Preparation and standardization of oxalic acid using sodium hydroxide

Learn about the determination of the concentration (strength) of a given sodium hydroxide solution by titrating it against a standard solution of oxalic acid through a laboratory experiment or practical.

Aim:

Determination of the concentration (strength) of a given sodium hydroxide solution by titrating it against a standard solution of oxalic.

Requirements:

Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, wash bottle, etc.

Chemicals: LR grade oxalic acid (C2H2O4), sodium hydroxide (NaOH), phenolphthalein indicator, etc.

Apparatus: Digital/analytical balance

Theory:

It is based on alkalimetry titration, at the point in the titration of a strong acid with a strong base, the amount of acid and base becomes chemically equivalent, and the chemical reaction is referred to as a neutralization reaction.

The pH of the solution suddenly changes near the end point. Even a small volume of base or acid added after the end point would become slightly alkaline or acidic respectively. When oxalic acid (a weak acid) is titrated with sodium hydroxide (a strong base), the following reaction happens:

In this titration the endpoint is detected using the phenolphthalein HPh indicator.

Preparation of 0.1M oxalic acid solution:

Weigh accurately 12.67 gm of oxalic acid and add 500 ml of distilled water. Once it has completely dissolved, make up the volume to 1000 ml.

Titration procedure:

• All glassware should be cleaned and dried according to standard laboratory procedures.
• Before filling the burette for the titration, rinse it with distilled water and then pre-rinse it with a portion of the titrant solution. Pre-rinsing is required to make sure that all solution in the burette is the desired solution, not a contaminated or diluted solution.
• Take the unknown stock solution of titrant in a clean and dry beaker then fill the burette using the funnel.
• Remove air bubbles from the burette and adjust the reading to zero.
• Take 10.00 ml of prepared 10 mL of oxalic acid solution and pour it into a conical flask.
• Add 2-3 drops of phenolphthalein indicator.
• Titrate the acid with sodium hydroxide solution (NaOH) till a very faint permanent pink colour is obtained.
• Properly record the readings of the burette.
• To get accurate results, repeat the titration three times.
• The following equation can be used to determine the molarity of a NaOH solution.

Observation table:

Sr. No.	Content in conical flask	Burette reading		Volume of titrant used (ml)
		Initial	Final
1
2
3
				Mean:

Calculations:

a1 M1V1 = a2 M2V2

where M1 and V1 are the molarity and volume of the oxalic acid solution.

M2 and V2 are the molarity and volume of the sodium hydroxide solution.

 

Result:

The strength of the prepared NaOH solution was found to be_____M.

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