Sciencemadness Discussion Board

Recrystallizing Zinc Chloride

CaptainPike - 26-10-2014 at 09:44

I got a great deal on some zinc chloride from overseas. I waited quite a while for it and I was excited when it finally came. A mysterious brown box, somewhat dogeared finally showed up – decorated with markings and cool stamps which may have been Art or Food, I'm not sure which.

All at once it came to me, the moment I touched the bag, "damn, I should've said anhydroussi zinc chloride". A couple of hours in the oven at 525°F should do the trick. The blackened zinc chloride was pretty crispy, I'll say that but deliquescent…ah, well, probably not quite that dry. Is there a zinc chloride monohydrate? I know there are a handful of hydrated states and I am sure I moved mine up the scale a couple of notches.

I read that it can be recrystallized in dioxane. Could dry acetone work too? Can I even purify this stuff that definitely attained a grayish coating over it, when it underwent its kitchen pyrolysis? It's definitely drier. Would washing with acetone, boiling even, remove any of this water of hydration? I'm asking now before I proceed any further. I wish I had asked a while ago.

I want anhydrous zinc chloride to perform some of the experiments in the Vogel book we adhere to so. In that book it refers to the anhydrous zinc chloride as "sticks"

I Like Dots - 31-10-2014 at 15:30

If I remember, once hydrated you can not obtain the anhydrous compound by heating, or any other means.. Take aluminum chloride for example:

The anhydrous phase cannot be regained on heating as HCl is lost leaving aluminium hydroxide or alumina (aluminium oxide):

Al(H2O)6Cl3 → Al(OH)3 + 3 HCl + 3 H2O

Yes, same principal with zinc chloride, once it is dehydrated it changes structure.
From wikipedia.

When hydrated zinc chloride is heated, one obtains a residue of Zn(OH)Cl e.g.[24]

ZnCl2•2H2O → ZnCl(OH) + HCl + H2O

As you probably know, the hydrated forms are not useful as lewis acids. Sorry bad luck.

[Edited on 31-10-2014 by I Like Dots]

Metacelsus - 31-10-2014 at 16:36

I thought that if you had excess concentrated hydrochloric acid you could go to anhydrous.

CaptainPike - 1-11-2014 at 09:34

Thank you, Dots for your educative response. I have little doubt that the pathway you have outlined, possibly along with others, has occurred, of course not completely, but sufficient to contaminate the product. I'm actually fortunate that my product was blackened by the attempted pyrolysis. Otherwise, I probably would've concluded success, since the results were quite crunchy. Somehow, the graying or darkening hints at even more exotic destruction… would this ZnCl(OH) be a dark color?

Hark, a challenge!

How do you say, pronounce, this offensive ZnCl(OH)? Zinc chloride hydroxide, or maybe zinc chlorine hydrate? Education is expensive, after all. And this seems to be the "autumn of product loss", as you may read another one of my posts outlining a goof-up in Halo-forming.

Accepting the challenge, there must be a way to separate through liquid extraction this decomposition product, ZnCl(OH), from the (supposed) ZnCl2*nH2O, right? I recognize the economic futility in trying to recover my zinc chloride. But again, it presents an exercise in analysis and recovery. No learning process is a waste.

And, CC, did you mean concentrated HCl before/instead of the baking in the kitchen stove? Or did you mean as part of some kind of recovery process? I am reluctant to put water (although I love and admire it so) with the stuff, since it's exactly what I was trying to remove :-(

[Edited on 1-11-2014 by CaptainPike]

Metacelsus - 1-11-2014 at 11:13

I meant having a solution of zinc chloride in concentrated HCl, and evaporating to dryness. I'm not entirely sure about this working, however.

It's zinc chloride hydroxide, by the way.

blogfast25 - 2-11-2014 at 10:04

Quote: Originally posted by Cheddite Cheese  
I meant having a solution of zinc chloride in concentrated HCl, and evaporating to dryness. I'm not entirely sure about this working, however.

That would give a hydrate, not anhydrous ZnCl2. The latter can be obtained from the hydrate by heating it in a stream of dry HCl.

[Edited on 2-11-2014 by blogfast25]