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Kitsune
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Dissolution of Group 6 metals
Hi all, this is my first Post on this forum. Recently I have decided to look at the compounds of certain Transition metals, namely those of Group 6
(Tungsten and Molybdenum).
From my research I see that both Tungsten and Molybdenum, at least for the home chemist are very difficult to put into solution. I happened across a
few different scientific papers (sadly most abstract only) which eluded to the use of Hydrogen peroxide to dissolve Molybdenum; unable to find any
more research I set about testing the theory that these metals though invulnerable to the Hydrochloric, Sulphuric and Nitric acids nor the bases,
could be put into solution by Hydrogen Peroxide.
My Method was as follows:
Taking a small piece of clean Molybdenum wire (salvaged from old Incandescent light bulbs that were no longer needed) I placed this into a solution of
5cm3 6% Hydrogen Peroxide (due to where I live, this is the most concentrate Solution available) and 5cm3 of 1M Acetic acid.
Right away the very fine ends of the wire where it had been cut started to form few bubbles, heating this solution weakly the few bubbles increased to
a continuous stream, after one day, the wire had disappeared into solution, leaving a rather fetching lemon yellow hue.
I have been allowing this solution to sit and evaporate, it is currently at about 5cm3
I have also done this with Tungsten also recovered from an old incandescent bulb (filament) which also dissolved, slightly faster. I am soon going to
be testing this also on the group 5 metal, Tantalum due to it's similar chemistry.
The idea of using Acetic Acid along with the Hydrogen peroxide came from the standard route for making Transition Metal Acetates from the metal such
as Copper Acetate.
My Question is, what are the products likely to be from these reactions, which oxidation state am I looking at, what intermediate compounds were there
(product of Hydrogen Peroxide on the metal) and whether they are likely to decompose when out of solution (upon crystallisation).
My original thoughts were Dimolybdenum (ii) Tetraacetate (the colour in solution would support this) and Ditungsten (ii) Tetraacetate though with
these metals, but I'm not sure. Anyway, all suggestions welcome.
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j_sum1
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Cool work. Nothing much to add except to say I intend to try this too.
Following this thread for more info.
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AsocialSurvival
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They form soluble molybdate and tungstate with bases like Sodium Hydroxide.
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Justin Blaise
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You may have already seen this paper, but it looks like you can get pertungstic acid if you crystallize and dry the compound at <100 degrees C,
tungstic acid at temperatures around 180 degrees C, and tungsten trioxide at higher temperatures. It also appears that acetic acid is unnecessary, as
H2O2 will do the job on its own.
Attachment: tungsten hydrogen peroxide.pdf (281kB)
This file has been downloaded 920 times
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Mesa
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Said bases are precursors to some pretty interesting heteropoly acids(silico/phosphotungstic acids.)
Also to note, H2WO4 decomposes to WO3 after a short duration, becoming insoluable/precipitating from solution.
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Kitsune
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Thank you for the paper Justin, I read the first half of it previously (only a preview was available), It is pretty interesting stuff and worth trying
out, if only for the yellow of the molybdenum+2 ion in solution.
An update: Today I got a little impatient as I have been waiting the solutions to crystallise out for several weeks now; I set about gently heating
the solutions.
The Molybdenum solution: yielded an equally as beautiful as before, lemon yellow compound which when heated to decomposition evolves a vapour with an
acetic scent; I guess I managed to form Dimolybdenum (ii) Tetraacetate, of which I later decomposed to Molybdenum (vi) Trioxide.
The Tungsten solution: a white solid which upon stronger heating decomposed to a yellow solid with no acetic off gas, Tungsten (vi) Oxide would be my
guess.
I will reproduce these reactions, when I get the time and then try to form alkali metal molybdates and tungstates (Sodium Molybdate and Tungstate at
first), then Tungsten Carbide will likely become a targeted source of tungsten for dissolution, from no less than dead ball point pens (ball points).
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Justin Blaise
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No problem. If you have any other references you can't access, I'll see if my university has a license with the journals. I'd love to read more on
this stuff.
Also, how much tungsten and molybdenum do you get out of each light bulb?
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Kitsune
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Thanks for the offer, I may need to take you up on that sometime.
The amount and quality of what you can get from an incandescent light bulb is variable; it depends on the size, make, construction, whether it is new
or used. (Remember that the large wires on each end of the filament are not Molybdenum, it's only the small silver ones that are in the middle)
That all said, the Molybdenum experiment used one filament support (usually you will get two or three per bulb), this was enough for proof of concept
and I also ended up with 250mg of compound for good measure.
The Tungsten reaction used only one rather small length of filament (sometimes they snap during recovery from the bulb) and this yielded just as well
as the Molybdenum, though it did not form an Acetate but Tungstic acid.
A better source of the WO4 2- Ion may be Tungsten Carbide, a cheap source would be ballpoint pens (if you can cope with the ink you will need to
repetitively wash from them beforehand), the Tungsten filament is an incredibly fine wire, wound into a single or double coil for greater surface area
so you never get too as much material as you think you have. At this time, I have yet to test whether the WC/W2C approach is valid for a home chemist.
