LHcheM
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Strange result with reduction with KBH4?
I recently did some colloidal gold experiments, which I reacted auric acid in HCl, and KBH4 in KOH, the results I obtained is not a red "solution" as
wiki said (Martin's method), but lumps of blue-black precipitates of gold... Can anyone suggest why?
Also I did the same to silver nitrate in nitric acid; copper nitrate in nitric acid, for copper, with a lot of fizzing, dull yellow precipitate of
copper metal appeared instantly after the addition of KBH4, but for silver, there's a somewhat different result, as after the addition of KBH4,
there's alot of fizzing accompanied by the formation of a black gelatinous precipitate, and upon standing the black ppt turns into a white, fine
precipitate which is very light. Can anyone suggest an explanation for this?? Thx~
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Adas
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This looks very interesting, but I have no idea what it is :X
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kavu
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When it comes to fine particles of anything suspended in a solution the color is greatly dependent on the particle size. Fine particles of gold for
example appear red and as the particle size grows the color shifts towards blue. This is due to diffraction of white light. It is in generally quite
hard to synthesize a particle of a given size. You might for example try adding the borohydride in a tad slower, agitating the mixture more or
changing the temperature of the mixture.
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BromicAcid
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Make sure you follow the established procedure exactly, when I did these sorts of experiments in college it took precision with an analytical balance
and decent quality reagents. In this way we were able to make a whole spectrum of colloidal gold solutions, temperature, mixing rate, and even the
total ionic character of the solution can greatly affect the aggregation of these particles. Nevertheless, I have seen enough examples where people
have successfully made these solutions in their own home to know that following the directions to the letter is probably the most important part of
all.
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LHcheM
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@BromicAcid
You made a whole spectrum of colloidal gold solutions!? 0.0 Can you please give me some information about your experiments you did in your college?
Because I can't find those information on the web about these factors (especially ionic character). Well I'm just in Secondary Schools and don't have
the chance...
I follow this procedure: http://www.youtube.com/watch?v=nqkwM9o1s-w
So maybe I will try using the same principle to prepare colloidal silver~
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AndersHoveland
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You do realise that an alkaline solution of H2O2 can also be used to reduce HAuCl4 ?
(2)AuCl4[-] + (3)H2O2 + (6)OH[-] --> (2)Au + (8)Cl[-] + (6)H2O + (3)O2
The gold usually separates out in a finely divided state, and appears brown by reflected light and greenish blue by transmitted light. If very dilte
solutions are used, the gold sometimes separates out forming a yellowish film on the sides of the test tube.
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LHcheM
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Really!? I'll try that right now!
Thanks~
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LHcheM
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Well have just tried with H2O2, it produced a blue-black solution (I used very dilute AuCl3 this time), maybe the size of the gold particles are large
so that the color of solution is blue (not red?)
I tried with SnCl2 in conc HCl as well, and I obtained a purple solution instead, I used the same concentration of AuCl3 for both experiments, but
still I can't accomplish the ruby-red solution of colloidal gold...
is it because my AuCl3 is not conc enough? I used about 0.1M each time
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AndersHoveland
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HAuCl4 solutions can also be reduced with elemental phosphorous, which forms transparent red or blue solutions of colloidal gold. These brilliant
colors can only be seen with transmitted light (hold the test tube up against a light source and look through the tube at the light). The solution
appears to be only a murky brown by reflected light.
"A short manual of chemistry" p190
August Dupré, Henry Wilson Hake
Have you ever heard of the "Purple of Cassius" ?
from wikipedia: "The tin(II) chloride reduces the chloroauric acid from the dissolution of gold in aqua regia to a colloid of elemental gold supported
on tin dioxide to give a purple precipitate or coloration."
Go to the bottom of the page to see a picture of the characteristically purple solution: https://sites.google.com/site/ecpreparation/explosive-metal-...
[Edited on 7-11-2011 by AndersHoveland]
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LHcheM
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I have alot of phosphorus at hand, but it's red phosphorus, would it work? or should I just dump it into the solution?
All my solution have a color of purple-blue when viewed through transmitted light ...
Yep I've heard of that, from Inorganic Chemistry, by Catherine E. Housecraft, unfortunately this is the only piece of info the book provided about
colloidal gold
Thanks for the website~ ^^
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