What is the relationship between the surface area of rhubarb and how fast it decolorises potassium permanganate?

Expert Answers
gsenviro eNotes educator| Certified Educator

Rhubarb is a plant that contains oxalic acid. A common laboratory experiment for school students is the decoloration of potassium permanganate solution through the addition of rhubarb. When we add stalks of rhubarb, the purple color of potassium permanganate solution disappears because the oxalic acid reduces the manganate ion. In this experiment, students are taught the relationship between the surface area of rhubarb and rate of decoloration of the solution. Higher surface area results in faster disappearance of color.

One way to check this is by using increasing amounts of rhubarb stalks (of equal length) in different containers containing the same amount of potassium permanganate solution and measuring the time taken for decoloration. More rhubarb stalks will cause faster decoloration.

A mathematical relationship between the surface area of rhubarb and rate of decoloration is a function of the oxalic acid content of the particular stalk we are using. Thus, it would be difficult to determine an exact and generalized relationship. However, we can simply observe that increasing the surface area of rhubarb will reduce the time taken to decolorize the solution. In other words, surface area is proportional to the rate of decoloration.

Hope this helps.