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Author: Subject: Identification of a mystery metal
MrHomeScientist
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[*] posted on 6-5-2019 at 11:32


So you measured the weight with an analytical balance; good! That should be pretty accurate (assuming it's calibrated; it couldn't hurt to double check that against calibration weights).

Now, how was the volume measured?

I know it seems like we are harassing you about the density, but you have 3 very different measurements there and we are trying to find where the discrepancy is. If your density measurements and calculations are accurate, then these rods might not all be the same alloy. It's an interesting problem, and we just want to be thorough.
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Sulaiman
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[*] posted on 6-5-2019 at 16:04


Using the method that I pointed to it does not matter if the scales are neither accurate nor calibrated ,
- it only relies upon zero and the linearity of the scales, and care of the operator.
(and that the sample does not react with air or water)




CAUTION : Hobby Chemist, not Professional or even Amateur
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MrHomeScientist
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[*] posted on 7-5-2019 at 08:20


Yep, I definitely recommend the specific gravity method. It's worked perfectly for me, and only requires one instrument so you avoid a lot of potential measurement error.
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stamasd
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[*] posted on 7-5-2019 at 15:39


The most accurate method to quickly determine the composition of a metal piece is by spectroscopy. Spark or plasma spectroscopy more precisely.
Essentially, a spark or arc is created by passing electricity between an electrode of a known composition (graphite usually) and the metal to be analyzed. The light emitted by the arc is passed through a prism, and the spectrum is photographed. Each metal produces a very characteristic pattern of emission lines, and based on the position of the emission lines in the spectrum you can determine which metals are present. Also the relative intensity of the lines belonging to each metal gives you an estimate of the relative proportions.
If your teacher wants to go this route, the chemical mystery could turn into a nice combined physics+chemistry experiment.
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Ozone
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[*] posted on 7-5-2019 at 16:03


I have a can of Cadmium metal sticks that look a lot like these (likewise, the can). However, the absence of yellow CdS which is evident (sparse patches) makes this less likely. The density of Cd is about 8.65 g/cc, which seems pretty close.

Cheers,

O3




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opfromthestart
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[*] posted on 11-6-2019 at 13:04


More on tests:
It reacts very quickly with nitric acid to form a white precipitate, which seems poorly soluble.
It reacts very slowly with hydrochloric acid, slowly bubbling after a few minutes.
It probably does not contain any lead or silver as no precipitate formed when sodium chloride was added to a solution of the precipitate from the nitric acid reaction.




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fusso
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[*] posted on 11-6-2019 at 22:48


"solution of the precipitate"? if it's insoluble how did you dissolve it?
One of the metal which form a white ppt when reacted with HNO3 is Sn.




Useful sites:
Balance Chemical Equation: http://www.webqc.org/balance.php
Molecular mass and elemental composition calculator: https://www.webqc.org/mmcalc.php
Solubility table: https://en.wikipedia.org/wiki/Solubility_table
Azeotrope table: https://en.wikipedia.org/wiki/Azeotrope_tablesIt's not crime if noone finds out - Nyaruko
List of materials made by ScienceMadness users: https://docs.google.com/spreadsheets/d/1nmJ8uq-h4IkXPxD5svnT...
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Cryolite.
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[*] posted on 11-6-2019 at 23:31


I'm thinking the mystery metal is tin as well. To test for tin, dissolve shavings of the metal in hydrochloric acid and add zinc granules. After the zinc has fully reacted, dip a water-filled test tube into the mixture and then hold it in the flame of a bunsen burner. An electric blue glow on the test tube indicates the presence of Sn ions.

Here's a video demonstration of this test: https://www.youtube.com/watch?v=rY9LcPj_eU8
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AJKOER
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[*] posted on 18-6-2019 at 16:18


A test that may be of value, especially if it is an alloy, is place a small piece of the unknown metal in a microwave safe vessel with vinegar, may be some 3 % H2O2 and a must, a little NaCl. Now take a small piece of stainless steel (as one possible choice, or copper, or zinc, or....) as the second electrode. Ideally, try to keep the approximate electrode surface area about the same (you can use multiple pieces of the stainless steel, if needed, to achieve this).

Microwave for 2 minutes and determine which electrode is being attacked. If it is unclear, think of swapping out the vinegar for another acid.

The metal/alloy that is less noble will NOT be attacked. Lookup the anodic index of various alloys and choose another until you witness an alternation between experiments of the metal moving from noble to more anodic (or the other way around). This may can you an idea of the anodic index of the possible alloys/metals consistent with its electrochemical behavior.

You can also freeze the product solution after the test and try to recover any crystals for added clues using the crystals color, shape and size if it was subject to anodic corrosion.

[Edited on 19-6-2019 by AJKOER]
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