Class 12 Chemistry Practicals Volumetric Analysis Estimation Of Oxalic Acid

This Class 12 Chemistry practical record explains the volumetric estimation of oxalic acid by titrating it against a link sodium hydroxide solution with phenolphthalein indicator. It covers the aim, principle, neutralisation equations, both titration procedures, the concordant readings, the normality and weight calculations for 1250 ml of the unknown solution, and the result.

5. ESTIMATION OF OXALIC ACID

Ex. No: 04.
Date:

AIM

To estimate the amount of oxalic acid dissolved in 1250 ml of the given unknown solution volumetrically. For this you are given a standard solution of HCl of normality 0.1010 N and sodium hydroxide solution as link solution.

PRINCIPLE

1. Neutralisation of sodium hydroxide by HCl is given below. To indicate the end point, phenolphthalein is used as an indicator.

NaOH + HCl → NaCl + H₂O

2. Neutralisation of sodium hydroxide by oxalic acid is given below. To indicate the end point, phenolphthalein is used as an indicator.

2NaOH + (COOH)₂ → (COONa)₂ + 2H₂O

PROCEDURE

Titration I: (Std HCl) Vs (Link NaOH)

The burette is washed with water, rinsed with link HCl solution and filled with the same HCl solution up to the zero mark. Exactly 20 ml of NaOH solution is pipetted out into a clean, washed conical flask. To this solution 2 to 3 drops of phenolphthalein indicator are added and titrated against the HCl solution from the burette. HCl is added drop wise till the pink colour disappears completely. The burette reading is noted and the same procedure is repeated to get concordant values.

Titration II: (Link NaOH) Vs (Unknown Oxalic acid)

The burette is washed with water, rinsed with oxalic acid solution and filled with the same oxalic acid solution up to the zero mark. Exactly 20 ml of NaOH solution is pipetted out into a clean, washed conical flask. To this solution 2 to 3 drops of phenolphthalein indicator are added and titrated against the oxalic acid solution from the burette. Oxalic acid is added drop wise till the pink colour disappears completely. The burette reading is noted and the same procedure is repeated to get concordant values.

TITRATION II: (Link NaOH) Vs (Unknown Oxalic acid)
Indicator: Phenolphthalein

CALCULATIONS

Volume of NaOH link solution (V₂) = 20 ml
Normality of NaOH link solution (N₂) = 0.1035 N
Volume of unknown oxalic acid solution (V₃) = 19.7 ml
Normality of unknown oxalic acid solution (N₃) = ? N

According to the normality equation: V₂N₂ = V₃N₃

1. N₃ = \( \frac{V_2 N_2}{V_3} = \frac{20 \times 0.1035}{19.7} \) = 0.1050 N
2. Normality of unknown oxalic acid solution (N₃) = 0.1050 N

ESTIMATION: WEIGHT CALCULATION

1. Amount of oxalic acid dissolved in one litre of the solution = Equivalent weight × Normality
2. Equivalent weight of oxalic acid = 63
3. Amount of oxalic acid dissolved in 1250 ml of the solution = \( \frac{\text{Equivalent weight} \times \text{Normality} \times 1250}{1000} \)
4. = 0.1050 × 63 × 5 / 4 = 8.26 g

Amount of oxalic acid dissolved in 1250 ml of the solution = 8.27 g.

Note: The working above gives 8.26 g, which is rounded to 8.27 g in the final answer.

RESULT

1. Normality of NaOH link solution = 0.1035 N
2. Normality of oxalic acid solution = 0.1050 N
3. Amount of oxalic acid dissolved in 1250 ml of the solution = 8.27 g