TITLE: TO STANDARDIZE THE GIVEN APPROXIMATE N/10 KMNO4 STANDARD OXALIC SOLUTION (REDOX TITRATION) APPARATUS REQUIRED:
- Burette,
- Funnel,
- Conical Flask,
- Beakers,
- Pipette,
- Burner.
- KMNO4,
- H2SO4,
- Oxalic Acid.
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.
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 |
Volume of acid taken (\(V_1\)) = 25 mL
Normality of oxalic acid (\(S_1\)) = 1/10 N
Volume of KMnOy 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 KMnOy 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:- Temperature should not be too high.
- Dil.H2SO4 should be added sufficiently
- End point should be noted accurately.