Molecular iodine in ethanol solution

[dddd]

Hello everyone,
Does iodine specie change after diluting in ethanol 99%? I’m talking about I-, KI or other kinds of of iodine species. Or it stays in I2 form?
I’m looking to make 1% I2 molecular iodine ethanol solution from iodine crystals.
Would the ratio be 10 g per 1 liter?

Thank you all for all inputs.

David

 

[symbolipoint]

How do you mean, "change"? Best I can understand, when dissolved in ethanol, the molecular iodine is as I₂.

But aside from that, you are not handling the concentration calculation properly.
That part seems ok. 10% of 1000 ml. is 100. 10% of 100 is 10. So, okay 10 grams solid iodine to dissolve in 1000 ml. ethanol.
.

 

[dddd]

Thank you,
I wasn’t sure since I2 molecular iodine is very reactive and does change as a specie, depending on the solution.
For example…. When you orally ingest I2 in aqueous solution, it changes in your body from Iodine I2 to Iodide I-.
If I understand this correctly.

I also wonder when you dilute the ethanol solution in water, does it then change from I2 to some form of iodide or iodate.

 

[symbolipoint]

I also wonder when you dilute the ethanol solution in water, does it then change from I2 to some form of iodide or iodate.

I do not believe so; but other members may have more refined knowledge.

 

[symbolipoint]

Some of that more refined knowledge I mention from other members could be, does iodine when dissolved (either in an alcohol or in water ) go through something like this?
2 I₂ <---> I₃⁺ + I^-

 

[Borek]

2 I₂ <---> I₃⁺ + I^-

I don't remember hearing about stable I₃⁺, I₃^-, on the other hand, is quite common and used to increase iodine solubility in water in the presence of iodides:

I₂ + I^- ↔ I₃^-

This is an equilibrium reaction, so in a way I₂ is "still there" and the solution is still highly reactive, just like I₂.

 

[dddd]

Yes, I believe you describe the Lugols solution.
That’s 5% I2, 10% KI as potassium iodide.

I wonder(in this case) what happens after you add the 99% ethanol I2 solution back to water, let’s say 10 drops.

Does it change its chemical structure? Or is it just molecular iodine I2 in water.

I could not find any information online about this.

 

[Borek]

Yes, I believe you describe the Lugols solution.
That’s 5% I2, 10% KI as potassium iodide.

Yes, but not only, iodine in KI is used as a titrant in iodometry and as a reagent whenever you need more iodine than the typical water solution can contain.

Or is it just molecular iodine I2 in water.

More or less.

This is never exactly trivial, solute is always solvated (surrounded by the solvent molecules that are weakly bound by Van der Waals forces). This is not considered to be a change in the structure nor described as a chemical reaction, but the boundary is not sharp.

 

[dddd]

Yes, so much we don’t know.
Thank you.

 

[snorkack]

I₂ in water does have a potential route to dissociate. First step:
I₂+H₂O↔HIO+H⁺+I^-
rapidly followed by
3HIO→HIO₃+2HI
with the net total
3I₂+3H₂O↔6H⁺+5I^-+IO₃^-
However, this is an equilibrium reaction. I understand that in neutral or mildly acidic conditions, the equilibrium is on the side of I₂, with little HIO or IO₃^- present in comparison. It is addition of base that shifts the reaction towards iodate.
Also when you have ethanol, you have the potential for reactions like:

1. CH₃CH₂OH+2I₂+H₂O=CH₃COOH+4HI
2. CH₃COOH+3I₂=CI₃COOH+3HI
3. CI₃COOH=CI₃H+CO₂

But this haloform reaction seems to also need base to go ahead. Iodine tincture is regarded as stable. At what pH does haloform reaction start, at least as unwanted side reaction? (You would probably use more base if you want the haloform reaction to go to completion. Which you can.)

 

[dddd]

Thank you!

That’s interesting!
When you say more base, you mean dissolve the iodine crystals in more ethanol?
Or iodine/ethanol drops in more water?

Also would my calculation be accurate to add 10 grams of I2 to 1 liter of ethanol to make 1% solution?

Last thing…
So do you think that I2 ethanolic solution changes when added to water or not?

Sorry for my lack of understanding the professional language.
I’m a total amateur in this department.

 

[snorkack]

Thank you!

That’s interesting!
When you say more base, you mean dissolve the iodine crystals in more ethanol?
Or iodine/ethanol drops in more water?

No. Something like NaOH. Or even a weaker base, like Na₂CO₃.

Also would my calculation be accurate to add 10 grams of I2 to 1 liter of ethanol to make 1% solution?

No. Because % would refer either to volume % (not straightforward, volume is not conserved on addition), or mass % (mass, unlike volume, is conserved).
The density of 100% ethanol at 20 C is 789 g/l, not 990 g/l. To get 1% iodine solution, you would need to add 1 g of iodine to 99 g solvent. Thus 7,97 g iodine to 789 g (1 l) ethanol.

Last thing…
So do you think that I2 ethanolic solution changes when added to water or not?

Not seriously.
I tried to track down just how much of iodine is in the form of acids in pure aqueous solution.
The total solubility at 20 C is quoted in the range of 0,25 to 0,3 g iodine per 1000 g of water. All sources agree that it is overwhelmingly molecular I₂ in the absence of bases; one source that offered numbers gave less than 0,01 g/l of iodine in the acid form (under 4% of the small amount of total iodine).
In pure ethanol, the solubility is in the region of 270 g I₂ per 1000 g solvent, all of it as I₂. Adding water would still leave most of iodine as I₂.
What would change things if you add a iodide or especially, if you add a base.

 

[dddd]

Amazing and detailed answer!

That’s my goal, to create a solution with mostly iodine (I 2) without adding any iodides, potassium, sodium etc…

I knew the solubility of I2 un water was insufficient, but wasn’t sure about reaction of ethanolic I2 with water later on.Thank you so much.
I really appreciate your input.

 

[symbolipoint]

dddd,

Use the correct notation. None of that I2, or I 2. Make use of the available subscripting from the tool bar or using the tags. Molecular Iodine, the diatomic elemental iodine, capital "I" and a subscripted "2" at the right.
I₂, iodine
"I" left square brack sub right square brack "2" left square brack forwardslash sub right square brack
(the quotation marks to not be included)

 

[dddd]

Sure thing .Understand.
Sorry for the use of incorrect notion.