Sciencemadness Discussion Board

Synthesis of Zinc Chloride (Hydrate)

sdonell - 30-11-2011 at 16:22

Good Evening.

I seek the expertise of the users here on a relatively simple matter regarding the synthesis of zinc chloride.

I have reacted mossy zinc chloride with excess 12 M aqueous HCL. The mixture was heated for several hours. Initially, the reaction was vigorous, and over the course of a few hours has now become slower. The reaction has "stabilized" now, and by this, I mean only that there is a continuous, steady "bubbling", which seems to indicate to me that not all of my zinc has reacted yet.

Additionally, there are still several large chunks of the mossy zinc metal sitting in my reaction vessel, which I again perceive to be yet-unreacted zinc. However, there is a great deal of a dark, almost black colored powered that has formed in the reaction vessel.

I removed the vessel from the heat, and filtered the mixture. The filtered solution is milky white (zinc chloride dissolved in HCL?), and the filtered powder is dark Gray.

MY QUESTION: Where is my zinc Chloride? Is it the dark gray powered that I filtered out of the solution? And what about the white-milky-filtered solution? I know that anhydrous Zinc Chloride is a white crystalline substance, but since I am using HCL acid as opposed to HCL gas, I don't expect to end up with the anhydrous form. I realize that I never allowed everything to react fully, but what I am looking for is to create a zinc chloride reagent for use in the synthesis of Isopropyl Chloride. I have a full scale lab in reagards to glassware. I have a limited quantity of assorted reagents.Any help here is greatly appreciated.

[Edited on 1-12-2011 by sdonell]

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[Edited on 1-12-2011 by sdonell]

[Edited on 1-12-2011 by sdonell]

bbartlog - 30-11-2011 at 17:19

Knowing something about the quantities you used would be helpful. Anyway: the dark gray powder is not zinc chloride. I would assume that it is an impurity. Depending on your source of HCl, I suppose it could be that some other metal was dissolved in the HCl and was then reduced and precipitated.
Zinc chloride is really very soluble in water, but I suppose that excess HCl could reduce that solubility drastically enough that your milky white suspension is fine particles of the stuff.

sdonell - 30-11-2011 at 17:28

Quote: Originally posted by bbartlog  
Knowing something about the quantities you used would be helpful. Anyway: the dark gray powder is not zinc chloride. I would assume that it is an impurity. Depending on your source of HCl, I suppose it could be that some other metal was dissolved in the HCl and was then reduced and precipitated.
Zinc chloride is really very soluble in water, but I suppose that excess HCl could reduce that solubility drastically enough that your milky white suspension is fine particles of the stuff.


Hey Thanks for the response. Initially, I started out with 107 grams of mossy zinc and a stoichiometric equivalent of HCL, but I later ended up adding addition HCL.

Honestly, If I had to guess, I would guess that the gray powder is simply disintigrated zinc metal. As I look over at my filter flask now as we speak, it seems that a white solid powder has fallen out of the milky-white filtered solution, and is now sitting on the bottom of the flask.

If this is my zinc chloride, I feel I am good shape.

ONE LAST QUESTION: Tell me what you think about my plan for synthesizing Isopropyl Chloride:I put 10 or so ml of isopropanol in a 25ml round bottom flask. I add excess 12 M HCL + the zinc chloride (white) powder. I will use a water-jacketed condensor to reflux the mixture for 2+ hours. Think it will work?I realize that Isopropyl Chloride is a gas at as low as 35°C, but I'm hoping that if I'm refluxing the reaction sufficiently, it won't all escape when I heat everything.What do you think?

Dr.Bob - 1-12-2011 at 10:59

Quote:
Initially, I started out with 107 grams of mossy zinc and a stoichiometric equivalent of HCL, but I later ended up adding addition HCL.

Honestly, If I had to guess, I would guess that the gray powder is simply disintigrated zinc metal. [/rquote]

You need a large excess of HCl in the reaction to drive it to completion in a reasonable time. The grey material is excess zinc, as if you only have one equivalent of HCl, the reaction will slow down as the reaction goes to completion, as the concentration of acid is approaching zero since you are using it up. Since you will be adding HCl to the next step anyway, why not use 2 or 3 equivalents of HCl, which will dissolve the zinc much faster.

