Prepare M/20 Solution of Ferrous Ammonium Sulphate (Mohr’s salt). Using this Solution Find out the Molarity and Strength of the Given KMnO4  Solution

Chemical Equations

KMnO4 is a self-indicator.

End Point
Colourless to permanent pink colour (KMnO4 in burette).


  1. Prepare 250 ml of M/20 Mohr’s salt solution by dissolving 4.9 g of Mohr’s salt in water 20 as described in experiment 11.3. Rinse the pipette with the M/20 Mohr’s salt solution and pipette out 20.0 ml of it in a washed titration flask.
  2. Rinse and fill the burette with the given KMn04 solution.
  3. Add one test-tube (~ 20 ml) full of dilute sulphuric acid (~ 2 M) to the solution in titration flask.
  4. Note the initial reading of the burette.
  5. Now add KMnO4 solution from the burette till a permanent light pink colour is imparted to the solution in the titration flask on addition of last single drop of KMnO4 solution.
  6. Note the final reading of the burette.
  7. Repeat the above steps 4-5 times to get a set of three concordant readings.

Weight of watch glass =……. g
Weight of watch glass + Mohr’s salt =…………..g
Weight of Mohr’s salt = 4.90 g
Volume of Mohr’s salt solution prepared = 250 ml
Molarity of Mohr’s salt solution = M/20
Volume of Mohr’s salt solution taken for each titration = 20.0 ml

(a) Molarity of the KMnO4 solution.
From the overall balanced chemical equation, it is clear that 2 moles of KMnO4 reacts with 10 moles of Mohr’s salt.

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