To standardize the given approximate N/10 KMnO4 standard oxalic solution (Redox titration) | NEB Grade XII Chemistry Practical | Nepali Educate

Experiment Number: 07
TITLE: TO STANDARDIZE THE GIVEN APPROXIMATE N/10 KMNO₄ STANDARD OXALIC SOLUTION (REDOX TITRATION) APPARATUS REQUIRED:

1. Burette,
2. Funnel,
3. Conical Flask,
4. Beakers,
5. Pipette,
6. Burner.

CHEMICALS USED:

1. KMNO₄,
2. H₂SO₄,
3. Oxalic Acid.

THEORY

Standardization involves determining the concentration of an unknown solution using a primary standard solution by identifying the reaction's endpoint. The reaction between acidified KMnO₄ and oxalic acid solution is a redox reaction. Redox titration refers to the titration between an oxidizing and a reducing agent. The concentration of an unknown KMnO₄ solution is determined by titrating it against a specific volume of oxalic acid. At the endpoint, the KMnO₄ solution retains its characteristic pink color. Thus, potassium permanganate serves as a self-indicator.

REACTION INVOLVED:

2 KMnO₄ + 3 H₂SO₄ + 5 (COOH)₂ ⟶ K₂SO₄ + 2 MnSO₄ + 8 H₂O + 10 CO₂

In this reaction, \(H_2SO_4\) acts as the acidifying agent. Here, manganese is reduced from \(+7\) oxidation state to \(+2\) state by gaining 5 electrons.

The equivalent weight of KMnO₄ is calculated by dividing the molecular weight by 5:

\[ \text{Equivalent weight of KMnO}_4 = \frac{158}{5} = 31.6 \]

For the 250 mL of approximately \(N/10\) KMnO₄ solution, the weight required is:

\[ \text{Weight required} = \left( \frac{31.6 \times 250 \times 1}{10} \right) / 1000 \]

The strength of the prepared \(KMnO_4\) solution is determined by using the normality equation:

\[ S_1 \times V_1 = S_2 \times V_2 \]

where,
\(S_1\) = Normality of oxalic acid,
\(V_1\) = Volume of oxalic acid,
\(S_2\) = Normality of \(KMnO_4\) solution,
\(V_2\) = Volume of \(KMnO_4\) solution used.

PROCEDURE:

The burette was rinsed with water followed by a KMnO₄ solution and then filled with KMnO₄ solution up to the mark. 25 mL of standard oxalic acid solution was pipetted into a 250 mL conical flask, and about 10 mL of bench sulfuric acid was added to it. The oxalic acid was warmed to about 65°C to increase the rate of reaction. The KMnO₄ solution was titrated into the oxalic acid with constant shaking. At the endpoint, the pink color persisted for 30 seconds. The volume of KMnO₄ solution consumed was noted, and the procedure was repeated for two consecutive readings.

OBSERVATION TABLE:

S.No.	Volume of oxalic acid taken (mL)	Burette reading (mL)			Concurrent Reading
		Initial	Final	Difference
1.	25.0	0	12.1	12.1	12.6
2.	25.0	12.1	24.7	12.6
3.	24.7	12.6	37.3	12.6

CALCULATION:

Volume of acid taken (\(V_1\)) = 25 mL

Normality of oxalic acid (\(S_1\)) = 1/10 N

Volume of KMnO_y solution (\(V_2\)) = 12.6 mL

Normality of KMnO₄ (\(S_2\)) = ?

We have:

\[S_1 \times V_1 = S_2 \times V_2\] \[\Rightarrow S_2 = \frac{S_1 \times V_1}{V_2} = \frac{1/10 \times 25}{12.6} = 0.019 \text{ N}\] RESULT:

Hence, the KMnO_y solution was standardized, and the concentration was found to be 0.19 N.

CONCLUSION:

Redox titration can be carried out without using an indicator.

PRECAUTIONS:

1. Temperature should not be too high.
2. Dil.H₂SO₄ should be added sufficiently
3. End point should be noted accurately.