If I am titrating KMnO4 against a sample of Fe2+, but there is also I- in the sample which of the iron and iodine will be oxidised first?
Unless something is present in the sample to complex the iodide ion, KMnO4 may titrate both. How are you titatrating it? What are you using as an indicator?
I am running in the KMnO4. Basically I want to find concentration Fe2+ in my sample, but there is I- in there too. I was hoping I could use starch as an indicator and that iron would oxidise more readily therefore iodide would only be converted to iodine after the Fe2+ is all used up. Therefore when a blue-black colour after all the iron is gone and this is my end-point.
I don't know anything about the kinetics of the two reactions, but the oxidation postentials for both are in the same range which suggests both might be titrated with KMnO4. I know that titration of iron(II) with KMnO4 is easily done; I don't know of anything to suggest iodide ion might not be oxidized just as easily. Unless this is a "standard procedure" you are using from a text or other reputable reference, I suspect you must so some research to know if what you want to do is feasible.
In order to determine whether iron or iodine will be oxidized first during the titration of KMnO4 against a sample containing Fe2+ and I-, it is important to consider the oxidation potentials of both species.
The oxidation potential is a measure of how easily a species can be oxidized. Generally, the species with a lower oxidation potential will be oxidized first. However, it is also important to consider the reaction kinetics, as some reactions may occur faster than others.
In this case, iron (Fe2+) and iodine (I-) both have oxidation potentials in the same range. Therefore, it suggests that both species could potentially be titrated with KMnO4. The fact that titration of iron(II) with KMnO4 is easily done indicates that Fe2+ will likely be oxidized by KMnO4.
To better understand the feasibility of using starch as an indicator and observing the blue-black color change after all the iron is consumed, it would be beneficial to consult reputable references or conduct further research to determine if there are any complications or interferences from the presence of I- in the sample.