Titration of Oxalic Acid against Sodium Hydroxide

Table of Content

• Aim
• Theory
• Procedure
• Observations
• Result
• Precautions
• Viva-Voce

The determination of the strength of a solution of an acid by titration with a standard solution of a base is called acidimetry, whereas when the strength of a solution of an alkali is determined by means of titration with standard solution of an acid, it is termed as alkalimetry.

Aim

To determine the strength of a given solution of sodium hydroxide solution by titrating it against a standard solution of oxalic acid.

Theory

This estimation involves titration of a weak acid that is oxalic acid against a strong base sodium hydroxide and phenolphthalein is the indicator of choice. The reaction between oxalic acid and sodium hydroxide is

(COOH)₂ + 2NaOH → (COONa)₂ + 2H₂O

Since sodium hydroxide is not a primary standard a standard solution of oxalic acid is prepared and used for standardisation of sodium hydroxide.

In acid-base titration at the end point the amount of acid becomes chemically equivalent to the amount of base present. In case of strong acid and strong base titration at the end point of solution the solution becomes neutral.

Materials Required

1. Burette
2. Pipette
3. Conical flask
4. Burette stand
5. Funnel
6. Stirrer
7. White glazed tile
8. Measuring flask
9. Oxalic acid (solid)
10. Oxalic acid (as per needed)
11. Sodium hydroxide solution (as per needed)
12. Phenolphthalein indicator (as per needed)

Procedure

(a) Preparation of 0.1M Standard Oxalic Acid Solution

1. Take a watch glass, wash it with distilled water and dry it.
2. Weigh the exact amount of clean and dried watch glass and record its weight in the notebook.
3. Weigh 3.15 g of oxalic acid on the watch glass correctly and record this weight in the notebook.
4. Using a funnel, transfer oxalic acid softly and carefully from the watch glass into a clean and dry measuring flask.
5. Wash the watch glass with distilled water to move the particles that stick to it into the foam with the assistance of a wash bottle.
6. For this purpose, the volume of distilled water should not exceed 50 ml.
7. Wash the funnel several times with distilled water to move the sticking particles into the measuring flask using a wash bottle. Add water in tiny quantities while washing the funnel. The distilled water quantity used for this purpose should not exceed 50 mL.
8. Using a wash bottle, wash the funnel carefully with distilled water to pass the solution attached to the funnel into the measuring flask
9. Turn the flask of measurement until the oxalic acid dissolves.
10. Using a wash bottle, thoroughly add enough distilled water to the measuring flask just below the etched mark on it.
11. Add the last few mL of distilled water drop into the measuring flask until the reduced meniscus level just touches the mark.
12. Put the stopper on the mouth of the flask and shake softly to make the entire solution uniform. Calculate it as a solution of oxalic acid M/10.

(b) Titration of Sodium Hydroxide and Oxalic Acid Solution

1. Rinse the burette with the standard oxalic acid solution.
2. Take 10cm³ of oxalic acid solution in a titration flask. Fill the burette with sodium hydroxide solution.
3. Remove the air gap if any, from the burette by running the solution forcefully from the burette nozzle and note the initial reading
4. Pipette out 20ml of NaOH solution is a conical flask. Add 2-3 drops of phenolphthalein indicator to it.
5. Titrate the base with oxalic acid solution until the pink colour disappears.
6. Repeat the titration till three concordant readings are obtained.

Observations

1. \(\begin{array}{l}Molarity\ of\ oxalic\ acid\ solution = \frac{M}{10}\end{array} \)
2. Molarity of sodium hydroxide solution = x
3. Volume of oxalic acid solution = 10cm³
4. Indicator = Phenolphthalein
5. End point = Light pink colour

Calculations

Mass of oxalic acid dissolved in 100ml of standard solution = y g

Normality (N₁) of sodium hydroxide solution

Therefore,

Normality (N₂) of given oxalic acid solution

Strength of given oxalic acid = N₂ x 63.04 g/L

Results and Discussion

The strength of the given sodium hydroxide solution is _______ g/L.

Precautions

1. Weighing of oxalic acid crystals need weights of 2g + 1g + 100mg + 50mg.
2. While weighing, do not spill the substance on the balance pan.
3. Rotate the knob of balance gently.
4. Keep the weights in the weights box at the proper places after weighing
5. Wash the watch glass carefully so that even a single crystal is not left on the watch glass.
6. Bring the watch glass close to the funnel while transferring weighed substance and transfer it gently. Wash it repeatedly with distilled water.
7. Wash the burette with water after titration is over.
8. The last few drops should be added using a pipette to avoid extra addition of distilled water above the mark on the neck of the measuring cylinder.