August 24, 2019, 06:33:02 PM
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Topic: Tips for preparing crystals of nickel(II) chloride hexahydrate?  (Read 265 times)

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Offline Arcaeca

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So I'm trying to make oil paints from scratch just for my own amusement, using boiled linseed oil as the vehicle and a bit of chemistry to make the pigments, inc. copper(II) acetate for blue, an indeterminate mixture of iron(III) oxides and acetates for orange, etc.

Well, I seized upon the idea of trying to prepare nickel(II) chloride hexahydrate, not just because it's a brilliant green on its own, but also because - as I understand - it can be mixed with a stoichiometric excess of ammonia to form a deep bluish-violet ammine complex.

So I have a mason jar (can't afford anything borosilicate) that I put a couple nickel-plated countersunk finishing washers which I thought were brass underneath and covered with ~32% HCl (MSDS); later I stumbled upon this blog post about making NiCl2·6H2O, which was using more or less the same process I was except with US $0.05 coins (which I didn't know were part nickel), which turned out to be something like 20x more cost-effective than buying finishing washers, so I chucked a couple nickels in the mason jar too. I also started a second mason jar with more nickels and HCl.

Well, after leaving them to dissolve for about a week, the 1st jar (washers + coins) was a dull, dark green and had flecks of undissolved but solid metal floating in it, while the 2nd gar was a more vibrant green with no precipitate. After decanting liquid part of the 1st jar, careful not to get any of the flakes into the new jar, and leaving it uncovered overnight to start evaporating, it turned... nearly black, with a slight amber tinge. This makes me suspect the metal underneath the nickel plating on the washers was iron (oxidized from Fe+2 to Fe+3 overnight) all along, not brass, especially since the washers dissolved entirely and the coins (75% copper, 25% nickel, but no iron) didn't.

And that's where we are now.

The black-amber liquid from the 1st jar is still apparently acidic enough to react with aluminum, so I can't put it in an aluminum foil pan to speed up the evaporation process like the copper acetate or rust from before (plus it fumes slightly). The blog post from before instructed to boil the remaining liquid off, but I don't think my non-borosilicate mason jars could tolerate that kind of heat (one broke before over direct flame); I have a propane camp stove and stainless steel pot to decant them into, but after seeing what the solution did to the foil pan... I'm hesitant, not least of which because I want less iron in solution, not more.

So:
  • Can the 1st jar be salvaged, i.e. by removing the iron? (Precipitating it out with oxalic acid as iron(III) oxalate, perhaps?)
  • If the problem with the 1st jar wasn't iron to begin with, how can I avoid ruining the 2nd solution and turning it the wrong color as well?
  • What method is most likely to produce good green crystals without destroying my equipment or killing me?

(Safety and equipment notes: I'm doing all of this outside, which is about as "well-ventilated" as you can get without a fume hood, and on concrete instead of directly next to vegetation or anything flammable. I wear a dust mask and chemical-resistant gloves and goggles when handling the solutions, but I have essentially no other laboratory equipment whatsoever and, as mentioned before, use mason jars because I have no borosilicate beakers. All my raw materials are consumer-grade, by which I mean they're of low enough concentration and volume that you can get them at most hardware stores.)

Last note: since I'm new to the forums, I'm not sure if this is the right board or it should've gone in Undergraduate (which I am, but ChemE major instead of Chem, and this isn't homework or anything) or Inorganic. I'll probably also cross-post this to a couple other forums besides Chemical Forums since I'm not sure how active this place is.

Online billnotgatez

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Re: Tips for preparing crystals of nickel(II) chloride hexahydrate?
« Reply #1 on: August 12, 2019, 04:20:37 AM »
...
Last note: since I'm new to the forums, I'm not sure if this is the right board or it should've gone in Undergraduate (which I am, but ChemE major instead of Chem, and this isn't homework or anything) or Inorganic. I'll probably also cross-post this to a couple other forums besides Chemical Forums since I'm not sure how active this place is.

no cross posting on our forum
This is a forum policy.
Click on the link near the top center of the forum page.
Forum Rules: Read This Before Posting.
http://www.chemicalforums.com/index.php?topic=65859.0

I think
Citizen Chemist
is probably the best place for this post.

