Class 12 Chemistry Practicals Volumetric Analysis Estimation of Ferrous Sulphate

This Class 12 Chemistry practical record explains the volumetric estimation of ferrous sulphate (FeSO₄) by titrating it against potassium permanganate (KMnO₄) solution, which acts as a self indicator. It covers the aim, the redox principle with ionic equations, the short procedure, both titrations with their readings, the normality and weight calculations for 750 ml of the unknown solution, and the result.

VOLUMETRIC ANALYSIS

1. ESTIMATION OF FERROUS SULPHATE (FeSO₄)

Ex. No: 1.
Date:

AIM

To estimate the amount of ferrous sulphate dissolved in 750 ml of the given unknown solution volumetrically. For this you are given a standard solution of ferrous ammonium sulphate (FAS) of normality 0.1102 N and potassium permanganate solution as link solution.

PRINCIPLE

1. During these titrations, Fe²⁺ ions (from ferrous salts) are oxidised to Fe³⁺ ions and MnO₄^- ions (from Mn²⁺) are reduced to Mn²⁺ ions.
2. Oxidation: 5Fe²⁺ → 5Fe³⁺ + 5e^-
3. Reduction: MnO₄^- + 8H⁺ + 5e^- → Mn²⁺ + 4H₂O
4. Overall reaction: 5Fe²⁺ + MnO₄^- + 8H⁺ → 5Fe³⁺ + Mn²⁺ + 4H₂O

PROCEDURE

Titration I: (Std FAS) Vs (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 standard FAS solution is pipetted out into a clean, washed conical flask. To this FAS solution, approximately 20 ml of 2N H₂SO₄ is added. This mixture is titrated against the KMnO₄ link solution from the burette. KMnO₄ is added drop wise till the appearance of a permanent pale pink colour. The burette reading is noted, and the same procedure is repeated to get concordant values.

Titration II: (Link KMnO₄) Vs (Unknown FeSO₄)

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 unknown FeSO₄ solution is pipetted out into a clean, washed conical flask. To this FeSO₄ solution, approximately 20 ml of 2N H₂SO₄ is added. This mixture is titrated against the KMnO₄ link solution from the burette. KMnO₄ is added drop wise till the appearance of a permanent pale pink colour. The burette reading is noted and the same procedure is repeated to get concordant values.

SHORT PROCEDURE

Normality of Ferrous Sulphate (FeSO₄) solution = 0.1024 N

TITRATION I: Std FAS Vs Link KMnO₄
Indicator: Self (KMnO₄)

CALCULATIONS FOR TITRATION I

Volume of standard FAS solution (V₁) = 20 ml
Normality of standard FAS solution (N₁) = 0.1102 N
Volume of KMnO₄ link solution (V₂) = 20.6 ml
Normality of KMnO₄ link solution (N₂) = ? N

According to the law of normality: V₁N₁ = V₂N₂

1. N₂ = \( \frac{V_1 N_1}{V_2} \) = \( \frac{20 \times 0.1024}{20.6} \)
2. N₂ = 0.1070 N (rounded to four decimal places)

Normality of KMnO₄ link solution (N₂) = 0.1070 N.

TITRATION II: Link KMnO₄ Vs Unknown FeSO₄
Indicator: Self (KMnO₄)

CALCULATIONS FOR TITRATION II

Volume of KMnO₄ link solution (V₂) = 20.6 ml
Normality of KMnO₄ link solution (N₂) = 0.1070 N
Volume of unknown FeSO₄ solution (V₃) = 20 ml
Normality of unknown FeSO₄ solution (N₃) = ? N

According to the normality equation: V₂N₂ = V₃N₃

1. N₃ = \( \frac{V_2 N_2}{V_3} \) = \( \frac{20.6 \times 0.1130}{20} \)
2. N₃ = 0.1102 N

Normality of unknown FeSO₄ solution (N₃) = 0.1102 N.

Note: The printed record gives the link KMnO₄ normality as 0.1130 N and the unknown as 0.1163 N,

ESTIMATION: WEIGHT CALCULATION

1. Amount of FeSO₄ dissolved in one litre of the solution = Equivalent weight × Normality
2. Equivalent weight of FeSO₄·7H₂O = 278
3. Amount of FeSO₄ dissolved in 750 ml of the solution = \( \frac{\text{Equivalent weight} \times \text{Normality} \times 750}{1000} \)
4. = \( \frac{278 \times 0.1163 \times 750}{1000} \) = \( 0.1163 \times 278 \times \frac{3}{4} \) = 24.24 g

Amount of FeSO₄ dissolved in 750 ml of the solution = 24.24 g.

RESULT