[/rquote]ONE LAST QUESTION: Tell me what you think about my plan for synthesizing Isopropyl Chloride:I put 10 or so ml of isopropanol in a 25ml round bottom flask. I add excess 12 M HCL + the zinc chloride (white) powder. I will use a water-jacketed condensor to reflux the mixture for 2+ hours. Think it will work?I realize that Isopropyl Chloride is a gas at as low as 35°C, but I'm hoping that if I'm refluxing the reaction sufficiently, it won't all escape when I heat everything.What do you think?[/rquote]

If you are refluxing it sufficiently, that implies that it is boiling at the BP of isopropanol, which would cause any and all product to evaporate. If you put a distillation head on top of the reflux condenser and then a very cold condenser and ice trap pointing down towards a chilled flask, you might be able to condense the isopropyl chloride that way. You will need to be careful to keep it sealed and dry, as otherwise you will collect condensation, which will improve your yield dramatically. :-)

Bob

blogfast25 - 1-12-2011 at 13:53

Possible causes of any precipitation when preparing ZnCl2 hydrate from Zn and HCl:

1. solution has become saturated: ZnCl2 or a hydroxychloride starts crystallising.
2. hydrolysis of ZnCl2 to less soluble hydroxychlorides, due to low remaining acid concentration of solution.

Obtaining crystals of the hydrate may not be so easy: if the acid reserve in the solution is low, hydrolysis will be promoted. Always uses a strong excess of acid. When crystallising, avoid heat towards the end.

sdonell - 1-12-2011 at 16:30

Well, I ended up filtering out a small (few grams) quantity of very fine, white colored crystals. Again, these were originally formed (whatever they may actually be) during the reaction of my zinc in my HCL. When I passed the whole reaction mixture through my filter, the solution that filtered through was the milky white liquid. Eventually, the fine white particles then fell out of solution (they appeared to have been suspended) and settled on the bottom of my filter flask.

I may be misguided here, but I'm thinking perhaps I will try and prepare some 1-Chlorobutane instead of the isopropyl chloride. I have n-butyl alcohol on had, 1-Chlorobutane has a higher boiling point than does the isopropyl chloride. Though, now that I think more about this, the boiling point factor may really have really no actual benefit to me....

As far as the glassware setup goes, I was merely going to do: round bottom flask + slightly-oversized Liebig condensor. As this is a home lab, and I have no water faucet nearby, I'll be using a siphon system to move the water through the condenser. This is advantageous, because I can actually put colder-than-tap water through my condenser. It does require me to physically prime the siphon about every 5 minutes, but I've used the same setup multiple times before when distilling stuff, and it works like a charm.

The reason I say this is because it gives you an idea regarding the extent to which I am capable of condensing my product as it tries to escape. I don't have any "Cold Finger" apparatus, etc...

[Edited on 2-12-2011 by sdonell]

[Edited on 2-12-2011 by sdonell]

entropy51 - 1-12-2011 at 17:24

Quote: Originally posted by sdonell  
As this is a home lab, and I have no water faucet nearby, I'll be using a siphon system to move the water through the condenser. This is advantageous, because I can actually put colder-than-tap water through my condenser. It does require me to physically prime the siphon about every 5 minutes, but I've used the same setup multiple times before when distilling stuff, and it works like a charm.
Do a Google search using the words Sunterra, Fountain, and Pump and you will find nice little pumps for about $10 that you can use to pump water from a bucket of water into your condenser.

I believe that the zinc chloride used for alkyl chloride synthesis must be anhydrous. I don't think the hydrate will be very effective.

[Edited on 2-12-2011 by entropy51]

bbartlog - 1-12-2011 at 17:29

Ice water is good if you're going to condense isopropyl chloride.
As for the synthesis, though - unless I'm missing something, your system will have too much water in it for the reaction to proceed. The prep in Vogel (which is in the library on this site) uses a relatively large quantity of anhydrous ZnCl2 to compensate for the use of aqueous HCl. Other syntheses use gaseous HCl. I'm assuming you plan to use ZnCl2 hydrate with 31% aqueous HCl, or similar, and that is likely to be too much water.
One workaround that I used with limited success back when I did this synthesis was to mix the aqueous HCl and the isopropyl alcohol, then dry the resulting solution with a fairly large quantity of anhydrous MgSO4. The result is nowhere near anhydrous, but you can remove enough water from the system this way that results can be achieved even with ZnCl2 hydrate.

sdonell - 1-12-2011 at 17:47

Quote:

Do a Google search using the words Sunterra, Fountain, and Pump and you will find nice little pumps for about $10 that you can use to pump water from a bucket of water into your condenser.


