metalresearcher
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Which alloy (Au / Cu?) is this ?
I have a gold colored chain (color is similar to 18karat gold) and thought that it is not gold.
So, I tried to immerse it in a 10% HNO3 solution (already used for cleaning sterling silver so it has a slightly bluish tinge of Cu2 +). Cold: no
reaction, hot: vigorous gas evolution. My conclusion: it's brass or other copper alloy. I also dipped a real 18 (even chain) and 14 k (ring) gold
piece into the hot solution: nothing happens.
But the solution is a bit greenish i.e. that the alloy does have anything other than Cu. And the surface of the metal remains yellow on the part which
is immersed in the solution.If it is brass or bronze, then it ihas a pink color: Zn or Sn is easier dissolved than Cu.
And something other strange issue: The contents of the chain is 2.2cm3 and it weighs 22 grams (10 g/cm3), so it must contain an unknown heavy metal
heavier than Cu. It contains Ag because after dipping in the HNO3 solution I dipped it into the water the water gets a milky appearance (AgCl). But
there is not so much Ag in it as the metal is too yellow.
Does anyone know what can it be?
[Edited on 2012-8-25 by metalresearcher]
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weiming1998
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Quote: Originally posted by metalresearcher  | I have a gold colored chain (color is similar to 18karat gold) and thought that it is not gold.
So, I tried to immerse it in a 10% HNO3 solution (already used for cleaning sterling silver so it has a slightly bluish tinge of Cu2 +). Cold: no
reaction, hot: vigorous gas evolution. My conclusion: it's brass or other copper alloy. I also dipped a real 18 (even chain) and 14 k (ring) gold
piece into the hot solution: nothing happens.
But the solution is a bit greenish i.e. that the alloy does have anything other than Cu. And the surface of the metal remains yellow on the part which
is immersed in the solution.If it is brass or bronze, then it ihas a pink color: Zn or Sn is easier dissolved than Cu.
And something other strange issue: The contents of the chain is 2.2cm3 and it weighs 22 grams (10 g/cm3), so it must contain an unknown heavy metal
heavier than Cu. It contains Ag because after dipping in the HNO3 solution I dipped it into the water the water gets a milky appearance (AgCl). But
there is not so much Ag in it as the metal is too yellow.
Does anyone know what can it be?
[Edited on 2012-8-25 by metalresearcher] |
Test it.
1, Add concentrated NaCl(aq) to the dissolved chain solution. filter/decant out precipitate, that is the silver content. You can further verify that
it is Ag and not Pb by exposing the precipitate to light.
2, Add excess NaOH(aq) to solution and filter. The filtrate could contain aluminum, zinc, tin, etc. Add just enough HCl until all precipitate
dissolves, then boil solution. Any tin (II) chloride will slowly hydrolyse and form a precipitate. This is your tin content.
3, Add Na2CO3, then dissolve precipitate in dilute acid. Zinc oxide dissolves easily.
4, To the residue that you filtered out, dissolve it in H2SO4 and add citric acid, sodium carbonate and glucose. Copper precipitates out as Cu (I)
oxide while any nickel is either still complexed in the solution, or already precipitated out when you added the sodium carbonate.
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blogfast25
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MR:
How did you determine density? Volume of the chain can be determined by suspending it in a tared container filled with water: the scale reading is the
buoyancy in g and thus in cm3. Getting density reading slightly wrong is easy to do.
10 % HNO3 really is a bit of a slow boat to China. Try and get some 'pH Down' from the Pot People: that's 35 %, good enough. It will dissolve just
about anything that's in there, bar gold and even nobler metals (Pt, Ir, Rh, ...)
Weiming: as long as there some acid reserve, SnCl2 won't hydrolyse until a high concentration of it obtained. I've boiled in acidified SnCl2 several
times. It's possible to crystallise it from acid solution. That's how the dihydrate is produced.
[Edited on 25-8-2012 by blogfast25]
[Edited on 25-8-2012 by blogfast25]
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AJKOER
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| Quote: Originally posted by metalresearcher | ..........
And something other strange issue: The contents of the chain is 2.2cm3 and it weighs 22 grams (10 g/cm3), so it must contain an unknown heavy metal
heavier than Cu. It contains Ag because after dipping in the HNO3 solution I dipped it into the water the water gets a milky appearance (AgCl). But
there is not so much Ag in it as the metal is too yellow.
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My limited experience with Silver chemistry is how often I make yellow Silver carbonate without trying!
Use freshly boiled distilled water to remove one possible CO2 source, as well as limiting atmospheric contact.
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LanthanumK
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@metalresearcher; you only need a tiny amount of dissolved silver to make a cloudy solution of silver chloride. A significant change in the color of
the alloy would only happen with a much larger % of Ag, AFAIK.
hibernating...
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