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Author: Subject: Dissolving germanium metal
Mixell
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[*] posted on 20-2-2011 at 10:08
Dissolving germanium metal


I've tried dissolving germanium powder with various acids, nothing worked so far.
The following mixtures and acid were used:
concentrated nitric acid (and later hydrogen peroxide was added).
concentrated sulfuric acid (and later hydrogen peroxide was added).
and Aqua Regia wish has proven to dissolve the germanium, but extremely slowly (the other solutions were completely useless).
The experiment was done at ~40C.

Can anyone suggest a substance that could efficiently dissolve germanium?
Maybe I can try heating the aqua regia to 60-90 C (although that will speed up the harmful gas production)?
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[*] posted on 20-2-2011 at 10:44


Trying to dissolve germanium in acids is a bit like trying to dissolve carbon or silicon in acids: as useless as trying to fit wheels to a tomato.

Germanium isn’t, despite its deceptive appearance, a metal. It’s a metalloid (‘half-metal’, if you prefer) and behaves more like a non-metal than an actual metal.

Germanium can be dissolved by fusing with alkalis, possibly also slowly by reacting with very hot, very concentrated (50 %) NaOH or KOH, resulting in the analogs of carbonates and silicates, the germanates: GeO3(2-). In the presence of water these should promptly hydrolyse to GeO2.

Wiki states that it dissolves slowly in conc. H2SO4 but I'm betting all you'll get from that is insoluble GeO2... Hot aqua regia will also produce GeO2 (at best).

Forget about making conventional salts from germanium: most compounds in the prevalent IV oxidation state are non-ionic (see halides, e.g.) and easily hydrolysed back to GeO2...

Where did you obtain the germanium?


[Edited on 20-2-2011 by blogfast25]
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[*] posted on 20-2-2011 at 10:52


After you've obtained GeO2 by acidification of a germanate solution, this can be reacted with saturated aqueous HCl and GeCl4 distilled off. This is an important contrast to the homologous SiCl4, whose hydrolysis to SiO2 is irreversible.



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[*] posted on 20-2-2011 at 10:56


Aqua Regia is starting to show some result when heated to 50-70C (it dissolves a few miligrams in 20 mins, noticeable but useless).
I've also tried burning germanium to get some germanium oxide and dissolving it in water to get germanic acid (H4GeO4), the quantities here were also extremely tiny, I didn't find the time to test the solution for pH, maybe I will do it in a few days.
The germanium was given to me by my granfather (he was a chemistry professor at a zinc production plant (that also contained a research laboratory) in Soviet Russia.
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[*] posted on 20-2-2011 at 10:59


Quote: Originally posted by garage chemist  
After you've obtained GeO2 by acidification of a germanate solution, this can be reacted with saturated aqueous HCl and GeCl4 distilled off. This is an important contrast to the homologous SiCl4, whose hydrolysis to SiO2 is irreversible.


Are you sure of this? Wiki mentions that but it also mentions how easily the tetrahalides are hydrolysed. The two statements seem highly contradictory to me…
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[*] posted on 20-2-2011 at 11:02


Quote: Originally posted by Mixell  
The germanium was given to me by my granfather (he was a chemistry professor at a zinc production plant (that also contained a research laboratory) in Soviet Russia.


Lucky you! Ge is indeed the by product of several metal smelter's 'fly ash'. Some fly ashes from certain types of coal also contain Ge...
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[*] posted on 20-2-2011 at 11:11


Aqua regia will work, as will strong hydrobromic acid with the slow addition of Br2; in either case it needs to be 5060 C, and done under reflux to avoid loss of the tetrahalide as noted by garage chemist. In analytical chemistry this was a method of separating Se, As, Ge, and sometimes Sb, from other metals. Hot sulfuric acid does work, but is quite slow.

Hot concentrated NaOH solution, or molten NaOH - add Ge __slowly__- is a better method.

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[*] posted on 20-2-2011 at 11:32


Brauer gives a method for GeCl4 from GeO2 and HCl, but it is found as part of the GeO2 preparation.
GeO2 is mixed with conc. (37%) HCl and very slowly heated and distilled. If As is present as an impurity, a slow stream of chlorine has to be bubbled in to oxidise it to arsenic acid and prevent volatilization as AsCl3.
A biphasic distillate collects, the upper layer is 20% aqueous HCl. The layers are separated and the lower one is poured into a large volume of ice, shaken, and left to stand over night.
GeO2 precipitates and is filtered, from the acidic supernatant, dissolved Ge is precipitated as GeS2 with H2S.

Also, methods for reclaiming Ge from residues are given.
Elementary Ge is best worked up by chlorination with Cl2 at 450-500°C followed by hydrolysis of the GeCl4.
GeO2 easily dissolves in aqueous alkali, from the acidified solution, GeS2 can be precipitated by gassing with H2S. Precipitation as GeS2 is the best method to work up dilute aqueous Ge solutions.




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[*] posted on 20-2-2011 at 13:21


@Blogfast: You can get germanium from Ebay as IR lenses
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[*] posted on 20-2-2011 at 13:41


Quote: Originally posted by Eclectic  
@Blogfast: You can get germanium from Ebay as IR lenses


You can also get it from ebay as germanium.




