# Does “covalent” AgCl (aq) exist and if so, how to quantify its concentration?

I am reading Ionic Equilibrium by James N. Butler. Using silver(I) chloride in excess aqueous chloride as an example it speaks of several forms: $\ce{AgCl (s)}$ i.e. the ionic crystalline salt, $\ce{Ag+(aq)}$ and $\ce{Cl^{-}(aq)}$ the aqueous ions from dissociation, and finally $\ce{AgCl(aq)}$, which Butler purports to be "dissolved covalent silver chloride molecules as distinct from solid salt or dissolved ions."

Does this "molecule" of $\ce{AgCl}$ really exist in solution? If so, is there a way to quantify the concentrations of this covalent species? Equilibrium solubility product constants seem to give the concentration of the aqueous ions only.

• For your second question: If you can determine the quantity of ions present in solution, you should easily determine the other quantity, i.e. the "covalent dissolved" AgCl. – CHM Sep 8 '12 at 1:57

Some amount of $[Ag Cl (H_2O)]$ particles should exist in solution from pure thermodynamic point of view. See, $Ag^+$ ion can coordinate two ligands, and in solution both $Cl$ and $H_2O$ are present. However, it should be really hard to detect trace amounts of this particle, as $AgCl$ is almost insoluble. In case one can get concentrated salt solutions, similar particles may exist and hints for their existence may be got from conductivity measurements and osmotic pressure. Sometimes a direct study using NMR is possible, which can give some structural information if used properly (see 2D-NMR methods). As I remember, $Cr(CH_3COO)_2$ hydrate is slightly soluble in water but undergoes little to no dissociation.