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MrHomeScientist
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It's been mentioned before on the forum that tungsten can be dissolved into pertungstic acid, tungstic acid, or tungsten trioxide (depending on drying
temperature) by dissolusion in 30% H2O2: http://www.sciencemadness.org/talk/viewthread.php?tid=395
Something I definitely want to try at some point. I didn't know that molybdenum was also susceptible to peroxide.
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Mesa
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Tungsten also makes an interesting thermite with KNO3/NaNO3, however NaOH/W mixtures merely melt and bubble.
The KNO3/W mixture leaves a black residue weighing less than the original amount of tungsten(I assume a volatile tungsten salt is one of the products
of the thermite reaction.) and dissolves in hydroxides.
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j_sum1
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Let's see if I have this right Mesa.
You mix together a stoichiometric ratio of W and KNO3 for your thermite. Ignite and watch the fun. And the reaction products are... Does this form
potassium?
(Runs off to break a million light bulbs and scavenge for the filaments...)
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elementcollector1
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Doubtful - at most, it's likely potassium oxide. Was the dissolution particularly vigorous?
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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Mesa
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I have no idea what it forms. It looks a lot like a fused salt(i.e. similar texture to fused KNO3 I tried to reduce with carbon a few times) and is a
very dark grey/black colour. The reaction itself is very fast and produces a remarkably bright white flame, I assume that indicates it's a lot more
exothermic than other thermites(based on very little evidence admittedly) so any potassium formed likely evaporates instantly.
Edit: I'm not sure if this would work with lightbulb filaments. I pillaged around 3kg of tungsten powder from a precision engineering company my
father used to work for. The powder is about as fine as sifted flour.
[Edited on 16-10-2014 by Mesa]
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j_sum1
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I wasn't serious about the potassium or the lightbulbs. But interesting thermites are always, well, interesting.
My next element order is likely to be both tungsten and and molybdenum. Not really sure I want to be flaring it away. But a teeny bit of
experimentation might be fun.
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Mesa
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If you want I can do another small KNO3/W ignition and take pictures of the process/aftermath. I don't currently have a camera/mobile but I can get
one later on today.
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j_sum1
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Cool. Please do. Video too if you are able.
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blogfast25
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Quote: Originally posted by Mesa  | Tungsten also makes an interesting thermite with KNO3/NaNO3, however NaOH/W mixtures merely melt and bubble.
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You shouldn't call that 'thermite'. It's simply an oxidation of tungsten with saltpetre. The product, mainly WO<sub>3</sub>, is black due
to unreacted W and may be some lower oxides.
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Dan Vizine
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Here's something you might enjoy j_sum1, all the thermite, intermetallic & metal combustion info you could want.
Attachment: Survey of Combustible Metals.pdf (9.8MB)
This file has been downloaded 629 times
[Edited on 24-10-2014 by Dan Vizine]
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j_sum1
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Fantastic. I think. I have tried downloading but the pdf seems corrupted. Would you care to upload again?
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Dan Vizine
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| Quote: Originally posted by j_sum1 | | Fantastic. I think. I have tried downloading but the pdf seems corrupted. Would you care to upload again? |
Let me try again....
Attachment: Survey of Combustible Metals.pdf (9.8MB)
This file has been downloaded 615 times
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j_sum1
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Whoa. Pages of fun.
Lots of interesting reactants to get.
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j_sum1
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I have just attempted dissolution of Mo wire in 6% H2O2 and dilute acetic acid. (Mo sourced online as a cutting tool for mobile phone repair)
Test tube scale -- approximately 600mm of wire (0.11mm diameter) with around 5mL of peroxide and a slightly smaller amount of vinegar.
Progress is really slow. It has been bubbling away for nearly 24 hours so far and it is hard to see much change. The wire does appear thinner and
has lost its lustre. The solution has a yellowish tinge -- interestingly near the top. After shaking the solution appeared clear (presumably from
dilution). However, a couple of hours later the yellowish colour appeared at the top again. I guess the reaction products are transported upwards
with the bubbles.
I'd like to attempt this again with stronger peroxide and without the acetic acid. I also have some tungsten to try.
The colour is an interesting subtle gold hue and rather nice.
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Kitsune1
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It really is a slow reaction, my aim was to make an acetate of Molybdenum by first oxidising the metal, then forming an acetate; it does (like the
Tungsten) dissolve in H2O2, a higher strength makes it react quicker, though not that much quicker, I'm glad I only used
incandescent light bulb filament supports, they took long enough but the colour is quite nice.
OP was my old account, couldn't log in and then never received an email to change my password (checked spam, resubmitted so decided I'd just make this
account instead).
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j_sum1
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| Quote: Originally posted by Kitsune1 | | OP was my old account, couldn't log in and then never received an email to change my password (checked spam, resubmitted so decided I'd just make this
account instead). |
I figured that.
I need to do a bit more research on this one. I am hazy about the reaction products including the bubbles that come off the wire.
I mainly did this as a little sideline while I spent a couple of hours tidying the lab and also to test that what I had bought was indeed Mo or
predominantly so.
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Mesa
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Reaction products are O2 and H2MoO4.
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