Estimation of oxalic acid

Estimation of oxalic acid

Aim :

To estimate the amount of oxalic acid dissolved in 500 ml of the given solution volumetrically. For this you are given with a standard solution of ferrous ammonium sulphate (FAS) of normality 0.1 N and potassium permanganate solution as link solution.

Principle:

During these titrations, oxalic acid is oxidized to CO₂ and MnO₄- ions (from KMnO₄ ) is reduced to Mn²⁺ ion.

Oxidation  : MnO ⁻ + 8H⁺  + 5e⁻     →  Mn²⁺ + 4H O 

Reduction : 

Overall reaction

5(COOH)₂ + 2MnO₄ ⁻ + 6H⁺     → 10CO₂ + 2Mn²⁺ + 8H₂O

Since one mole oxalic acid releases 2 moles of electrons, the equivalent weight of oxalic acid = 106/2 = 63 (oxalic acid is dihydrated)

Short procedure:

Procedure :

Titration–I

(Link KMnO₄)Vs (Standard FAS )

Burette is washed with water, rinsed with KMnO₄ solution and filled with same KMnO₄ solution up to the zero mark. Exactly 20 ml of standard FAS solution is pipetted out into the clean, washed conical flask. To this FAS solution, approximately 20ml of 2N sulphuric acid is added. This mixture is titrated against KMnO₄ Link solution from the burette. KMnO₄ is added drop wise till the appearance of permanent pale pink colour. Burette reading is noted and the same procedure is repeated to get concordant values.

Titration –I

(Link KMnO₄ )Vs (Standard FAS solution)

Calculation :

Volume of KMnO₄ (link) solution V₁ = ml

Normality KMnO₄ (link) solution N₁ = ? N

Volume of standard FAS solution V₂ = 20 ml

Normality of standard FAS solution N₂ = 0.1 N

According to normality equation:

V₁ x N₁ = V₂ x N₂

N₁ = V₂ x N₂ / V₁  =

Normality KMnO₄ (link) solution N₁ = ____________ N

Titration–II

(Unknown oxalic acid ) Vs (Link KMnO₄ )

Burette is washed with water, rinsed with KMnO₄ solution and filled with same KMnO₄ solution up to the zero mark. Exactly 20 ml of unknown oxalic acid solution is pipetted out into the clean, washed conical flask. To this oxalic acid solution approximately 20ml of 2N sulphuric acid is added. This mixture is heated to 60 – 700C using Bunsen burner and that hot solution is titrated against KMnO₄ Link solution from the burette. KMnO₄ is added drop wise till the appearance of permanent pale pink colour. Burette reading are noted, the same procedure is repeated to get concordant values.

Titration –II

(Link KMnO₄ )Vs (Unknown oxalic acid)

Calculation :

Volume of Unknown oxalic acid solution V₁ = 20 ml

Normality of Unknown oxalic acid solution N₁ = ? N

Volume of KMnO₄ (link) solution V₂ = ml

Normality KMnO₄ (link) solution N₂ = N

According to normality equation:

 V₁ x N₁ = V₂ x N₂

N₁ = V₂ x N₂ /  V₁

Normality of Unknown oxalic acid solution N1 = ________ Y _______ N

Weight calculation:

The amount of oxalic acid dissolved in 1 lit of the solution  =(Normality) x (equivalent weight)

The amount of oxalic acid dissolved in 500 ml of the solution  = [Y × 63 × 500] /  1000

 =  [ ? x 63 x 500] / 1000

 = ____ g

Report :

The amount of oxalic acid dissolved in 500 ml of given the solution = g