Effect of catalyst and surface area on reaction rate: One of my teachers is doing the above mentioned prac for Yr 11 Chemistry. She has asked for saturated Oxalic acid solution. We don't have this so can you please let me know what else she can use instead. The prac can be found in Prelim Course CD Work Sheet 14 Module 4.
Submitted by sat on 03 October 2016
Answer reviewed 20 February 2023
A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent change. It is not consumed in the reaction.
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 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 few crystals of manganese (II) sulfate.
A substitute for commercial oxalic acid
Note: This reaction is not as straight forward as it may appear, because of competing reactions taking place. The reaction product also acts as a catalyst for the reaction, thereby speeding up the reaction further. This is a process known as autocatalysis.1,2
When manganese dioxide is added to a hydrogen peroxide solution (in water) it catalyses the breakdown of the hydrogen peroxide into water and oxygen gas.
MnO2 + 2H2O2 à MnO2 + 2H2O + O2
The MnO2 acts as a catalyst here. It is chemically unchanged during the course of the reaction. That is why it shows up on both sides of the equation. The hydrogen peroxide is broken down into water (which simply goes into the solution) and gaseous molecular oxygen which bubbles out of solution and into the air.
Hydrogen peroxide is unstable and will slowly decompose over time into oxygen and water. The MnO2 acts as a catalyst to make the reaction occur more rapidly.
Procedure:
Safety notes:
1 Royal Society for Chemistry, (2016), ‘Rates and rhubarb’, Retrieved from the Royal Society for Chemistry website, https://edu.rsc.org/lcredir/learn-chemistry/resource/res00000745/rates-and-rhubarb?cmpid=CMP00005903
2 Polymer properties database, (nd), Autocatalytic reactions, Retrieved (20 February 2023) from the Polymer properties database website: https://www.sciencedaily.com/terms/autocatalysis.htm
3 Chem-Supply. (2020) Hydrogen peroxide 6%, Safety Data Sheet. Search https://shop.chemsupply.com.au/ to source the latest Safety Data Sheet via the product information page.
4 Chem-Supply. (2021). Manganese dioxide Safety Data Sheet. Search https://shop.chemsupply.com.au/ to source the latest Safety Data Sheet via the product information page.
5 LABNETWEST, (2016, October). Manganese dioxide, Retrieved from the LABNETWEST website: http://www.labnetwest.asn.au/manganese-dioxide/