bocaJ
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Black Substance Formed by Reacting Aluminum with NaOH
I was trying to make sodium aluminate by reacting aluminum foil with a 5M solution of NaOH. The reaction produced a lot of heat and gas as expected,
but a black tar-like substance formed instead of a clear-to-cloudy solution that I was expecting. I thought that there might just be some sort of
impurity in the foil, so I repeated the procedure with aluminum lathe turnings from a machine shop, only to observe the same black substance after the
reaction subsided. A few days earlier, I tried creating hydrated aluminum chloride by reacting aluminum foil with HCl(aq). That also produced a black
substance. When I heated the black substance from the NaOH reaction, a white solid formed. What exactly is this black substance? And how do I prevent
it from forming in reactions with aluminum metal?
TL;DR: A black tar-like substance formed by reacting aluminum with NaOH(aq), and by reacting aluminum with HCl(aq). What is it?
Also, I'm new, so I'm sorry if this thread is in the wrong place.
[Edited on 6/14/2018 by bocaJ]
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fusso
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https://www.sciencemadness.org/whisper/viewthread.php?tid=80...
It's probably silicon impurities.
[Edited on 14/06/18 by fusso]
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bocaJ
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Thanks! I had to filter the solution several times before I could get a clear one. I did some research and found that pure aluminum is almost never
used in industry. IIRC the lathe turnings were 6061 alloy, which contains Mg, Si, Fe, Cu, Zn, Ti, Mn, and Cr. I'm not sure what alloy the foil is.
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alking
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Yeah, aluminium foil is very pure, but it has all kinds of minor impurities. That's likely going to be the case for most industrial metals. It's not
too difficult to get to 99%+ purity, but removing those last traces takes an exponential amount of work that just isn't worth it in most cases; that's
probably true of most things really, metal, organic, or what have you. It depends how it's made of course and will vary.
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