Hey, thanks a ton for the tip there buddy. I knew I would really get a lot of value by beginning to get active on a forum of similar minded people. I'm definately going to check that out.:cool:
Quote: Originally posted by bbartlog  
Ice water is good if you're going to condense isopropyl chloride.
As for the synthesis, though - unless I'm missing something, your system will have too much water in it for the reaction to proceed. The prep in Vogel (which is in the library on this site) uses a relatively large quantity of anhydrous ZnCl2 to compensate for the use of aqueous HCl. Other syntheses use gaseous HCl. I'm assuming you plan to use ZnCl2 hydrate with 31% aqueous HCl, or similar, and that is likely to be too much water.


I feared it would come to this. I have a backup plan in my head for creating anhydrous ZnCl2, but it would not work out with the equipment that I have if it involved more than 1 atm of pressure or >1000°C temps. I can generate HCL gas from H2SO4 + NaCL, but it would be a poor use of my H2SO4, and I think my yields would suck.
Quote:
One workaround that I used with limited success back when I did this synthesis was to mix the aqueous HCl and the isopropyl alcohol, then dry the resulting solution with a fairly large quantity of anhydrous MgSO4. The result is nowhere near anhydrous, but you can remove enough water from the system this way that results can be achieved even with ZnCl2 hydrate.


I like work-arounds! This is the ART in chemistry.

However, maybe at this point, I will just redirect my efforts to trying to confirm that my white particles are actually hydrates of ZnCl2. I'm thinking a melting-point determination would be called for here.

And I might just leave it at that. It's a bummer I have to spend my time making relatively harmless precurssor reagents because chemical companies see everyone as drug makers. :)

[Edited on 2-12-2011 by sdonell]

Endimion17 - 1-12-2011 at 18:41

The black stuff always appears when technical grade zinc is dissolved in hydrochloric or sulphuric acid. It could be a mixture of finely divided lead together with arsenic. All impure zinc samples I've tested (Marsh) so far are positive for arsenic, and lead usually follows zinc around in nature.
I've never analyzed the black stuff itself, though.

entropy51 - 1-12-2011 at 21:14

Quote: Originally posted by sdonell  
And I might just leave it at that. It's a bummer I have to spend my time making relatively harmless precurssor reagents because chemical companies see everyone as drug makers.
I don't know why you think that. The rest of us buy chemicals without having our door broken by federal agents. There are companies that will sell you zinc chloride. For example www.elementalscientific.net. But I have learned a lot of chemistry by making the precursors that I needed. It's all chemistry, you know. If I thought making chemicals was a waste of time I would find another hobby.

bbartlog - 2-12-2011 at 09:01

Quote:
The black stuff always appears when technical grade zinc is dissolved in hydrochloric or sulphuric acid.


Given the quantity shown, though, I'd be inclined to agree with a previous poster that in this particular case it's mostly just unreacted zinc. I have also seen small amounts of a black residue / impurity when dissolving post-1982 US pennies: the zinc dissolves out (assuming you score the copper coating), leaving a thin copper shell. The inside of this shell has a small quantity of insoluble black material on it. However, it's not clear to me what this material would be. Cadmium chloride, lead chloride, tin chloride (all plausible impurities) - those are all white. Silver chloride? That's black, but it seems unlikely that they would leave enough silver in either the copper or the zinc for it to leave visible deposits like that. In the case of the coins I had thought that perhaps they used an organic flux in whatever copper coating process is used to make them, and that what I saw was minute quantities of carbon residue; but now you have me wondering. Maybe next time I dissolve zinc pennies I'll see if I can narrow it down.

Alastair - 17-12-2011 at 06:19

I have tried percipitating Zn(OH)2 from ZnCl2 and what i thought was FeCl2 or FeCl3 with aqueous NaOH. Its a white insoluble powder (although in one schoolbook was listed as green). Imo its a good way to see if your material is pure or electroplated/coated.

