent.
Key points:
- The reaction occurs in an acidic medium, usually with dilute sulfuric acid.
- KMnO4 is reduced to Mn2+ ions, while oxalic acid is oxidised to CO2 and H2O.
- KMnO4 acts as its own indicator due to its violet/pink colour, which disappears as it reacts.
2. How do you perform the titration of oxalic acid with KMnO4 in the laboratory?
The titration of oxalic acid with KMnO4 involves accurate preparation, heating, and careful addition of solutions for precise results.
Procedure:
- Fill a burette with standard KMnO4 solution.
- Take a measured volume of oxalic acid solution in a conical flask.
- Add dilute H2SO4 to acidify the medium.
- Heat the mixture to about 60-70°C to speed up the reaction.
- Titrate by adding KMnO4 drop by drop until a persistent pale pink colour appears, indicating the endpoint.
3. Why is the oxalic acid solution heated before titrating with KMnO4?
Heating oxalic acid solution is essential during KMnO4 titration to increase the reaction rate.
Reasons:
- The redox reaction between KMnO4 and oxalic acid is slow at room temperature.
- Heating to 60–70°C ensures complete and efficient oxidation of oxalic acid.
- It provides a sharp and accurate endpoint.
4. What is the balanced chemical equation for the reaction between KMnO4 and oxalic acid?
The balanced chemical equation for the titration of oxalic acid with KMnO4 in acidic medium is:
2 KMnO4 + 3 H2SO4 + 5 (COOH)2 → K2SO4 + 2 MnSO4 + 10 CO2 + 8 H2O
This shows that KMnO4 oxidises oxalic acid to CO2 in the presence of dilute H2SO4.
5. Why is dilute sulfuric acid used in the titration of oxalic acid with KMnO4?
Dilute sulfuric acid is added during KMnO4 titration with oxalic acid to provide the acidic medium necessary for the redox reaction.
Key points:
- It ensures that KMnO4 acts as a strong oxidising agent.
- Prevents side reactions such as the formation of brown MnO2 precipitate.
- Other acids like HCl are avoided, as they can be oxidised by KMnO4, leading to errors.
6. What is the endpoint in the titration of oxalic acid with KMnO4 and how is it detected?
The endpoint in KMnO4–oxalic acid titration is identified by a permanent pale pink colour in the solution.
Detection:
- The pink colour appears when all the oxalic acid is oxidised and excess KMnO4 remains unreacted.
- This colour persists for at least 30 seconds, indicating titration completion.
7. Which indicator is used in the titration of oxalic acid with KMnO4?
No external indicator is used in the titration of oxalic acid with KMnO4 because KMnO4 itself acts as a self-indicator.
Details:
- KMnO4 has an intense purple-violet colour.
- The solution turns colourless on reaction, and a faint pink colour marks the endpoint.
8. Calculate the normality of oxalic acid if 25 ml of oxalic acid reacts completely with 30 ml of 0.05 N KMnO4.
To calculate the normality of oxalic acid in this titration, use the equivalence principle:
N1V1 = N2V2
Given:
- V1 = 25 ml (oxalic acid)
- N2 = 0.05 N (KMnO4)
- V2 = 30 ml (KMnO4)
N1 × 25 = 0.05 × 30
N1 = (0.05 × 30) / 25 = 0.06
So, the normality of oxalic acid is 0.06 N.
9. What precautions should be taken during the titration of oxalic acid with KMnO4?
Certain precautions ensure accuracy during KMnO4 titration with oxalic acid.
Essential steps:
- Heat the reaction mixture to 60–70°C before titration.
- Always add KMnO4 from the burette to the oxalic acid solution.
- Avoid using strong acids other than dilute H2SO4.
- Stir continuously for uniform mixing.
- Add KMnO4 slowly near the endpoint for accuracy.
10. What is the role of KMnO4 in the titration with oxalic acid?
KMnO4 acts as a strong oxidising agent in the titration with oxalic acid in acidic medium.
Functions:
- Oxidises oxalic acid to carbon dioxide and water.
- Self-indicates the endpoint by pink colour.
- Reduces itself from MnO4⁻ to Mn2+ ion.
11. Why is potassium permanganate used as an oxidising agent in redox titrations?
Potassium permanganate (KMnO4) is preferred in redox titrations due to its strong oxidising ability and self-indicating property.
Key points:
- It readily oxidises many reducing agents including oxalic acid, FeSO4, etc.
- It changes colour from violet to colourless (and then faint pink), marking endpoint without an external indicator.
- Gives sharp, observable, and accurate titration results.
