# How to determine which radicals are dominant in oxidation

I'm looking at the oxidation of I- ions by OH radicals to form iodine and finally triiodide.

This is a well known method of dosimetry, however some consider it flawed because during disassociation of solution other radicals are produced such as H or O radicals. They could also potentially oxidise the I- ions.

How would I show that the oxidation is caused primarily by the OH radicals?

TeethWhitener
Gold Member
It sounds like you’re trying to describe iodometric titration, where you use an iodide solution to titrate a sample with an unknown amount of oxidant. The titration itself is not particularly sensitive to the type of oxidant. In fact, iodometric titration is usually used to measure H2O2 in solution. So I don’t think this is the best way to directly measure OH radicals. EPR might be a better bet.

Also, (brief aside) unless you’re inside the cooling water of a nuclear reactor, it’s exceedingly unlikely that free O or H atoms will be produced in solution. In fact, there’s a sizeable debate as to whether OH radicals are actually formed in solution. For example, in the Fenton reaction, which supposedly generates OH radicals transiently from hydrogen peroxide, there is some evidence that the oxidant is a hard-to-isolate oxo-iron open shell species.

rwooduk
It sounds like you’re trying to describe iodometric titration, where you use an iodide solution to titrate a sample with an unknown amount of oxidant. The titration itself is not particularly sensitive to the type of oxidant. In fact, iodometric titration is usually used to measure H2O2 in solution. So I don’t think this is the best way to directly measure OH radicals. EPR might be a better bet.

Also, (brief aside) unless you’re inside the cooling water of a nuclear reactor, it’s exceedingly unlikely that free O or H atoms will be produced in solution. In fact, there’s a sizeable debate as to whether OH radicals are actually formed in solution. For example, in the Fenton reaction, which supposedly generates OH radicals transiently from hydrogen peroxide, there is some evidence that the oxidant is a hard-to-isolate oxo-iron open shell species.

Many thanks and apologies for the later reply. The process is ultrasonic cavitation whereby ultrasound incident upon a solution causes cavities and the change in pressure causes them to expand and collapse. The result is dissassociation and / or ionisation of the solution / soultion vapour that has entered the cavities via rectified diffusion. Radicals are produced. We determine the sonochemical "efficiency" or the production of OH radicals in KI solution by testing for triiodide (and infer this represents H2O2 production).

Some say this is unreliable as other radicals can oxidise the I- ions.

Thanks for your reply! From the sounds of it you agree that this is not an accurate method for determination of OH radicals.

Apologies for the delay in reply and I would welcome any more comments.