Titration of Oxalic Acid against Sodium Hydroxide

The process of determining the strength of an acid solution by titration with a standard base solution is known as acidimetry. Conversely, when we determine the strength of an alkali solution by titrating it with a standard acid solution, it’s called alkalimetry.

Aim

To find out how strong a sodium hydroxide solution is by titrating it with a standard solution of oxalic acid.

Theory

This experiment involves titrating a weak acid, oxalic acid, with a strong base, sodium hydroxide, using phenolphthalein as an indicator. The reaction between oxalic acid and sodium hydroxide is:

(COOH)₂ + 2NaOH → (COONa)₂ + 2H₂O

Because sodium hydroxide isn’t a primary standard, we prepared a standard solution of oxalic acid for standardizing sodium hydroxide.

In an acid-base titration, at the endpoint, the amount of acid becomes equal to the amount of base, resulting in a neutral solution.

Materials

• Burette
• Pipette
• Conical flask
• Burette stand
• Funnel
• Stirrer
• White glazed tile
• Measuring flask
• Oxalic acid (solid)
• Oxalic acid solution
• Sodium hydroxide solution
• Phenolphthalein indicator

Procedure

(a) Preparing a 0.1M Standard Oxalic Acid Solution:

1. To begin, take a watch glass and clean it with distilled water, ensuring it is completely dry. Then, weigh the watch glass accurately and record its weight in your notebook.
2. Next, measure 3.15 grams of oxalic acid carefully and place it on the watch glass. Record this weight in your notebook as well.
3. Using a funnel, gently transfer the oxalic acid from the watch glass into a clean and dry measuring flask. To remove any remaining particles on the watch glass, rinse it with distilled water, being cautious not to exceed 50 mL of water.
4. Similarly, wash the funnel multiple times with distilled water, ensuring that you use small quantities of water each time, not exceeding 50 mL. This step is essential to move any remaining particles into the measuring flask.
5. Now, rinse the funnel thoroughly with distilled water to ensure that all the solution adhering to it enters the measuring flask.
6. Rotate the measuring flask gently until the oxalic acid fully dissolves.
7. Using a wash bottle, carefully add enough distilled water to the measuring flask, stopping just below the etched mark on the flask.
8. To reach the mark, add the last few mL of distilled water drop by drop into the measuring flask until the reduced meniscus level aligns with the mark.
9. Seal the flask with its stopper and gently shake it to ensure the entire solution is well-mixed. This solution can be considered as a M/10 oxalic acid solution.

(b) Titration of Sodium Hydroxide with Oxalic Acid:

1. Rinse the burette by flushing it with the standard oxalic acid solution.
2. Take 10 milliliters of the oxalic acid solution and place it in a titration flask.
3. Fill the burette with sodium hydroxide solution.
4. Ensure there is no air gap in the burette by forcefully expelling any remaining air from the burette nozzle and make note of the starting measurement.
5. Using a pipette, transfer 20 milliliters of the sodium hydroxide solution into a conical flask, and add 2-3 drops of phenolphthalein indicator.
6. Begin titrating the sodium hydroxide solution with the oxalic acid solution until the pink color disappears.
7. Repeat the titration process until you achieve three consistent readings.

Observations

• Molarity of Oxalic acid solution = M/10
• Sodium hydroxide molarity (N1) = x
• Volume of oxalic acid solution = 10cm³
• Indicator = Phenolphthalein
• End point = Light pink color

Calculations

Mass of Oxalic Acid dissolved in 100ml of standard solution = y g

Strength of Oxalic acid = y x 10g/L

Normality(N) of standard oxalic acid = Strength / Eq. wt = y x 10/63.04 = N

Normality(N1) of Sodium hydorxide solution

N₁ x V₁ = N x V

Therefore, N₁ = N x V/V₁

N₂ = N₁ x V₁/V₂

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

Results

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

Precautions

To weigh the oxalic acid crystals correctly, you will need weights of 2 grams, 1 gram, 100 milligrams, and 50 milligrams.

1. Be careful not to spill any of the substance on the balance pan while weighing.
2. Turn the knob of the balance gently to get an accurate measurement.
3. After weighing, make sure to put the weights back in their proper places in the weights box.
4. When you’re transferring the weighed substance, wash the watch glass thoroughly to ensure no crystals are left behind.
5. Bring the watch glass close to the funnel while transferring the substance and do it gently. Rinse it multiple times with distilled water.
6. After you’ve finished the titration, clean the burette with water.
7. To prevent adding too much distilled water above the mark on the measuring cylinder’s neck, use a pipette for the last few drops.