Sodium Iodide

[YT2095]

yesterday morning I made a saturated soln of Sodium Iodide by dissolving NaOH and Iodine crystals in hot deionised water, the exact amount was "titrated" using solid media to leave a clear soln of NaI.

upon cooling overnight Crystals have started to form.

 

now in my books NaI is listed as being a Cubic crystal, and yet these I have here are quite clearly monoclinic!

 

any Idea what`s goin on?

[woelen]

When you dissolve iodine in a solution of NaOH you do not only get sodium iodide! You also get sodium iodate:

 

[ce]6OH^{-} + 3I2 -> IO3^{-} + 5I^{-} + 3H2O[/ce]

 

Sodium iodate apparently is somewhat less soluble than sodium iodide (although it still is quite soluble). By dissolving iodine in a solution of an hydroxide salt it is hard to obtain pure iodide. The iodate, formed in the reaction, is a very disturbing impurity.

 

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If you really want sodium iodide in a fairly pure state, then you could do as follows:

 

Dissolve some iodine in a solution of sodium hydroxide. Use a slight excess of iodine, such that the solution is light brown. This solution contains iodide-ions, iodate-ions, sodium ions and a very small amount of free iodine (loosely bound to iodide-ions, but that is no problem).

 

Next, evaporate the solution to dryness and then put the dry stuff in a crucible (porcelain, not metal, because that gives other impurities). Next, heat strongly. The tiny amount of iodine, remaining in the solid evaporates, the solid will become white. Also, the iodate decomposes, giving off oxygen, leaving iodide behind. Unfortunately, there most likely also will be a side reaction, where the sodium iodate (NaIO3) decomposes, not to give sodium iodide and oxygen, but iodine vapor, oxygen and Na2O. But I expect this impurity to be of very low concentration.

[encipher]

Is it possible to make sodium iodate this way? Do you know of a good pocedure for making sodium iodate and purify it? (sorry if my question is a bit off topic)

[YT2095]

DAMN!

[woelen]

YT, no need to worry about lots of lost chemicals. Add a VERY small amount of additional iodine, until your solution become light brown. Heat it a little to have your crystals redissolved again. Then proceed as described in the post above.

 

@encipher: Making sodium iodate in the pure state is not that easy. It dissolves quite well in water and is hard to separate from the sodium iodide. You could, however, make potassium iodate fairly easily. Solubility of potassium iodate is much less. So, if you start from concentrated KOH and add iodine, you could precipitate KIO3 quite easily.

This route to iodate from iodine, however, is not a very efficient route, because only 1/6-th part of the iodine goes into the iodate, the rest goes to iodide.

 

Making iodates usually is done as follows:

 

Take some iodine, mix this with solid KClO3. Add some concentrated nitric acid and start the reaction with careful slight heating. When this is done, then the reaction sets off and a lot of chlorine gas is released and a white solid is formed. This white solid is a mix of KIO3 and HIO3, forming an impure double salt KIO3.HIO3, with remains of nitric acid and chloride/chlorate trapped inside. This mix then in turn is separated from the liquid and dissolved in a small quantity of hot water and carefully KOH is added, until the liquid is slightly alkaline. Then the liquid is allowed to cool down and crystals of KIO3 settle at the bottom. These are fairly pure. Removal of the last traces of chlorate/chloride/nitrate can be done by redissolving this solid in an as small as possible amount of hot distilled water and letting crystallize again and slowly cooling down to almost 0 degrees C.

[YT2095]

I didn`t realise that these were also Shock sensitive though!

 

yes, I think I`ll add the excess iodine NOW, I`m not too pleased having material like around, esp as I wanted to store it after for later use.

and not only that but the iodATE will Kill plants, and not provide the Iodine trace that I wished for.

