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Author: Subject: Elemental iodine from KI and bisulfate - results
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[*] posted on 2-12-2020 at 20:42
Elemental iodine from KI and bisulfate - results


Given sulfuric acid can be used to make iodine from iodide I figured I'd give it a go with sodium bisulfate.

I don't have a yield yet as I'm not sure what's the best way to remove it from the flask (scrape it?) but it looks promising given how little I used.

Input was 15g of KI I bought of ebay (A$13 for 100g) and 25g of NaHSO4.





I had the 100ml flask heated on a hotplate but all the iodine ended up solidifying in the three way joint. After cracking the 100ml flask when a clamp slipped from my hand I decided to put the whole assembly in the oven with the receiving flask in a bowl of water. It only took about 10m at 150C for everything to end up in the receiving flask.

Some notes and observations:

I didn't mix it very well as I could see some powdery KI on the bottom of the flask when I finished so I might get better yield next time doing a proper mixing job.

I may next time just try the whole thing in the oven from the start instead of messing around with a hot plate. The hot plate was at about 230C when it finished so it's achievable in a oven.

There was a strong smell at the start. It was almost sulfurous but something was off about it.

The stopper on the second neck was on loosely to release pressure.

Edit:

I ended up just washing it out. Got 5.5g of slightly damp iodine. Maximum yield should have been 11.5g, giving me 44%.

I left quite a bit on the filter paper though which I've stored in a container for later recovery. I'm also hopeful to get better yield from better mixing. I'll post results when I do.

[Edited on 3-12-2020 by Download]
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[*] posted on 2-12-2020 at 23:55


I wonder if it is possible to pass steam through your NaHSO4/KI mix. Steam condensation should be more straightforward, creating less mess with sublimation inside the condenser. Steam distillation is a standard method to purify iodine, by the way, see Brauer.
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[*] posted on 3-12-2020 at 14:12


The chemical equation is :

4 NaHSO4 + 4 KI --> Na2SO3 + K2SO3 + Na2SO4 + K2SO4 + 2 I2 + 2 H2O

It means that 166 g KI reacts with 120 g NaHSO4

As you have used a large excess off NaHSO4, you may have produced the reaction :

2 NaHSO4 + Na2SO3 --> 2Na2SO4 + SO2 + H2O

and H2O, SO2 and I2 do react to produce :

2 H2O + SO2 + I2 --> H2SO4 + 2 HI

This reaction may explain why your yield was so low. Part of the iodine has been transformed into hydroiodic acid HI !
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