Iodine Precipitate

[dubois928]

When I burned a few drops of Iodine Tincture on a thin piece of aluminum, a very minute amount of light gray-brown powder was left. What is it?

 

Thanks,

Kenneth Anderson

[Melvin]

It could be aluminum triiodide. If its pure, it would be colorless, but small impurities will make it brown.

[YT2095]

also Iodine tincture is made with KI also, the ions from that help with the solvation of the I2.

[Melvin]

I read somewhere that elemental iodine can be produced from copper(II) sulfate and potassium iodide. Would aluminum iodide work in place of KI? What about FeI2?

[vampares]

When I burned a few drops of Iodine Tincture on a thin piece of aluminum, a very minute amount of light gray-brown powder was left. What is it?

 

My guess is magnesium from the aluminum alloy. :S

[YT2095]

no, alu foil is actually surprisingly Pure, to at least 2 decimal places back! yeah I know, I was quite astonished to find this out too

 

I`m not sure about the CuSO4 + KI rxn???

 

the easiest way normally is displace it with another Halogen further up the group.

if I get time in the morning (and I remember) I`ll try it and let you know

[John Cuthber]

"no, alu foil is actually surprisingly Pure, to at least 2 decimal places back! yeah I know, I was quite astonished to find this out too :)"

Sure about that? Decimal places of what?

http://www.enotes.com/how-products-encyclopedia/aluminum-foil

http://www.key-to-metals.com/Article119.htm

Also, in my experience it often leaves stuff behind when you dissolve it in alkali.

It's possible that the blackening refered too in the first post is bits of other alloy elements trapped in a (mainly KI) matrix.

Anyway the

2Cu++ + 4I- --> 2 CuI +I2

reaction is a classic for measuring Cu++ in solution.

The problem is that you lose half the I as CuI. Peroxide and acid seems to be the method of choice for the amateur scientist but there are lots of possibilities.

[dubois928]

Well it actually isn't aluminum foil, its a strip I cut off of a washed soda can. I used the un-printed side, though.

[John Cuthber]

The insides of drinks tins are varnished. Did you clean that off?

[dubois928]

I don't know. It doesn't look varnished to me. But I only cleaned it out with water. Maybe I'll try it on something else and see if it does the same thing.

 

Ken

[Melvin]

I would take a piece of Al can and a piece of Al foil. Add equal amounts of iodine tincture to each, then light. Compare the two when finished:-)

[John Cuthber]

Many soft drinks are acid enough to corrode a clean aluminium surface.

[Mr Skeptic]

Many soft drinks are acid enough to corrode a clean aluminium surface.

 

Is that scary, or what?

[Melvin]

Is that scary, or what?

 

That is kinda scary!

 

But, you have to remember that your very own stomach contains HCl, which is much stronger than the H2CO3 in soft drinks.

 

I assume that aluminum corroded by soft drinks is aluminum carbonate?

[YT2095]

there`s also Citric and Phosphoric acid in quite a few of these drinks, the later is a very strong acid, not as strong as sulphuric but stronger than Nitric!

and Thankfully Non-Toxic

[encipher]

there`s also Citric and Phosphoric acid in quite a few of these drinks, the later is a very strong acid, not as strong as sulphuric but stronger than Nitric!

and Thankfully Non-Toxic

 

How is Phosphoric acid stronger than nitric acid? Phosphoric acid is clearly classified as a weak acid, and nitric as strong.

[TiffanyAyala]

You have to know it from one service. https://www.nterlearning.org/forum/-/message_boards/message/3548792 here I saw a link to it. Try to seek there. I hope it'll help you!

 

Edited January 19, 2018 by TiffanyAyala