How to Make Oxalic Acid

Written by allan robinson
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Oxalic acid (H2C2O4) is a relatively strong organic acid and is a common reducing agent in organic chemistry. There are a number of methods for preparing oxalic acid from nitric acid, and one important difference among them is the amount of oxalic acid that is produced from a given amount of nitric acid. Oxalic acid can be prepared in a laboratory with nothing more than sugar and nitric acid, although a small amount of vanadium pentoxide will act as a catalyst and allow the reaction to proceed much more swiftly.

Skill level:
Moderate

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Things you need

  • 100ml nitric acid
  • 20g cane sugar
  • 750ml flat-bottomed flask
  • Bunsen burner
  • Drying paper or desiccator
  • Evaporating basin
  • Filter paper
  • Large container to hold boiling water

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Instructions

  1. 1

    Place the sugar in the flat-bottomed flask and add the nitric acid. Heat the flask in a bath of boiling water. The sugar will dissolve in a vigorous reaction that produces an extremely large amount of nitric acid fumes.

  2. 2

    Remove the flask from the water bath as soon as the reaction begins to produce the fumes, and place it on a surface that will not conduct heat. After the reaction subsides in about 15 minutes, pour the still-hot solution into an evaporating basin.

  3. 3

    Evaporate the solution with mild heat from a Bunsen burner for about 15 minutes until it reaches a volume of about 20ml, then add about 40ml of water. Evaporate the solution down to about 20ml again, and thoroughly cool the solution in an ice-water bath.

  4. 4

    Allow the rapidly forming crystals of oxalic acid to complete their crystallisation in about 10 minutes. Filter the remaining solution through filter paper, and add the crystals to a small amount of hot water. Allow the oxalic acid to recrystallize, which should take about 20 minutes.

  5. 5

    Dry the crystals by pressing them between pads of drying paper or with a desiccator. Don't use an ordinary oven since this could cause the oxalic acid to decrystallize. This preparation should yield about 7g of oxalic acid.

Tips and warnings

  • This method will produce a large amount of nitric acid fumes and must be performed under a fume hood with adequate ventilation.

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