AJKOER - 10-1-2012 at 18:41

An old method for preparation of ZnCl2 (and KClO3, which for the most part, is precipitated out):

"Zinc Chloride and Potassium Chlorate.—An interesting method for the preparation of zinc chloride in connection with potassium chlorate has been described by K. J. Baver [1]. In carrying out this process chlorine gas is passed into zinc oxide suspended in cold water, whereby zinc chloride and zinc hypochlorite are first formed, the whole of the zinc going finally into solution. According to the following equation:

2 ZnO + 4 Cl = ZnCl2 + ZnCl202.

1. Chem. Ztg., 1805, XIX, 1453 to 1453; Journ. Soc. Chem. Ind., Jan. 31, 1806, p. 32.

The zinc hypochlorite is converted into zinc chloride by potassium chloride, potassium chlorate being formed in the reaction as follows:

3 ZnCl202 + 2 KCl = 3 ZnCl2 + 2 KCl03

The potassium chloride may be added to the zinc oxide in the beginning or after the solution of the zinc has been effected, the temperature being maintained at 90 to 95° C. In either case a solution of about 30° B. is obtained which on cooling yields fairly pure crystals of potassium chlorate. On concentrating the mother liquor to about 60° B. the greater part of the remaining potassium chlorate crystallizes out. The mother liquor, then containing only very little potassium chlorate, is treated with chlorhydric acid and evaporated to dryness to obtain zinc chloride. The apparatus required differs but little from that which is used in the manufacture of potassium chlorate by the lime process, the two processes being indeed identical in their reactions with the only difference that zinc oxide is substituted in one for calcium oxide in the other. The evaporation of the zinc chloride solution may be carried out in iron vessels, preferably in a vacuum, if traces of iron are not detrimental. The zinc process is claimed to give a better yield of potassium chlorate than when either lime or magnesia is employed, and of course the whole of the chlorine used is btained as a marketable product. The zinc chloride which is produced is very pure but may contain a little potassium chloride, which, however, is not detrimental for many purposes."

Source: "The metallurgy of zinc and cadmium", by Walter Renton Ingalls, pages 686 to 687.

http://books.google.com/books?id=RnhUAAAAYAAJ&pg=PA687&a...

Note, I don't believe the author's statement "The zinc hypochlorite is converted into zinc chloride by potassium chloride". In actuality, my opinion is that given the inherent instability of Zinc hypochlorite, the Zn(OCl)2 has disproportionated into ZnCl2 and some Zn(ClO3)2 in the presence of HOCl (in the Chlorine water). More precisely:

ZnO + H2O + 2 HClO --> Zn(ClO)2 + H2O

Then, in the case of Zinc hypochlorite, being highly unstable, there rapidly occurs a multi-stage disproportionation reaction forming the chlorate in the presence of HOCl in a slightly acidic environment (pH 5.5):

Zn(OCl)2 + 2 HClO = Zn(ClO2)2 + HCl

Zn(ClO2)2 + 2 HClO = Zn(ClO3)2 + HCl

The common industrial process for Chlorate production does not directly employ HClO, but instead passes Chlorine into solution (forming HClO) and lowing the pH (good for chlorate formation) by creating HCl:

Cl2 + H2O <---> HClO + HCl

The KCl then reacts as follows to remove the Zinc chlorate (a step you will still need):

2 KCl + Zn(ClO3)2 --> 2 KClO3 + ZnCl2

adding to the ZnCl2 formation.

[Edited on 11-1-2012 by AJKOER]

dchainy - 14-6-2012 at 06:52

Hey guys I' new here so I'm not going to make waves.
But I've been playing with ZnCl2 idea for the last few days and it seems to be doing something right.
I'm dropping Zinc from lantern batteries in to 100mL of Muriatic Acid. (small batches).
I've found that the white stuff is the Zinc Oxide.

The steps are the zinc goes into solution real fast in the beginning, but as the HCL gets used up it naturally slows down.
The the Oxide takes over for the HCL. Zinc Oxide continues to grow along with the ZnCl2.

Then I boil off most of the water. Oh I filter first. derp. I boil till there's a massive color shift.
The at that point what ya have is good old fashion "Tinner's fluid" a flux for soldering.
And by the way I testes that soldering 2 coffee cans together last night.
Stuff works like a charm.

Also if you want to know if you did it right pass some H2S into it and see what happens. You'll get ZnS.
And that's my next step to do later.

-----
If I'm out in left field I must of discovered something because it's working.
So go easy on the NOOB here. :)

blogfast25 - 14-6-2012 at 07:09

Quote: Originally posted by dchainy  

I've found that the white stuff is the Zinc Oxide.

The steps are the zinc goes into solution real fast in the beginning, but as the HCL gets used up it naturally slows down.
The the Oxide takes over for the HCL. Zinc Oxide continues to grow along with the ZnCl2.

Then I boil off most of the water. Oh I filter first. derp. I boil till there's a massive color shift.

