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Hi there, I am reviewing equilibrium. About this question, I wonder if the chemical equation is wrong. Because the description says 'a solution of mercury(I) nitrate is formed'. However, in the equation, the product is Hg2 2+? I thought the product should be Hg1+. Here is my answer, but my answer seems to be wrong.

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    – Poutnik
    Commented Nov 15, 2023 at 8:43

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Your expression would be correct if the mercury(I) ions were individual, separate atoms like most metals. But they are actually paired up, forming $\ce{Hg_2^{2+}}$ with a covalent bond between the metal atoms. Thus, properly,

$\ce{Hg(l) + Hg^{2+} <=> Hg2^{2+}}$

with $K_c$ then equalling $\ce{[Hg2^{2+}]/[Hg^{2+}]}$ as given in the textbook.

This behavior of forming diatomic metal(I) ions is actually known with several elements in Group 2 and Group 12 (or if you are using an older text, Group 2A and Group 2B), but mercury is the one that most commonly has metal(I) ions and not always metal(II). So your textbook (presumably) identifies specifically mercury as forming $\ce{Hg2^{2+}}$.

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