The reaction between acidified potassium permanganate and oxalic acid is a common redox reaction used to explain the effect of catalyst on the rate of reaction. During the reaction autocatalysis occurs and the purple pink potassium permanganate solution (MnO4-) is reduced to a colourless solution of manganese ions (Mn2+). The catalyst used for this reaction is usually a saturated solution or a few crystals of manganese (II) sulfate.
There are a number of substitutes for oxalic acid:
- Rhubarb contains oxalic acid. Fresh or frozen rhubarb sticks can be used with acidified potassium permanganate to explain both effect of catalysis and surface area on the rate of reaction. Here is a link to a method using rhubarb: Rates and rhubarb
- Many other vegetables contain oxalic acid, see: Oxalic Acid Content of Selected Vegetables
- Glucose: an aqueous solution of glucose can be used as reducing agent. Glucose will reduce the acidified potassium permanganate solution and the colour will change from purple pink to colourless. Here is a link to an activity using glucose: Estimating glucose concentration in solution.
- You may need to trial the concentration of the oxalic acid substitute required to be used in your activity.
Science ASSIST recommendations:
- A site-specific risk assessment should be conducted
- Suitable PPE such as laboratory coat, closed in shoes and safety glasses should be worn at all times
- Sulfuric acid is corrosive; causes severe skin burns and eye damages.
- Oxalic acid is corrosive and toxic, harmful in contact with skin and if swallowed. Can cause serious eye damage as well.
Note: Potassium permanganate solution is harmful to aquatic life with long lasting effects. For potassium permanganate disposal, see previously answered questions
Aqueous solutions of both oxalic acid and glucose can reduce aqueous potassium permanganate solution in the presence of sulfuric acid.
The chemical equation for the reaction between oxalic acid and potassium permanganate is:
2 MnO4- (aq) + 5 H2C2O4 (aq) + 6 H+(aq) → 2Mn2+(aq) + 10 CO2 (aq) + 8 H2O (l)
Rhubarb leaves are poisonous due to high concentration of oxalic acid and the possibility of anthraquinone glycosides. Rhubarb poisoning occurs when someone consumes the leaves from a rhubarb plant.
'Autocatalysis', Science daily website, https://www.sciencedaily.com/terms/autocatalysis.htm (Accessed October 2016)
'Estimating glucose concentration in solution', Science and Plants for Schools website, http://www.saps.org.uk/attachments/article/103/SAPS%20-%20Estimating%20glucose%20concentration%20in%20solution%20-%20Scottish%20Highers.pdf (Accessed October 2016)
‘Oxalic Acid Content of Selected Vegetables’, United States Department of Agriculture website, https://web.archive.org/web/20170206160415/https://www.ars.usda.gov/nort... (The original page no longer exists, this copy provided ny the Internet Archives Wayback Machine, March 2018).
‘Oxalic acid, Safety Data sheet, Chem-Supply website, https://www.chemsupply.com.au/documents/OA0071CH4U.pdf (March 2015)
‘Potassium permanganate’, Safety Data sheet, Chem-Supply website, https://www.chemsupply.com.au/documents/PL0031CH5L.pdf (August 2016)
'Rates and rhubarb', Royal Society for Chemistry website, http://www.rsc.org/learn-chemistry/resource/res00000745/rates-and-rhubarb?cmpid=CMP00005903 (2016)
'Rhubarb leaves poisoning', U.S. National Library of Medicine website, https://medlineplus.gov/ency/article/002876.htm (Accessed October 2016)
‘Sulphuric acid’, Safety Data sheet, Chem-Supply website, https://www.chemsupply.com.au/documents/SA0081CH72.pdf (April 2013)