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?
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1$\begingroup$ Iron does form an amalgam with mercury: see for example this paper iopscience.iop.org/0953-8984/4/44/024. $\endgroup$ – J. LS Apr 18 '15 at 9:59
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$\begingroup$ Pt, W and Ta also resist dissolution with Hg en.wikipedia.org/wiki/Amalgam_(chemistry) $\endgroup$ – Mithoron Nov 11 '18 at 20:16
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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.
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3$\begingroup$ Mercury also forms an amalgam with aluminium, one of th reasons why it is banned on planes. $\endgroup$ – user15489 Apr 19 '15 at 3:41
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In Fe, Co, or Ni, the metallic bonds are very strong. Hence, they don't allow mercury to diffuse into it and as such, no amalgam is possible with these metals. In contrast, Ag, Au, or Na (i.e. soft metals) can readily adsorb mercury. Hence amalgam formation is possible with these metals.
Note: All metals mentioned above are of comparable size with Hg, i.e. they fulfil the amalgam formation condition.
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