titration of kmno4 with mohr's salt class 12 | determine the concentration of KMnO4 using mohr salt

Summary

The video demonstrates how to determine the unknown concentration of potassium permanganate (KMnO₄) by titrating it against a known solution of Mohr’s salt in acidic conditions.

Materials and setup

• Conical flask
• 0.01 M Mohr’s salt solution
• Dilute sulfuric acid (H₂SO₄)
• 50 mL pipette and 50 mL burette
• Iron stand and funnel
• KMnO₄ solution of unknown concentration
• Magnetic stirrer and magnetic bar

Procedure

1. Pipette 20 mL of 0.01 M Mohr’s salt into a conical flask.
2. Add 20 mL of dilute H₂SO₄ to provide acidic conditions.
3. Secure the burette to the stand and fill it with the unknown KMnO₄ solution using a funnel.
4. Place a magnetic bar in the flask and set it on the magnetic stirrer. The video uses a stirring speed of 150 rpm.
5. Gradually add KMnO₄ from the burette while stirring.
6. Stop when a light pink colour appears and persists, indicating the endpoint.
7. Record the volume of KMnO₄ used. In the example, it is 4 mL.

Reaction and calculation

In acidic solution, permanganate oxidizes the iron(II) ions in Mohr’s salt to iron(III). The mole ratio is:

2 mol KMnO₄ : 10 mol Fe²⁺

Using the formula shown in the video:

[ \frac{M_{\mathrm{KMnO_4}}V_{\mathrm{KMnO_4}}}{2} = \frac{M_{\mathrm{Mohr’s\ salt}}V_{\mathrm{Mohr’s\ salt}}}{10} ]

Substituting the example values:

[ \frac{M_{\mathrm{KMnO_4}}\times 4}{2} = \frac{0.01\times 20}{10} ]

This gives an estimated KMnO₄ concentration of 0.01 M.

Speakers or sources

• Narrator/presenter: Source of Skills. No other speakers are featured.