Calculate the Percentage of Ions in a Sample of Ferrous Sulphate

Calculate the Percentage of Fe²⁺ 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 KMnO₄

Chemistry Lab ManualNCERT Solutions Class 12 Chemistry Sample Papers

Chemical Equations

Theory
Since the given sample contains partially oxidized ferrous sulphate, it contains both ferrous ions, Fe²⁺ (unoxidised) and ferric ions Fe³⁺ (oxidised). The strength of partially oxidised sample is known. The solution of partially oxidised FeSO₄ of known strength is titrated against standard KMnO₄ solution to determine the molarity and strength of the unoxidised ferrous sulphate. From this the percentage oxidation of the sample can be calculated.

Indicator
KMnO₄ is a self-indicator.

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

Procedure

1. 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.
2. Rinse and fill the burette with the M/100 KMnO₄ 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 a last single drop of KMnO₄ solution.
6. Note the final reading of the burette.
7. 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 KMnO₄ solution =M/100
Volume of oxalate solution taken for each titration = 20.0 ml.

Calculations
Volume of M/100 KMnO₄ 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 KMnO₄ react with 10 moles of ferrous sulphate.

Exercises

1. Prepare a standard solution of M/50 FeSO₄(NH₄)₂SO₄.6H₂0 (Mohr’s salt). Using this solution find out the molarity of the given solution of KMn04.
2. Prepare M/50 solution of oxalic acid. Using this solution find out the molarity and strength of the given solution of KMnO₄.
3. 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 KMnO₄ in g/litre in the given solution.
4. Prepare M/20 solution of oxalic acid. Using this solution find out percentage purity of impure sample of KMnO₄, 3.5 g of which have been dissolved per litre.
5. Prepare M/50 ferrous ammonium sulphate solution. With its help, find out the percentage purity of impure sample of KMnO₄, 3.6 g of which have been dissolved per litre.
6. Prepare M/20 oxalic acid solution. You are provided two solutions of KMnO₄, A and B. Find out volumetrically which solution, (A or B) is more concentrated. Report the strength of more concentrated solution in g/litre.
7. 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’.
8. Determine volumetrically the percentage purity of a given sample of sodium oxalate. Provided M/50 KMnO₄ solution.

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