hi! i've been testing different metals with nitric acid during "training" classes, and we were told that some 18kt WG may actually be stainless steel. i'll have to tell y'all about the training classes, very interesting....
hi, i learned that 22kt nitric acid solution will turn some stainless steel jewelry black after testing. and, of course, platinum will not react with nitric acid solution, and doesn't react with most acids, but, will react with aqua regia.
Had an antique jeweler show me a neat trick to tell white gold from plat: do a streak on your acid plate, white gold is always yellowish and platinum is very white (use your microscope or loop), sometimes a platinum sample ring (from the wedding band case) will help. Also, I took a piece that was supposed to be platinum to our jeweler and he put his torch to it, said steel will turn black but plat is not affected. Also, also...by running a jeweler's file over the metal (very lightly) you will learn to feel the gumminess of plat whereas other metals will let the file slide by. A microscope and probe will also help differentiate on an insconspicuous spot; plat is very soft, others metals not so.
Joined: Fri Jun 25, 2010 10:06 pm Posts: 1478 Location: Rochester, MN / Toronto, ON
I'm not sure if this would work as a test for platinum, since I'm not sure if other metals can do this. Please DON'T try the second part unless you can work it out and make sure the chemistry is valid.
Platinum's a catalyst for lots of reactions, mainly anything with hydrogen gas. You can stick platinum jewelery in hydrogen peroxide, and it'll bubble and fizz without damaging the platinum. As far as I remember from chem, if you expose platinum to hydrogen gas in the presence of oxygen, you can get flames (combine aluminum foil with HCl to get your hydrogen?).
Hi Too-shiny, I tried the hydrogen peroxide on a platinum ring at home with no reaction. I just used drug store strength liquid. Does irridium in the alloy inhibit the reaction, or do I need stronger solution? Have you had personal success with this test? Thanks, Richard.
Joined: Wed Feb 25, 2009 5:53 pm Posts: 153 Location: Toronto
There are quite a few problems with it Richard. Yes, he is right that many hydrogenations/reductions are catalyzed by platinum and palladium, due to the interaction of one atom from the homonuclear diatomic (ie - one of the Hs in H2) with the exposed surface of the catalyst (to be more specific).
I'll discuss them below, but the important points are: *Plat AND Palladium both catalyze the same kind of reduction rxns via hydrogen's interaction with it when H is bound to something w/ low difference in electronegativity.
*H2O2 decomp doesn't produce H2 gas, it catalyzes the decomp to H2O and O2
*Solid-state Catalysis is dependant on surface area... Chemists use Pt Black (finely 'powdered' Plat), where 1 gram has surface area of 20-25 m^2. That is likely larger than the biggest piece of Plat jewelry ever created.
*Peroxide concentration would likely have to be 30% percent, to have ANY chance of observing bubbling from O2 liberated (hydroponics stores sell it at that conc) ------------------------------------- Now the catalytic effect of platinum/palladium on peroxide does not liberate H2 gas at all... but O2. It actually catalyzes an isomerism (ie - re-arrangement), that produces an unstable species/molecule, that then reacts with another re-arranged molecule to produce the H2O and O2... this happens so quick it's hard to detect without IR spec. Unfortunately many things perform this catalysis, such as Mg (but I'm assuming Steel vs Pt is the reason for this) -- So no H2 to burn is problem 1. But, if an effective catalyst... you might see bubbling you say? Two problems:
With plat as a catalyst, chemists don't use platinum in the form of a ring or chunk of metal. A solid state catalyst's effect is proportional to the surface area exposed to reagents. Thats why the use "platinum black" (and palladium black, as palladium act very similarly). Pt-black is platinum that is made up of such TINY TINY grains that it actually appears to the eye as a black powder. Even the biggest piece of plat jewlery in existence doesn't have a comparable surface area (20-25m^2/gram).
Problem two is that... yes, the peroxide concentration would be far too low to have a noticable effect on bubbling. To have ANY chance with jewelry-like surface areas of platinum (which I'm skeptical of), you would definitely need concentrations that are used in the production of the strong per-***** acids/anions (peracetate, persulfate, etc). If you wanna keep trying (because something that depends on the catalytic effect would narrow down to Plat and Pallad), try a hydroponics store for 30%, and if you can't find one... I'll PM you other places that will sell it without licensing/credentials.
Separating Plat+Pallad is easy... and if we could 'fake'/use something else for the Pt/Pl hydrogenation catalysis, you wouldn't have any in your car (or in the chem lab), Pt/Pl would not be worth as much as they are now (even with the rarity)
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