The key difference between iodometry and iodimetry is that we can use Iodometry to quantify oxidizing agents, whereas we can use iodimetry to quantify reducing agents.
Iodometry and iodimetry are two common titration methods useful in analytical chemistry. The basis of these two types of titrations is oxidation-reduction, and we can use it to determine redox species quantitatively. The basis of titration is a reaction between the analyte and a standard reagent known as the titrant. We can determine the quantity of the analyte if we know the reaction, stoichiometry and the volume/mass of the titrant needed to react completely with the analyte. Moreover, we can use iodine for this redox titrations due to its capability of reacting fast with many species. Reversibility of iodine/iodide, the reaction is also an advantage when using them in iodometric reactions.
What is Iodometry?
In iodometry, iodides react with another oxidizing agent in an acidic medium or neutral medium. When this reaction takes place, iodide (we add iodide in the form of KI) oxidizes to iodine and the other species will undergo reduction by iodide. Then we can titrate the released iodine with another species. This titrating species is a standard solution of a reducing agent, which is capable of reducing iodine back to iodide form. Usually, we use a standard thiosulphate solution for this. For example, if we want to quantify the amount of chlorine dissolved in a mixture, the following is the method to carry out an iodometric titration.
First, we should take a known amount of volume from the mixture (in which chlorine is dissolved) into a titration flask. Then we can titrate it with a known solution of KI, and we can find the volume consumed.
Following the redox reaction will take place in the reaction flask;
Cl2 + 2I– —> 2 Cl– + I2
Then we should carry out another titration with the same mixture to determine the released amount of iodine. For this, we can titrate the mixture with a standard thiosulphate solution. We need to add starch as an indicator, to determine the end point of this reaction. With iodine and starch in the mixture, it will appear in dark-blue colour, but at the end point when all the iodine is finished, the dark colour will disappear.
I2 + 2 S2O32− → S4O62− + 2 I–
From the above two titrations, we can determine the amount of Cl2.
What is Iodimetry?
In iodimetry, it uses free iodine to undergo titration with a reducing agent. Therefore, iodine reduces to iodide, and iodine will oxidize other species.
Since we cannot easily prepare a free iodine solution, we have to mix iodine with potassium iodide and KI3 solution to prepare the required solution. And a standard solution of this is used for the iodometric titrations.
KI+I2 → KI3
Following reaction takes place when titrating. We can use starch as an indicator for iodometric titrations too.
I2 + reducing agent → 2 I–
What is the Difference Between Iodometry and Iodimetry?
Iodometry is the quantitative analysis of a solution of an oxidizing agent by adding an iodide that reacts to form iodine, which is then titrated whereas iodimetry is a volumetric analysis involving either titration with a standardized solution of iodine, or the release by a substance under examination of iodine in soluble form, so that we can determine its concentration by titration. This is one difference between iodometry and iodimetry.
Furthermore, another difference between iodometry and iodimetry is that, in iodometry, iodides react with another oxidizing agent in an acidic medium or neutral medium while in iodimetry, it uses free iodine to undergo titration with a reducing agent.
The below infographic presents the difference between iodometry and iodimetry in tabular form.
Summary – Iodometry vs Iodimetry
Although the two terms iodometry and iodimetry sound similar, they are two different techniques we use in analytical chemistry. The key difference between iodometry and iodimetry is that we can use Iodometry to quantify oxidizing agents, whereas we can use iodimetry to quantify reducing agents.
1. “Iodometry.” Wikipedia, Wikimedia Foundation, 9 Sept. 2018. Available here
2. Naviglio, Daniele. “Iodometry and Iodimetry, Daniele Naviglio « Analytical Chemistry « Agraria « Federica e-Learning.” Federica, Federica Web Learning, Università Di Napoli Federico II, 20 Mar. 2012. Available here