[woelen]

YT, iodates are perfectly safe on storage and they are not shock sensitive. I have 250 grams of KIO3 lying around and this stuff is perfectly stable. It is an oxidizer, but its energetic properties are only a pale shadow of the energetic properties of KBrO3 and KClO3. Mixing KIO3 with reductors hardly gives an energetic mix. It just smoulders and smokes, but no violent reactions as with KBrO3 or KClO3.

KIO3, however, can be used for very interesting experiments. It allows you to make KICl3, which is an energetic compound and shows lovely reactions, when mixed with finely powdered magnesium, such as giving purple clouds of iodine vapor on ignition (it ignites when mixed and a drop of water is added).

 

http://woelen.scheikunde.net/science/chem/exps/KIO3+HCl/index.html

 

Iodate probably does kill your plants. But, how much NaI you would like to add to your plants? You realize that iodine is a trace-element? It only is required in microgram quantities and having too much is quite harmful in the long run, both for the plants, but also for you, if you consume the plants.

[jdurg]

You could always do what I did and that's make NaI directly from its elements. It's not as easy to do as one would think as it takes some effort to get the reaction going (and the iodine fumes get pretty nasty), but it will result in fairly pure NaI. Afterward, there will be some NaOH left over in there, but you can always take a very dilute HCl solution to neutralize that, or even some vinegar. In the concentrations that are used, the impurities won't be too bad. The bulk of your product will be NaI.

[YT2095]

well, I`ve been out the majority of the day working, but I left the flask with my "product(s)" on my desk after adding excess iodine and some extra de-ionised water (figured it would be better than heating to re-dissolve the iodATE).

anyway, I came back and what was Once a nice reddy brown was now clear again!

there is some iodide missing also.

I`ve done this again since, and end up with a red/brown, that after much stirring goes orange, then yellow and then clear once again.

and I lose some more Ioadate.

I seriously DON`T want to heat this mixture just yet untill all the monoclinic crystals dissolve.

 

and yes Sodium Iodate IS shock sensitive according to the MSDS pages I read.

now I don`t mind energetic materials one little bit, but if it`s something I`m unfamiliar with, I simply won`t mess!

 

call me a Chicken if you like, but I hate Unpredictability with such things. I dunno,,, maybe I`m just getting old?

[encipher]

I used sodium/potassium iodate quite frequently with landolt reactions (iodine clock reactions). I would sometimes raise the temperature of the solution to a boil before carrying out the experiment. MY experience with iodate tells me its pretty stable, and I'm pretty damn sure it's not that 'shock sensitive' or else i wouldnt be alive

[YT2095]

this would seem to lend itself towards the Negative of your statement: http://physchem.ox.ac.uk/MSDS/SO/sodium_iodate.html

 

what am I to beleive?

 

I think it prudent to err on the side of Caution.

[encipher]

Yeah, i agree.. better safe than sorry. Buuut.. only one way to REALLY find out =D Just kidding. I see what MSDS says, I'm just telling you what I've had experience with. Mabe it requires more heat than what I gave it. Oh yeah, and Potassium iodate is commonly used (alongside KI) as an anti-radation pill. I doubt if it were really that shock sensitve they would be selling it as pills...

[YT2095]

Oh yeah' date=' and Potassium iodate is commonly used (alongside KI) as an anti-radation pill. I doubt if it were really that shock sensitve they would be selling it as pills...[/quote']

 

Sorry and everything, but that has to be amongst the top 5 in Dumb comparisons used to make a point, Nitro-Glycerine is used in Angina heart tablets too, Patients Don`t explode either, so is NG also not Shock sensitive?

 

I think I`ll practice my current proceedure and adhere to Woelens advice for the rest.

 

Thnx anyway

[encipher]

I don't want to agrue or anything, but you cant compare nitroglycerin medications with KIO3 medications either. There is less than 1% of nitro that can be in your body at one time (meaning probably less in the actual medicine) as opposed to a bottle containing 200 tablets of solid KIO3. Mabe it wasn't the best comparison in the world, but it certianly isnt 'dumb'.

