Difference between revisions of "Oxalic acid"

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| Appearance = White hygroscopic crystals
| Appearance = White hygroscopic crystals
| Odor = Odorless
| BoilingPt =  
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Latest revision as of 15:21, 11 January 2020

Oxalic acid
Oxalic acid dihydrate
Oxalic acid structure.png
IUPAC name
Oxalic acid
Systematic IUPAC name
Ethanedioic acid
Other names
1,2-Ethanedioic acid
Wood bleach
Molar mass 90.035 (anhydrous)
126.066 (dihydrate)
Appearance White hygroscopic crystals
Odor Odorless
Density 1.90 g/cm3 (anhydrous)
1.653 g/cm3 (dihydrate)
Melting point 189.5 °C (373.1 °F; 462.6 K) (sublimes)
Boiling point Sublimes
14.3 g/100 ml
Solubility Poorly soluble in acetone, POCl3
Insoluble in benzene, chloroform, petroleum ether, toluene
Solubility in diethyl ether 1.4 g/100 ml (15 °C)
Solubility in ethanol 23.7 g/100 ml (15 °C)
Solubility in formic acid 9.74 g/100 ml (16.8 °C)[1]
Solubility in methanol 27.01 g/100 ml (25 °C)[2]
Vapor pressure 0.001 mmHg (20 °C)
Acidity (pKa) 1.25
-827.5 kJ/mol
Safety data sheet Sigma-Aldrich (anhydrous)
Sigma-Aldrich (dihydrate)
Flash point 166 °C
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Oxalic acid is an organic compound with the chemical formula H2C2O4 or (COOH)2. Along with formic acid, it is one of the most reactive organic acids, but unlike formic acid, pure oxalic acid is solid, non-volatile and can be handled much safer.



Oxalic acid is very strong for an organic acid. It will react with manganese dioxide to form manganese oxalate and carbon dioxide.

MnO2 + 2 H2C2O4 → MnC2O4 + 2 CO2 + 2H2O

Oxalic acid is particularly notable for a number of insoluble salts it forms with common metals, such as magnesium and calcium. Thus, it can be used to displace other acids from these metals' salts, which allows for synthesis of several rare acids.


Oxalic acid is a colorless hygroscopic crystalline solid, with a snow-like aspect. It is soluble in water (143 g/L at 25˚C), more soluble in ethanol (240 g/L) but poorly soluble in ether (18 g/L). It has a weak smell and is irritating to skin. It has a melting point of 102 °C and sublimes between 149 - 160 °C.


Oxalic acid is sometimes available as wood bleach or as beehive disinfecting powder. It can also be bought online, such as from Amazon. "Bar Keepers Friend" is a very cheap multi-surface cleaner containing oxalic acid dihydrate, available at hardware stores.


Oxalic acid can be made from the oxidation of sucrose, glucose, or ethylene glycol using nitric acid or air in the presence of vanadium pentoxide at high temperatures.

Below is a synthesis of oxalic acid found online, using nitric acid and sucrose:

10 g of sugar are added in a flat bottom flask and 50 ml of concentrated nitric acid and heat the flask in a water bath. The reaction will yield nitrogen oxide fumes, so it's best performed outside or in a fume hood. Stop the heating and remove the flask from the water bath. When the reaction subsides, add the hot solution into an evaporating basin. Wash out the flask with 10 ml of conc. nitric acid and evaporate the solution on the water bath until it has a volume of 10 ml. Add 20 ml of water to the solution and evaporate again to 10 ml. Cool the solution in a cooling bath to crystallize the oxalic acid. Dry the crystals.[3]


  • Purifying MnO2 from old batteries
  • Making formic acid by distillation of oxalic acid with glycerol
  • Lanthanide purification
  • Make pyrophoric iron
  • Oxalate esters



Oxalic acid is corrosive to human tissues, so proper protection must be worn. It is not volatile under normal conditions, so its vapors aren't usually a hazard. Oxalates are the notorious cause of kidney stones, so ingestion of both acid and salt should be avoided.


Should be stored in closed bottles.


Oxalic acid and oxalates can be destroyed with hydrogen peroxide.[4]


  1. Aschan; Chemiker-Zeitung, Chemische Apparatur; vol. 37; (1913); p. 1117
  2. Gumtya; Lahiri; Zeitschrift fur Physikalische Chemie; vol. 217; nb. 11; (2003); p. 1341 - 1359
  3. http://www.scribd.com/doc/45869039/preparation-of-Oxalic-acid
  4. http://web.ornl.gov/info/reports/1981/3445605762877.pdf

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