Prepare M/50 Solution of Oxalic Acid. With its help, Determine 50 the Molarity and Strength of the Given Solution of Potassium Permanganate

In this experiment, we will learn:

1. How to prepare an M/50 solution of oxalic acid (H₂C₂O₄).
2. How to use this solution to determine the molarity and strength of a given potassium permanganate (KMnO₄) solution using a titration method.

This process is important in chemistry as it helps in analyzing unknown solutions through a chemical reaction.

Part 1: Preparing an M/50 Solution of Oxalic Acid

What is an M/50 Solution?

• Molarity (M) is a measure of concentration, expressed as moles per liter.
• An M/50 solution means 1/50 of a molar solution, which is 0.02 M (since 1/50 = 0.02).

Molecular Weight of Oxalic Acid (H₂C₂O₄.2H₂O)

• Oxalic acid exists as oxalic acid dihydrate (H₂C₂O₄.2H₂O).
• Its molecular weight is 126 g/mol.

Amount of Oxalic Acid Required

• Formula for mass calculation:
  $$\text{Mass} = \frac{\text{Molecular Weight} \times \text{Molarity} \times \text{Volume (in L)}}{1}$$

  Mass=1Molecular Weight×Molarity×Volume (in L)​

• For M/50 (0.02 M) solution in 1000 mL (1 liter):
  $$\text{Mass} = \frac{126 \times 0.02 \times 1000}{1000} = 2.52 \text{ g}$$

  Mass=1000126×0.02×1000​=2.52 g

Thus, to prepare 1 liter of M/50 oxalic acid solution, dissolve 2.52 g of oxalic acid dihydrate in distilled water and make the volume up to 1000 mL.

Step-by-Step Preparation

1. Weigh 2.52 g of oxalic acid dihydrate using a digital balance.
2. Dissolve it in about 500 mL of distilled water in a beaker.
3. Stir well until fully dissolved.
4. Transfer the solution into a 1-liter volumetric flask.
5. Add distilled water up to the 1000 mL mark.
6. Shake the flask gently to mix the solution properly.
7. The M/50 oxalic acid solution is now ready for use.

Part 2: Determining the Molarity and Strength of a Given Potassium Permanganate (KMnO₄) Solution

We will use titration to find out the molarity of KMnO₄ using the prepared oxalic acid solution.

Principle of Titration

Potassium permanganate (KMnO₄) is a strong oxidizing agent, and oxalic acid (H₂C₂O₄) is a reducing agent. In acidic medium (H₂SO₄), they react as follows:

 

$$2MnO_4^- + 5C_2O_4^{2-} + 16H^+ → 2Mn^{2+} + 10CO_2 + 8H_2O$$

2MnO4−​+5C2​O42−​+16H+→2Mn2++10CO2​+8H2​O

This means 2 moles of KMnO₄ react with 5 moles of oxalic acid.

Step-by-Step Titration Process

Apparatus Required:

• Burette
• Pipette (10 mL)
• Conical flask
• Measuring cylinder
• Funnel
• Distilled water
• Beaker
• Sulfuric acid (H₂SO₄)

Chemicals Required:

• M/50 Oxalic acid solution (prepared earlier)
• Potassium permanganate (KMnO₄) solution (unknown molarity)
• Dilute sulfuric acid (H₂SO₄) for acidic medium

Titration Procedure:

1. Rinse the burette with distilled water and then with the KMnO₄ solution.
2. Fill the burette with KMnO₄ solution and note the initial reading.
3. Pipette 10 mL of M/50 oxalic acid solution into a clean conical flask.
4. Add about 10 mL of dilute sulfuric acid to the flask to maintain an acidic medium.
5. Heat the solution to about 60°C (warm solutions react better).
6. Slowly add KMnO₄ solution from the burette while swirling the flask.
7. The KMnO₄ solution is purple, but when it reacts with oxalic acid, it becomes colorless.
8. The end point is reached when a light pink color remains for 30 seconds.
9. Note the final burette reading.
10. Repeat the titration 2-3 times to get consistent readings.

Part 3: Calculating the Molarity and Strength of KMnO₄ Solution

Using the Titration Formula:

 

$$N_1V_1 = N_2V_2$$

N1​V1​=N2​V2​

Where:

• N₁ = Normality of oxalic acid (M/50 = 0.02 N)
• V₁ = Volume of oxalic acid used (10 mL)
• N₂ = Normality of KMnO₄ (to be found)
• V₂ = Volume of KMnO₄ used (from burette)

 

$$0.02 \times 10 = N_2 \times V_2$$

0.02×10=N2​×V2​

$$N_2 = \frac{0.02 \times 10}{V_2}$$

N2​=V2​0.02×10​

Now, Molarity (M) of KMnO₄ is:

 

$$M = \frac{N}{5}$$

M=5N​

(Since KMnO₄ undergoes a 5-electron change)

After substituting N₂, we get:

 

$$M = \frac{0.02 \times 10}{5 \times V_2}$$

M=5×V2​0.02×10​

Finding the Strength of KMnO₄ Solution

Strength (grams per liter) = Molarity × Molecular Weight of KMnO₄
(Since molecular weight of KMnO₄ = 158 g/mol)

 

$$\text{Strength} = M \times 158$$

Strength=M×158

Thus, we can determine the molarity and strength of the potassium permanganate solution based on the volume used in the titration.

Conclusion

1. We prepared an M/50 solution of oxalic acid by dissolving 2.52 g of oxalic acid dihydrate in 1 liter of water.
2. We performed a redox titration using oxalic acid and KMnO₄ in the presence of sulfuric acid.
3. We used the titration formula to calculate the molarity and strength of the potassium permanganate solution.

This experiment helps us understand how titrations are used to determine unknown concentrations, which is a crucial technique in chemistry.