Question

Standardize the KMnO4 using 0.1M (NH4)2(FE(SO4)26H2O (remember dissolve in H2SO4)

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Answer 1

In titration of Potassium permanganate by Mohr's salt (in presence of sulfuric acid) Potassium permanganate act as oxidising agent whereas Mohr's salt act as reducing agent.

Potassium permanganate is the self indicator giving rise to light pink color indicating end point.

Ionic redox reaction :

Fe​​​​​2+ Fe​​​​​3+ + e × 5 oxidation half reaction

MnO​​​​4 - + 8H+ + 5e  Mn​​​​​2+ + 4H2O reduction half reaction

MnO​​​​4 - + 5 Fe​​​​​2+ + 8H+ 5 Fe​​​​​3+ + Mn​​​​​2+ + 4H2O

Given strength of Mohr's salt solution is 0.1 (M).

Set up :

The titrationn should be start with taking Potassium permanganate solution in burette as a titrant and Mohr's salt solution in conical flask as a titre.

The addition of Potassium permanganate solution to Mohr's salt solution should be controlled and Swift.

Calculations :

Say, x mL of given Potassium permanganate solution is used to neutralize y mL of 0.1 (M) Mohr's salt solution.

Using formula of equivalence we write ,

N​​​​​​1 M​​​​​​1 V​​​​​​1 = N 2 M 2 V 2

n​​​​​1 M​​​​​​1 V​​​​​1 = n​2 M 2 V 2.   

[ Normality (N) = no of e transfer (n) × Molarity (M) ]

Where n​​​​​​1 and n​​​​​​2 are number of electron transfer in oxidation and reduction half reactions ; M​​​​​​1 , M​​​​​​2 ​​​​​​and V 1 , V 2  are Molarity of Mohr's salt and Potassium permanganate respectively.

Hence the strength of Potassium permanganate solution can be determined by using Mohr's salt solution of known strength.