what is the purple thing on the potassium iodine and starch paper.

[sarahbbbbbb]

I am using the potassium iodide and starch paper to detect the oxidiser agent in the solution. I dipped a drop of my solution on the paper and the central of the drop is clean and the edge of the drop has turned brown/purple.

Please can anyone give me an idea why???

[naita]

@sarahbbbbbb

I am using the potassium iodide and starch paper to detect the oxidiser agent in the solution. I dipped a drop of my solution on the paper and the central of the drop is clean and the edge of the drop has turned brown/purple.

Please can anyone give me an idea why???

This sounds a lot like homework help, and unfortunately that’s not a thing we do here. If it’s not school work, please tell us why you are doing this.

[Ynnad]

I have seen something similar when using potassium iodide and starch paper to test for the presence of oxidizers in unknowns. It seems to happen when the oxidizer turns out to be an extremely powerful oxidizer. I guess that it is because the oxidizer oxidizes the iodide ion beyond iodine and turns it into something like an iodate ion which is colorless with starch. A little iodine and blue color might remain around the edges if you are lucky. If you watch it react, you will see a dark blue color at first but then it fades. If you have technicians screening hundreds and hundreds of samples per day, you need to caution them to be on the lookout for these types of samples. They might miss the initial color change, come back later and see the white paper, and declare the result negative for the presence of oxidizers. And that particular sample might contain an extremely powerful oxidizer that you really need to be concerned about.

[sarahbbbbbb]

@naita

This sounds a lot like homework help, and unfortunately that’s not a thing we do here. If it’s not school work, please tell us why you are doing this.

lol, it is not a school work for sure.:smack: I am putting BPO (benzoyl peroxide) in sodium hydroxide and after a few hours stirring in warm temperature. I used starch paper to test and it was how it look…

[sarahbbbbbb]

@Ynnad

I have seen something similar when using potassium iodide and starch paper to test for the presence of oxidizers in unknowns. It seems to happen when the oxidizer turns out to be an extremely powerful oxidizer. I guess that it is because the oxidizer oxidizes the iodide ion beyond iodine and turns it into something like an iodate ion which is colorless with starch. A little iodine and blue color might remain around the edges if you are lucky. If you watch it react, you will see a dark blue color at first but then it fades. If you have technicians screening hundreds and hundreds of samples per day, you need to caution them to be on the lookout for these types of samples. They might miss the initial color change, come back later and see the white paper, and declare the result negative for the presence of oxidizers. And that particular sample might contain an extremely powerful oxidizer that you really need to be concerned about.

If that is the case then, after a reduction reaction i shall see the starch paper in colour?

[Ynnad]

@sarahbbbbbb

If that is the case then, after a reduction reaction i shall see the starch paper in colour?

Only if you are able to reduce only back to iodine and not reduce it all the way back to iodide. And even then maybe not. Iodine tends to combine with iodide ions to form what is called the triiodide ion. It is actually the triiodide ion that forms a blue complex with starch, not the iodine by itself. If there are no iodide ions left in your system, you will never get the triiodide ions you need to see the color.

[purplehorseshoe]

Total lay here: are you saying that some substances are such powerful oxidizers that they “overload” the test paper? Like turning up the volume so loud you blow out the speakers?

[Ynnad]

@purplehorseshoe

Total lay here: are you saying that some substances are such powerful oxidizers that they “overload” the test paper? Like turning up the volume so loud you blow out the speakers?

Yes.