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[*] posted on 22-2-2011 at 06:01


Is it possible to extract sodium germanate (Na2GeO3) from a solution of NaOH?
And how do I exactly extract the solid GeO2 from a germanate solution?
Slowly adding acid until the germanium dioxide precipitates out of the solution?
I assume the reaction between germanium and sodium hydroxide is as following:
2NaOH +Ge +H2O ---> Na2GeO3(aq) + 2H2 ?
Or the reaction may be more complex with varying products depending on the exact conditions?
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[*] posted on 22-2-2011 at 10:20


Quote: Originally posted by Mixell  
Is it possible to extract sodium germanate (Na2GeO3) from a solution of NaOH?
And how do I exactly extract the solid GeO2 from a germanate solution?
Slowly adding acid until the germanium dioxide precipitates out of the solution?
I assume the reaction between germanium and sodium hydroxide is as following:
2NaOH +Ge +H2O ---> Na2GeO3(aq) + 2H2 ?
Or the reaction may be more complex with varying products depending on the exact conditions?


Just gently acidify the solution of germanate (with excess NaOH) until the white GeO2 drops out. Actually isolating the germanate may not be possible because it's so sensitive to hydrolysis.

The balanced reaction is correct: 2NaOH (aq) + Ge (s) + H2O (l) ---> Na2GeO3 (aq) + 2H2 (g). No other reaction products can form as far as I know...
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[*] posted on 22-2-2011 at 12:29


According to wikipedia, GeO2 can be dissolved in water to give germanic acid (H4GeO4).
May be it is possible to add NaOH to a solution of germanic acid (with a proper mole ratio) and get Na4GeO4? Could be very interesting to try this.
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[*] posted on 22-2-2011 at 12:45


Quote: Originally posted by Mixell  
According to wikipedia, GeO2 can be dissolved in water to give germanic acid (H4GeO4).
May be it is possible to add NaOH to a solution of germanic acid (with a proper mole ratio) and get Na4GeO4? Could be very interesting to try this.


Not in my version, it doesn’t.

Mine says:

”The dioxide, GeO2 can be obtained by roasting germanium sulfide (GeS2), and is a white powder that is only slightly soluble in water but reacts with alkalis to form germanates.”

http://en.wikipedia.org/wiki/Germanium#Chemistry

Think periodic table of the elements: SiO2 is completely insoluble in water, soluble only in HF or alkalis (but with great difficulty), SnO2 is completely insoluble in water and acids, but soluble in very hot, concentrated alkalis (and can be fused with them to form stannates). What in your book should make GeO2 any different???
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[*] posted on 22-2-2011 at 12:51


Well, so it possible that the information given in wikipedia is wrong, but here it is:
"The rutile form of germanium dioxide is more soluble than the hexagonal form and dissolves to form germanic acid, H4GeO4 or Ge(OH)4."

http://en.wikipedia.org/wiki/GeO2
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[*] posted on 22-2-2011 at 13:00


'dissolves' is fairly non-specific: no actual solubility numbers are given. I suggest you treat even freshly precipitated GeO2 with water and you will find that 'insoluble in water' is probably an apt term...
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[*] posted on 22-2-2011 at 13:03


Numbers are given:
5.2 g/l (25 °C)
10.7 g/l (100 °C)

Its quite minute, but its something.
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[*] posted on 22-2-2011 at 13:40


5.2 g/l at RT that's 0.5 %. More than I would have given it credit for.

But why do you want a solution of Ge(OH)4?
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[*] posted on 22-2-2011 at 13:46


I would like to try to isolate some of its salts, if its possible of-course, could be quite interesting to see what properties they have (would be even better to find some information on them, but I didn't manage to do so).
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[*] posted on 22-2-2011 at 14:30


Well, more or less forget about salts in which Ge plays the tole of cation. But maybe Na2GeO3 can be isolated, who knows? Dissolve some freshly precipitated GeO2 in an exact equivalent amount (acc. the reaction equation you wrote) of quite concentrated NaOH or KOH (allow for plenty time and stirring), filter off any turbidity and gently evaporate. If the product is crystalline and redissolves in pure water it's likely to be a germanate.

Or ice the solution, instead of evaporating...

[Edited on 23-2-2011 by blogfast25]
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[*] posted on 23-2-2011 at 23:47


I don't believe the numbers in Wikipedia. I have 50 grams of GeO2 and did quite a few experiments with this. It does not dissolve in water, at least not visibly. If it really could dissolve in water at 10 grams per liter, then I would be able to dissolve a spatula full of this solid in 100 ml of water. No, it doesn't. I am inclined to think that the numbers in the Wiki page must be in mg/liter.

In conc. HCl indeed quite some GeO2 can be dissolved. It dissolves slowly, but I managed to dissolve several 100's of mg in a test tube containing 10 ml of acid. When this solution is diluted, then the liquid becomes milky/opaque and a very fine white precipitate settles at the bottom.




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[*] posted on 24-2-2011 at 08:51


Sounds plausible, Woelen. I'm very skeptical about GeO2 being even slightly soluble in water: see SiO2 and SnO2...

[Edited on 24-2-2011 by blogfast25]
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[*] posted on 24-2-2011 at 09:59


It seems that there is a soluble form and an insoluble form, also solution is achieved by boiling under reflux for some time!

http://www.krasgermanium.com/products?article=prod20

and

http://www.teck.com/DocumentViewer.aspx?elementId=115437&...

Try a search on solubility germanium dioxide.

Material scientists, right cards!
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[*] posted on 24-2-2011 at 12:41


The combined solubility data from both sources are 1 g/100 ml at RT, 4.5 g/L at 25 C and 10.7 g/L at 100 C. Hardly a testimony to solubility, in my book...
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[*] posted on 24-2-2011 at 17:10


I have that same problem with Ge...

I attach two publications were trying to dissolve Ge...



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