Titration of Oxalic Acid against Sodium Hydroxide

Table of Content

Aim Theory Apparatus Procedure Observations ResultPrecautions 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 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 is 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 become 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)

Apparatus Setup

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 correctly on the watch glass 3.15 g of oxalic acid 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 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 pink colour disappears.
  6. Repeat the titration till three concordant readings are obtained.

Observations

  1. Molarity of oxalic acid solution = \(\frac{M}{10}\)
  2. Molarity of sodium hydroxide solution = x
  3. Volume of oxalic acid solution = 10cm3
  4. Indicator = Phenolphthalein
  5. End point = Light pink colour
S.No Initial Reading of the Burette Final Reading of the Burette Volume of NaOH solution used Concordant Reading
1 a cm3 b cm3 (b-a) cm3 V cm3
2 b cm3 c cm3 (c-b) cm3 V cm3
3 c cm3 d cm3 (d-c) cm3 V cm3

Calculations

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

Strength of oxalic acid = y \(\times\) 10 g/L

Normality (N) of standard oxalic acid = Strength/ Eq.wt = \(y \times \frac{10}{63.04}\) = N

Normality (N1) of sodium hydroxide solution

N1 \(\times\) V1 = N \(\times\) V

Therefore,

N1 = \(N \times \frac{V}{V_{1}}\)

Normality (N2) of given oxalic acid solution

N2 \(\times\) V2 = N1 \(\times\) V1

N2 = \(N_{1}\times \frac{V_{1}}{V_{2}}\)

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 balance pan.
  3. Rotate the knob of balance gently.
  4. Keep the weights in weights box at 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 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. Last few drops should be added using pipette to avoid extra addition of distilled water above the mark on the neck of the measuring cylinder.


Frequently Asked Questions on Titration of Oxalic Acid against Sodium Hydroxide

What is a standard solution?

Any solution whose strength is known is called a standard solution.

What is a molar solution?

Molar solution is one that contains 1 mole of solute in one litre of solution.

What is acidimetry ?

The method used to determine the strength of an acid by titrating it against a standard alkali solution using suitable indicator is known as acidimetry.

What type of reaction is an acid-alkali titration?

Neutralization titration.

One should not force out the last drop in pipette by blowing. Why?

The volume written on the pipette is the volume of the liquid falls freely. The last drop need not be forced out.

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