**Calculate the Percentage of Fe ^{2+} ions in a Sample of Ferrous Sulphate. Prepare a Solution of the given Sample having Strength Exactly Equal to 14.0 g/litre. Provided M/100 KMnO_{4}**

**Chemical Equations**

**Theory**

Since the given sample contains partially oxidized ferrous sulphate, it contains both ferrous ions, Fe^{2+} (unoxidised) and ferric ions Fe^{3+} (oxidised). The strength of partially oxidised sample is known. The solution of partially oxidised FeSO_{4} of known strength is titrated against standard KMnO_{4} solution to determine the molarity and strength of the unoxidised ferrous sulphate. From this the percentage oxidation of the sample can be calculated.

**Indicator**

KMnO_{4} is a self-indicator.

**End Point**

Colourless to permanent pink (KMnO_{4} in burette).

**Procedure**

- Weigh exactly 3.50 g of the given sample of ferrous sulphate on a watch glass and dissolve in water to prepare exactly 250 ml of solution using a 250 ml measuring flask. Rinse and fill the pipette with prepared ferrous sulphate solution and pipette out 20.0 ml of it in a washed titration flask.
- Rinse and fill the burette with the M/100 KMnO
_{4}solution. - Add one test-tube (~ 20 ml) full of dilute sulphuric acid (- 2 M) to the solution in titration flask.
- Note the initial reading of the burette.
- Now add KMnO
_{4}solution from the burette till a permanent light pink colour is imparted to the solution in the titration flask on addition of a last single drop of KMnO_{4}solution. - Note the final reading of the burette.
- Repeat the above steps 4—5 times to get three concordant reading.

**Observations**

Weight of watch glass =……. g

Weight of watch glass + Mohr’s salt =…………..g

Weight of mixture = 3.50 g

Volume of solution prepared = 250 ml

Molarity of KMnO_{4} solution =M/100

Volume of oxalate solution taken for each titration = 20.0 ml.

**Calculations**

Volume of M/100 KMnO_{4} solution required for the oxidation of 20.0 ml of the prepared ferrous sulphate solution = x ml.

From the equations it is clear that 2 moles of KMnO_{4} react with 10 moles of ferrous sulphate.

**Exercises**

- Prepare a standard solution of M/50 FeSO
_{4}(NH_{4})_{2}SO_{4}.6H_{2}0 (Mohr’s salt). Using this solution find out the molarity of the given solution of KMn04. - Prepare M/50 solution of oxalic acid. Using this solution find out the molarity and strength of the given solution of KMnO
_{4}. - Prepare a solution of ferrous ammonium sulphate containing exactly 4.9 g of the salt per 250 ml of solution. Using this solution determine the concentration of KMnO
_{4}in g/litre in the given solution. - Prepare M/20 solution of oxalic acid. Using this solution find out percentage purity of impure sample of KMnO
_{4}, 3.5 g of which have been dissolved per litre. - Prepare M/50 ferrous ammonium sulphate solution. With its help, find out the percentage purity of impure sample of KMnO
_{4}, 3.6 g of which have been dissolved per litre. - Prepare M/20 oxalic acid solution. You are provided two solutions of KMnO
_{4}, A and B. Find out volumetrically which solution, (A or B) is more concentrated. Report the strength of more concentrated solution in g/litre. - You are provided with a solution of alkali metal permanganate, AMn04 containing 3.15 g of it per litre of the solution. Prepare M/20 oxalic acid solution and using this solution determine the atomic mass of the alkali metal ‘A’.
- Determine volumetrically the percentage purity of a given sample of sodium oxalate. Provided M/50 KMnO
_{4}solution.