Question

Complete and balanceNaCl(aq)+Hg2(C2H3O2)2(aq)

My answer 2NaCl(aq) +Hg2(C2H3O2)2(aq) --2HgCl(s) + 2NaC2H3O2 (aq) is wrong and I don't understand why. They said "Check the grouping of your atoms and the solubility of your products. Mercury exists as the diatomic cation Hg2+2." Can you explain what I am doing wrong?

Answer 1

Mercury (I) is a dimer consisting of a mercury (II) ion and a neutral mercury atom. There are no individual mercury (I) ions. This is why there is no HgCl, only Hg₂Cl₂. It is said that mercury (I) (Hg₂²⁺) disproportionates to form mercury (II) and mercury metal as if this were a redox reaction and the mercury was changing oxidation state. But instead of a redox reaction to make Hg and Hg(II) from Hg₂²⁺, it simply decomposes. There is no electron transfer because the Hg₂²⁺ ion exists as an atom of mercury bonded to a Hg²⁺ ion, as in Hg-Hg²⁺.

Hence the balanced chemical reaction is

2NaCl (aq) +Hg₂(C₂H₃O₂)₂(aq) Hg₂Cl₂(s) + 2NaC₂H₃O₂ (aq)