pichoro
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Trouble with a Dilution Plan for Gold(III) Chloride
Hi, curious if anybody could give me a hand with this?
I'm trying to come up with a plan for diluting 0.25 g of Gold(III) Chloride to approximately 0.001 M (preferably a little over rather than a little
under) using volumetric glassware.
I'm trying to recreate this, but using 0.25 g instead of 1 g as it is considerably cheaper, yet will still last me a ridiculously long time at the
slow rate I'll use it: http://education.mrsec.wisc.edu/nanolab/gold/index.html
I plan on buying 0.25 g from Alfa Aesar. They do not mention any waters of hydration in their formula, and report a formula weight of 303.33 g/mol,
leading me to believe it is anhydrous, or they're full of crud. https://www.alfa.com/en/catalog/12163
I can access most any size volumetric pipet or flask, up to like 50 mL pipets and 2000 mL flasks.
The original instructions call for diluting the full 1 g of gold(III) chloride trihydrate in 250 mL of solution for a molarity of 0.01 M, then
diluting 25 mL at a time out to 250 mL for make the 0.001 M.
I'd like to offer some starting point I'm at, but I've honestly had no real success figuring something out for this. I may yet end up using an
analytical balance to divide it up between a 500 mL volumetric and a 250 mL volumetric, if nobody has any advice. 
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DraconicAcid
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The original instructions will give you a concentration of 0.0013 M.
If you dissolved 0.2 g of the gold chloride in 50 mL solution, and then did the same 25 mL -> 250 mL dilution, (or just dissolved it straight into
a 500 mL volumetric flask) then you would get the same concentration, and have 0.05 g gold(III) chloride left.
[Edited on 12-5-2014 by DraconicAcid]
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Zyklon-A
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Question about gold (III) chloride
| Quote: | Originally posted on Wiki
Preparation:
Gold(III) chloride is most often prepared by passing chlorine gas over gold powder at 180 °C:[1]
2 Au + 3 Cl2 → Au2Cl6
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Then:
| Quote: | Originally posted on Wiki
Anhydrous AuCl3 begins to decompose to AuCl at around 160 °C; however, this in turn undergoes disproportionation at higher temperatures to
give gold metal and AuCl3.
AuCl3 → AuCl + Cl2 (>160 °C)
3 AuCl → AuCl3 + 2 Au (>420 °C)
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Anyone see the problem? My guess is, in an atmosphere of chlorine, the reaction equilibrium stays on the left even past the temperature where it
normally decomposes ?: AuCl3 → AuCl + Cl2
[Edited on 12-5-2014 by Zyklonb]
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pichoro
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Quote: Originally posted by DraconicAcid  | The original instructions will give you a concentration of 0.0013 M.
If you dissolved 0.2 g of the gold chloride in 50 mL solution, and then did the same 25 mL -> 250 mL dilution, (or just dissolved it straight into
a 500 mL volumetric flask) then you would get the same concentration, and have 0.05 g gold(III) chloride left. |
My problem being that the 0.05 g won't remain in a quantitatively useful form for long as it is hygroscopic. It is recommended by the procedure for
this demo to dissolve all of the gold(III) chloride, even the trihydrate form, to prevent this from being an issue. If they're actually selling
anhydrous gold(III) chloride, it will quickly be not so anhydrous. I guess I just remember that there should be 0.05 g left? Make a note, and hope
the package was right?
| Quote: Originally posted by Zyklonb | | Quote: | Originally posted on Wiki
Preparation:
Gold(III) chloride is most often prepared by passing chlorine gas over gold powder at 180 °C:[1]
2 Au + 3 Cl2 → Au2Cl6
|
Then:
| Quote: | Originally posted on Wiki
Anhydrous AuCl3 begins to decompose to AuCl at around 160 °C; however, this in turn undergoes disproportionation at higher temperatures to
give gold metal and AuCl3.
AuCl3 → AuCl + Cl2 (>160 °C)
3 AuCl → AuCl3 + 2 Au (>420 °C)
|
Anyone see the problem? My guess is, in an atmosphere of chlorine, the reaction equilibrium stays on the left even past the temperature where it
normally decomposes ?: AuCl3 → AuCl + Cl2 |
Oh, I see it. But I'm just sorta hoping for the best. All this gold(III) chloride stuff seems a little dicey. Like, it really irks me that
gold(III) chloride, tetrachloroauric acid, and chloroauric acid all seem to be used interchangably for both AuCl3 and HAuCl4,
which in some cases are claimed to be the same thing. I'd like to know where the other Cl comes from, myself.
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