Can mercury dissolve in hydrochloric acid?

Answer 1

No. A metal will "dissolve" in acid if it ionizes (going from a neutral metal atom to a cation)... therefore this is an oxidation-reduction problem! Since Mercury goes from neutral to cation (positively charged ion), that means it loses electrons, or is oxidized. That means something else needs to be reduced (or gains electrons). In an HCl solution, you have lots of H+ and Cl-. Only H+ can gain electrons, since Cl- is already an anion (negatively charged ion). If you look at a table of standard reduction potentials, you see that

2H+ + 2e- => H2 E=0V

2Hg => Hg22+ + 2e- E=-0.80V

Therefore, the total reaction 2H+ + 2Hg => H2 + Hg22+ has a potential E=-0.80V, meaning this reaction is not spontaneous (since E<0V). In real life, adding mercury to HCl (no matter how concentrated) will just result in the mercury sinking to the bottom of the container.

Hope this helps.

Answer 2

Mercury is not soluble in hydrochloric acid, but it can form mercury chloride (HgCl2) when reacted with hydrochloric acid. This reaction produces hydrogen gas and can be accelerated by heating the mixture.