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I am learning about solutions and while giving an example of a liquid (solute) and a solid (solvent), my teacher told us that mercury forms an amalgam with all the metals except iron.

I want to know why this is so?

Gaurang Tandon
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Freddy
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    Iron does form an amalgam with mercury: see for example this paper http://iopscience.iop.org/0953-8984/4/44/024. – J. LS Apr 18 '15 at 09:59
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    Pt, W and Ta also resist dissolution with Hg https://en.wikipedia.org/wiki/Amalgam_(chemistry) – Mithoron Nov 11 '18 at 20:16

2 Answers2

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Iron does not form an amalgam readily, hence the use of iron electrodes in mercury switches. Apparently, iron does form alloys with mercury under specific conditions; see http://www.madsci.org/posts/archives/2011-04/1304143502.Ch.r.html.

By contrast, mercury spilled on gold (e.g. gold-alloy jewelry) soaks in immediately, discoloring the gold, and migrates further into the bulk metal in a few hours, thus restoring the color.

DrMoishe Pippik
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    Mercury also forms an amalgam with aluminium, one of th reasons why it is banned on planes. –  Apr 19 '15 at 03:41
  • As does gallium, both of which creep along the grain boundaries, destroying the integrity of the alumin(i)um in short order. https://www.youtube.com/watch?v=IgXNwLoS-Hw BTW, the (very toxic) mercury or (safer) gallium can be recovered by dissolving aluminum in the alloy in NaOH solution. – DrMoishe Pippik Sep 11 '22 at 00:53
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    The solubility of iron in mercury is less than 5x10^-7 wt%. This means a litre of mercury will dissolve less than 70 micrograms of iron (or 17 grams of gold), which is negligible. However, mercury still wets the metal and adheres to it, so iron and copper amalgams are possible by mixing mercury with a very fine metallic powder. Copper lays somewhere between gold and iron in solubility and it is still possible to make amalgam that hardens, though not with solid metal, only powder. – Libor Nov 14 '23 at 15:31
  • @Libor, that might also be expanded to an answer, with citations for the solubility. Thanks for the info. BTW, the solubility of iron seems to be quite temperature-dependent, decreasing above 87°C, in the answer. – DrMoishe Pippik Nov 14 '23 at 15:38
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In Fe,Co,Ni The Metallic Bonds Are Very Strong Hence Don't Allow Mercury To Diffuse Into It Hence No Amalgam With Them While In Other Metals Like Ag,Au,Na etc(Soft Metals) Mercury Can Easily Diffuse And Form Metallic Bonds With Them(Ag,Au,Na,etc) Hence Amalgam Formation In Them. Note:-All Metal Mentioned Above Are Of Comparable Size Of Hg i.e. Fulfilling Amalgam formation Condition.

Vishal Gupta
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