Titrations in which a reducing agent is titrated against an oxidizing agent or vice versa are called Redox titration. In a redox reaction if one substance is oxidized the other is reduced. Oxidation is defined as the process in which loss of electron from the element takes place and reduction is a process where electrons are accepted by the element or the ion. The reagent which undergoes reduction is an oxidizing agent and the reagent which undergoes oxidation is a reducing agent. The oxidation and reduction are complementary to one another and takes place simultaneously.
Here in the Experiment Fe2+ is oxidized to Fe3+ & MnO4– is reduced to Mn2+.
MnO4 − + 8H+ + 5e = Mn2+ + 4H2O …………. Reduction
[ Fe2+ – e = Fe3+ ] x 5 ………. Oxidation
MnO4 − +5Fe2+ +8H+ = Mn2+ +5Fe3++ 4H2O
Chemicals: Mohr’s salt, KMnO4 solution, 1(N) H2SO4, Syrupy H3PO 4, Distilled water.
Apparatus: Burette, Pipette, 250 ml conical flask, Measuring Cylinder, Dropper.
- Pipette out 10 ml of Mohr’s salt & taken In a 250 ml conical flask,
- Add 20 ml 1(N) H2 SO4 solution & 30 ml of distilled water followed by 1 ml of syrupy phosphoric acid (H3PO4).
- The solution is allowed to titrate with standard KMnO4 solution drop wise taken in a burette, until the colour of the solution turns from colour less to faint pink.
Repeat the process thrice.
|No. of obs.||Vol. of Mohr’s salt||Burette reading||Vol. of KMnO4||Mean Vol. of KMnO4
| Strength of KMnO4
1000 ml 1(N) of KMnO4 55.85 gm of Fe(II)
X ml Y (N) of KMnO4 55.85x XY / 5 gm of Fe(II)
= Z (say)
Hence, 10 ml of Mohr’s salt contains Z gm of Fe (II)
1000 ml of Mohr’s salt contains (Z x 100) gm of Fe (II).
Conclusion: Hence, Given Mohr’s salt contains ……… gm/lit of Fe (II).
i) Use of the balance should be done carefully.
ii) Use of syrupy phosphoric acid should be done carefully