Question

Determine the molarity of the given KMnO$_4$ solution with the help of supplied Mohr's salt solution by titration method.

Hint:

Always perform the titration slowly near the endpoint to avoid overshooting the pink color.

Answer 1

Aim.
To determine the molarity of the given KMnO$_4$ solution using Mohr's salt solution (Fe$^{2+}$).
Apparatus.
Burette, conical flask, pipette, Bunsen burner, test tube, HCl, H$_2$SO$_4$, Mohr's salt solution.
Procedure.
1. Fill the burette with the KMnO$_4$ solution.
2. Take a known volume of Mohr’s salt solution (Fe$^{2+}$) in a conical flask.
3. Add a few drops of dilute H$_2$SO$_4$ to provide H$^+$ for the reaction.
4. Titrate the KMnO$_4$ solution into the Mohr’s salt solution while stirring continuously.
5. A persistent pink color will appear near the endpoint. This indicates that all the Fe$^{2+}$ has reacted, and the endpoint is reached.
6. Note the volume of KMnO$_4$ used.
Calculation.
Using the equation: \[ M_1V_1 = M_2V_2 \] Where: - \(M_1\) = Molarity of KMnO$_4$ - \(V_1\) = Volume of KMnO$_4$ used in titration - \(M_2\) = Molarity of Mohr's salt solution - \(V_2\) = Volume of Mohr's salt solution used in titration Since the balanced reaction between KMnO$_4$ and Mohr's salt is: \[ 2MnO_4^- + 5Fe^{2+} \rightarrow 2Mn^{2+} + 5Fe^{3+} \] The molar ratio between KMnO$_4$ and Fe$^{2+}$ is 2:5.