Class 12 Chemistry Practicals Volumetric Analysis Estimation Of Ferrous Ammonium Sulphate

This Class 12 Chemistry practical record explains the volumetric estimation of Ferrous Ammonium Sulphate (Mohr's salt) by titration with standard ferrous sulphate and potassium permanganate, covering the aim, principle, procedure, observation tables, normality calculations, the weight of FAS in 1500 ml of solution, the result and a short procedure summary.

Ex. No.: 02
2. ESTIMATION OF FERROUS AMMONIUM SULPHATE (FAS) (MOHR'S SALT)
Date:

AIM

To estimate the amount of Ferrous Ammonium Sulphate (FAS) dissolved in 1500 ml of the given unknown solution volumetrically. For this, you are given a standard solution of ferrous sulphate (FeSO₄) of normality 0.1024 N and potassium permanganate solution as the link solution.

PRINCIPLE

During these titrations, Fe²⁺ ions (from ferrous salts) are oxidised to Fe³⁺ ions, and MnO₄^- ions (from KMnO₄) are reduced to Mn²⁺ ions.

Oxidation: 5 Fe²⁺ → 5 Fe³⁺ + 5e^-
Reduction: MnO₄^- + 8H⁺ + 5e^- → Mn²⁺ + 4H₂O
Overall reaction: 5 Fe²⁺ + MnO₄^- + 8H⁺ → 5 Fe³⁺ + Mn²⁺ + 4H₂O

PROCEDURE

Titration I: Standard FeSO₄ versus link KMnO₄
The burette is washed with water, rinsed with KMnO₄ solution and filled with the same KMnO₄ solution up to the zero mark. Exactly 20 ml of the FeSO₄ solution is pipetted out into a clean, washed conical flask. About 20 ml of 2 N H₂SO₄ is added to this solution. The mixture is titrated against the KMnO₄ link solution from the burette. KMnO₄ is added drop by drop until a permanent pale pink colour appears. The burette reading is noted, and the same procedure is repeated to get concordant values.

Titration II: Link KMnO₄ versus unknown FAS
The burette is washed with water, rinsed with KMnO₄ solution and filled with the same KMnO₄ solution up to the zero mark. Exactly 20 ml of the unknown FAS solution is pipetted out into a clean, washed conical flask. About 20 ml of 2 N H₂SO₄ is added to this solution. The mixture is titrated against the KMnO₄ link solution from the burette. KMnO₄ is added drop by drop until a permanent pale pink colour appears. The burette reading is noted, and the same procedure is repeated to get concordant values.

TITRATION II: Link KMnO₄ versus unknown FAS

Indicator: Self (KMnO₄)

CALCULATIONS

Volume of KMnO₄ solution (V₂) = 20.2 ml
Normality of KMnO₄ solution (N₂) = 0.0994 N
Volume of unknown FAS solution (V₃) = 20 ml
Normality of unknown FAS solution (N₃) = ?

By the law of normality, V₂ N₂ = V₃ N₃.
N₃ = (V₂ × N₂) / V₃ = (20.2 × 0.0994) / 20 = 0.10039 N, which is about 0.1004 N.

Normality of unknown FAS solution (N₃) = 0.1004 N.

ESTIMATION: WEIGHT CALCULATION

The amount of FAS dissolved in one litre of the solution = Equivalent weight × Normality.
Equivalent weight of FAS (Mohr's salt) = 392.

The amount of FAS dissolved in 1500 ml of the solution = (Equivalent weight × Normality × 1500) / 1000
= 392 × 0.10039 × 1500 / 1000
= 59.03 g.

The amount of FAS dissolved in 1500 ml of the solution = 59.03 g.

RESULT

1. Normality of KMnO₄ link solution (N₂) = 0.0994 N.
2. Normality of unknown FAS solution (N₃) = 0.1004 N.
3. The amount of FAS dissolved in 1500 ml of the solution = 59.03 g.

SHORT PROCEDURE

Normality of standard ferrous ammonium sulphate (FAS) solution = 0.1 N

TITRATION I: Standard FAS versus link KMnO₄

Indicator: Self (KMnO₄)

CALCULATIONS

Volume of standard FAS solution (V₁) = 20 ml
Normality of standard FAS solution (N₁) = 0.1 N
Volume of KMnO₄ link solution (V₂) = 20.4 ml
Normality of KMnO₄ link solution (N₂) = ?

By the law of normality, V₁ N₁ = V₂ N₂.
N₂ = (V₁ × N₁) / V₂ = (20 × 0.1) / 20.4 = 0.0980 N.

Normality of KMnO₄ link solution (N₂) = 0.0980 N.