Online billnotgatez

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Re: Tips for preparing crystals of nickel(II) chloride hexahydrate?
« Reply #2 on: August 12, 2019, 04:28:35 AM »
If I remember Mason jars are used in canning where they are submerged in boiling water. Test a Mason jar with just water will work using something like a sand bath, thermometer and hot plate will work.

https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Book%3A_Organic_Chemistry_Lab_Techniques_(Nichols)/1%3A_General_Techniques/1.3%3A_Heating_and_Cooling_Methods/1.3H%3A_Water%2C_Sand%2C_and_Oil_Baths

Offline Arcaeca

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Re: Tips for preparing crystals of nickel(II) chloride hexahydrate?
« Reply #3 on: August 12, 2019, 09:18:55 PM »
Quote
no cross posting on our forum
Right, which is I why I meant I was going to cross post to other forums, i.e., on other websites besides CF.

Anyway, I got my hands on some oxalic acid (pKa 1.25, 4.14) and NaOH (pKa 14.56) which I combined dissolved in ~100 mL of water each and combined in a roughly 1:2 ratio to produce a solution of sodium oxalate hopefully close-ish to neutral (I don't have a pH probe). Adding this to the amber/black solution caused it to clear up and turn back to the vibrant green of a NiCl2·6H2O solution, as I suspected, but I also expected iron oxalate to precipitate out as a yellowish solid, and there was no precipitate and no cloudiness.

(Technically what I did was combine oxalic acid (aq) and NaOH (aq) in a roughly 1:1 ratio, added it to the black solution, it turned green but no precipitate, went back to my computer and looked up how to make sodium oxalate and apparently you need a 1:2 acid:base ratio, not 1:1, and that what I actually made was sodium hydrogenoxalate, so I made another batch of ~100 mL of NaOH (aq), added it to the now-green solution, still green and still no precipitate)

Offline Borek

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Re: Tips for preparing crystals of nickel(II) chloride hexahydrate?
« Reply #4 on: August 13, 2019, 03:00:55 AM »
Try to buy universal pH strips, they are cheap.

Precipitates won't show before you get past the solubility limit of a given salt or hydroxide (actually it is about getting past the solubility product, but let's keep things simple).

Oxalate is a good complexing agent, it complexes both iron and nickel. Iron complexes are much more stable, so my bet is that's what happened - you complexed iron.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Enthalpy

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Re: Tips for preparing crystals of nickel(II) chloride hexahydrate?
« Reply #5 on: August 13, 2019, 06:28:45 AM »
Linseed oil is unhealthy.

It is one thing that made 19th century painters mad (the others being absinthe and alcohol).

Please be careful for real!

Offline Arcaeca

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Re: Tips for preparing crystals of nickel(II) chloride hexahydrate?
« Reply #6 on: August 14, 2019, 12:28:00 AM »
I apparently forgot oxalate can be a ligand. In that case, I guess it's likely that the green solution w/out precipitate was largely sodium ferrioxalate.

I prepared a sort of makeshift sand bath as suggested by placing the mason jar in a galvanized steel bucket and surrounding the jar on all sides + bottom with sand, and placing the whole bucket on top of a single-burner propane camp stove. I boiled most but not all of the water off (perhaps 2/3 - 3/4 of the water), but during the heating process the solution turned amber-colored. I left it to cool over night to see if it returns to green when cooled, but if not, I have no idea what I just made.

Aaaaanyway since this is veering a bit far from the original goal of making nickel chloride - the 2nd batch of nickel chloride (the one uncontaminated with iron) looks about saturated (i.e. not getting any greener); is it actually safe to boil the liquid off in a sand bath, since the fumes would contain a fair amount of HCl (g)?

Online billnotgatez

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Re: Tips for preparing crystals of nickel(II) chloride hexahydrate?
« Reply #7 on: August 15, 2019, 03:34:42 PM »
You said you are doing this outdoors and not standing downwind and not near anyone or anything that can be harmed?

Offline Arcaeca

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Re: Tips for preparing crystals of nickel(II) chloride hexahydrate?
« Reply #8 on: August 17, 2019, 02:11:26 AM »
Ehhhhh... outside, yes, and if I boil it off during the night there won't be anyone else around but me to breathe in the fumes, but I don't know how to guarantee not standing downwind of it except by, say, going indoors to watch from a window until the fuel runs out.

(I decanted the saturated green NiCl2 solution and it turned extremely dark, almost black, overnight. Here's to hoping that's just absorbing moisture from the atmosphere, because if it's anything else I have no idea what happened or how to fix it)

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