The at that point what ya have is good old fashion "Tinner's fluid" a flux for soldering.

And by the way I testes that soldering 2 coffee cans together last night.

Also if you want to know if you did it right pass some H2S into it and see what happens. You'll get ZnS.


What ‘white stuff’?

“Zinc Oxide continues to grow along with the ZnCl2.” Huh?

“massive colour shift”. Huh?

At low pH H2S will not precipitate ZnS, it’s solubility product is too low. Oooopsie: too high of course!


[Edited on 14-6-2012 by blogfast25]

[Edited on 14-6-2012 by blogfast25]

dchainy - 14-6-2012 at 08:08

I'm assuming the cloudy white junk everyone is talking about is the ZnO.

Yes after the HCL is all used up there's still more bubbling and that's the raw zinc oxidizing.

Before boiling the solution is a clear/greenish tint.
But as I'm boiling the water off at about 50% I see a rapid shift to very dark green. Almost black.

Right or wrong it's doing something.

Oh and thanks for going easy on me, Dick.

blogfast25 - 14-6-2012 at 09:17

Quote: Originally posted by dchainy  
I'm assuming the cloudy white junk everyone is talking about is the ZnO.

Yes after the HCL is all used up there's still more bubbling and that's the raw zinc oxidizing.

Before boiling the solution is a clear/greenish tint.
But as I'm boiling the water off at about 50% I see a rapid shift to very dark green. Almost black.

Right or wrong it's doing something.

Oh and thanks for going easy on me, Dick.


White cloudy junk: zinc hydroxy chlorides.

Green: clearly a contamination, all of Zn (II) cations are colourless. Green could point to copper or iron.

Fast boiling that solution is likely to lead to hydrolysed mass of various indistinguishable zinc hydroxy chlorides.

dchainy - 14-6-2012 at 09:18

Now that's more like it.

Thanks.

dchainy - 14-6-2012 at 13:29

Hey guys, is there's a way to post pix of the crap I'm making?
Or should I post a link to my pix on facebook?

Oh BTW the initial sol is clear. Only a slight hint of green.

blogfast25 - 15-6-2012 at 05:07

Quote: Originally posted by dchainy  
Hey guys, is there's a way to post pix of the crap I'm making?
Or should I post a link to my pix on facebook?

Oh BTW the initial sol is clear. Only a slight hint of green.


Look in the FAQ, You can insert or upload pix in various ways here.

S.C. Wack - 15-6-2012 at 19:02

I happen to have made a solution of ZnCl2 this week, for activated charcoal experimentation, but anyways -
There should not be green or white anything; Zn should dissolve nicely until any remaining HCl has no more power to dissolve any more, resulting in a clear colorless solution above undissolved zinc. I have legit Zn powder but am more familiar with powder from alkaline batteries, and molten old D cell casings; IME the more exposure to air especially as powder, the more gray whatever insoluble in HCl.

So the usual SM story then. I guess more HCl could be added to the white whatever but if that doesn't make ZnCl2 you're SOL.

dchainy - 15-6-2012 at 19:08

I think my green tint is from using Muriatic Acid (polluted) rather than pure HCl.

Otherwise from the books I have here I think I'm on the right track. I even did the H2S trick and dropped ZnS.

Go figure.

S.C. Wack - 15-6-2012 at 19:15

My HCl was yellow-green hardware store product too. The green went away.

blogfast25 - 16-6-2012 at 04:38

Aaaahh, so it is iron (the green). Most technical HCl (aq) contains some Fe3+, easily shown with thiocyanate (KSCN or NH47SCN). Zinc however plates out Fe:

3 Zn + 2 Fe3+ === > 3 Zn2+ + 2 Fe

In these acid conditions the reduction only goes to Fe (II):

Zn + 2 Fe3+ === > Zn2+ + 2 Fe2+

... which is green (ferrous ion hydrated).

But post-dissolution, the Fe2+ is easily air oxidised back to Fe3+, which in acidic conditions and low concentration is yellow. And at really low concentration almost invisible.

Pure ZnCl2, as ZnSO4, is snow white.

Which reminds me of a similar ‘mini-mystery’ when I obtained distinctly green solutions when dissolving pewter (Sn/Sb alloys) in conc. HCl. Here the culprit turned out not to be iron from the HCl, but Cr in the pewter, although what it was doing there I still do not know to this day…


[Edited on 16-6-2012 by blogfast25]