[YT2095]

although K and Na share many similarities, you`de have to be crazy to consider them the same.

and so I have no idea about KIO3`s stability and thus i refuse to comment upon it.

the MSDS was based upon Sodium Iodate, and I cannot reasonably refute the information that was given or contained therein.

 

based upon that, my choice would be that of the SAFEST option of all presented.

[woelen]

YT, again, KIO3 is not shock sensitive in any practical sense. That MSDS is exaggerating strongly. I fully agree with encipher.

 

I have done a lot of experiments with KIO3. I heat the stuff, mix it with all kinds of acids, and I molest the material in many other nasty ways , but it simply is not energetic enough to be of a real danger in those situations.

 

If you dare to mix KClO3 with conc. HCl for etching PCB's, or if you dare to heat a solution of KClO3 in water, then you certainly can heat a solution of KIO3/NaIO3 in water. Iodate is to chlorate what a scootmobile is to a Ducati 999R.

[YT2095]

ok we`re talking SODIUM iodate here though, NOT potassium for a start.

second Why might they "Exagerate"?

 

I think Woelen understands my situation here quite well and perhaps understand WHY I may be so cautious with such things so close to home.

I MUST run on a Zero or less-than risk factor in everything.

[woelen]

Sodium- and potassium iodate are VERY similar with respect to energetic behavior. Just think of sodium chlorate and potassium chlorate, or sodium nitrate and potassium nitrate. Of course, the potassium salts are more suitable for pyro-work, but that is not because they are more energetic (in fact, they are even less, they deliver less KJ/mol of energy), but because they are not hygroscopic.

 

And YT, I understand why you want to be very cautious. You have a lot to loose, just like I have. So, indeed, if you don't know the properties of a certain compound, then you'd better be very careful. But in the case of both KIO3 and NaIO3, trust me, they can be used for many experiments without the need to fear accidental explosions and so on.

[jdurg]

Remember one important thing about MSDS sheets; The labels they use to classify the compounds are based upon certain criteria set forth by OSHA, I believe. (Or whatever company is in charge of creating MSDS Sheets). I mean, if you look at the MSDS sheet for water it will make it sound like the most vicious of chemicals.

 

Ammonium Nitrate is also considered a shock sensitive compound, however I'm pretty certain you wouldn't be timid about using/storing NH4NO3 would you?

 

With the MSDS sheets, even if it requires a high level detonator to get it going, it will be classified as heat/shock sensitive.

[woelen]

This is why I hate MSDS sheets. To my opinion they even can introduce additional danger, because they do not discrimiate between "some danger" and "a lot of danger".

 

Compare the MSDS sheets of e.g. NaCl and NaOH from the same manufacturer.

 

http://avogadro.chem.iastate.edu/MSDS/NaCl.html

http://avogadro.chem.iastate.edu/MSDS/NaOH.html

 

In both cases the MSDS states that you should use safety glasses (with side protection), gloves, protective clothing, and a NIOSH/MSHA approved air purifying dust or mist respirator. If you read such a thing about NaCl, then you can only laugh about that. Now, the same things are written for NaOH. For that chemical glasses certainly are a very good thing, and gloves also are a must. I also noticed the very acrid and biting smell of a concentrated hot solution of NaOH, so if you work with large quantities then some form of ventilation also is highly recommended.

In MSDS's there only are very dangerous chemicals, extremely dangerous chemicals and ultra dangerous chemicals . That is a pity. People do not learn to discriminitate between things which are somewhat dangerous, and things which are REALLY dangerous. This can lead to accidents, because uninformed people tend to get used to dangers mentioned in documents and because there hardly is any discriminating effect, they are working easily and comfortable with fairly innocuous chemicals and the really dangerous ones.

 

Here, YT has found another bad example of MSDS's. KClO3 and KIO3 both are called impact sensitive. We all know that KClO3/reductor mixes sometimes can go off, even when carefully mixed on a sheet of paper with a soft flexible stick. If you want a KIO3/reductor mix (same reductor) want to set off, then you might succeed if you put it on a steel plate, heat it to 400 degrees and hit it with a heavy sledge hammer. Even then, I severely doubt, whether the mix will set off. Probably you even need a very powerful primary high explosive to set off a mix of KIO3 and a reductor. Yet, the MSDS's for both warn for the same risks. YT now is somewhat overcautious with iodates, because he knows the dangers of chlorates. But the other way around is much more dangerous. Someone, used to working safely and comfortably with iodates, but unfamiliar with chlorates, may think that chlorates have the same risks (same warnings in MSDS) and at a bad day thay may have a serious accident.

Also, if you study the MSDS of bromates, then things are even worse. These are even more sensitive than chlorates (I noticed personally), but the MSDS does not state that at all. From MSDS's you would conclude that bromate, iodate and chlorate all are oxidizers and very dangerous, but there is no difference at the warning level.

[YT2095]

I think what seemed to make my suspicion even greater was that I remember you saying about bromates being even greater sensitivity than chlorates, and so going down the list of halogens with Iodine coming after Bromine it seemed logical that this material was indeed very dangerous.

I`m curious however, of the Halogens which one would be the most sensitive?

idealy in what order of sensitivity would they occur?

 

anyway, back to the iodide(ate) it`s all dissolved now with excess iodine (looks like tea at the moment). I did notice though, while adding crystal at a time, the color would go from tea(ish) brown to yellow then to clear again.

it did this several times, now it`s not changed, so I`ll need to evaporate to dryness now, and hopefully not make this place smell TOO Much like a hospital

[woelen]

Sensitivity of the oxo-halogenates is as follows, starting with the most sensitive, ending with the least sensitive (from a pyro point of view):

 

bromate

chlorate

periodate

perbromate

perchlorate

iodate

 

So, iodate is the least powerful of all. Strangely, when we look at the perhalogenates alone, then indeed the periodate by far is the most sensitive. I have periodates and perchlorates, and the periodates are much more reactive than perchlorates, and also much more reactive than perbromates. Written somewhat different:

 

bromate > chlorate >> periodate > perbromate > perchlorate > iodate

 

Here, bromate and chlorate both are much more reactive than all the others.

 

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In aqueous solution the order of reactivity is somewhat different:

 

bromate/periodate

chlorate/iodate

perbromate

perchlorate

 

In aqueous solution, bromate and periodate are very reactive. Chlorate and iodate are about equally reactive and perbromate and perchlorate are almost inert in aqueous solution.

 

So, writing it somewhat different:

 

bromate ≈ periodate > chlorate ≈ iodate >> perbromate > perchlorate

 

Perbromate and perchlorate are much less reactive than the others in aqueous solution. I once boiled a strongly acidified solution of NaClO4 with sodium iodide, and the perchlorate was not capable of oxidizing it, not even near boiling conditions!

[YT2095]

Fascinating!

 

what is the reasoning behind this though, How does it work in such ways?

it certainly doesnt follow the halogen table in order, it seems to Jump-over and then come-back-to.

 

I can`t see a Pattern, and that frustrates me.

[woelen]

Understanding these patters indeed is very difficult. There is some pattern, but then you need to broaden the view to other parts of the periodic table. When you look at the highest oxidation state compounds of chlorine, bromine and iodine, and you compare that to the corresponding compounds of sulphur, selenium and tellurium, then you see a similar pattern. Sulphate is the most inert of these, the selenate is hardest to make, but once you have this compound, it is less reactive than selenite. Tellurate is easier to make than selenate. The resemblance is not 100%, but there definitely is a pattern. Again, a similar pattern exists for phosphate, arsenate and antimonate, but here the pattern is much less pronounced.

[bob000555]

Wiki says its shcok sensitive.

http://en.wikipedia.org/wiki/Sodium_iodate