# Are all salts completely dissociated in solution when put in smaller amounts than their molar solubility?

From what I understand, the solubility is given in terms of molar solubility (or $$\pu{K_{sp}}$$), from which it can be easily calculated). Indeed, the saturation point represents the maximum amount of a slightly soluble substance in an aqueous solution that solubilizes (dissociates). Therefore, in extremely small amounts even very sparingly soluble salts with extremely small molar solubilities (and $$\pu{K_{sp}'}$$) can be completely ionized. For instance, $$\ce{HgS}$$ is one of the least soluble inorganic substances with a molar solubility of about $$\ce{10^{-27}}$$. Now, if I put up to $$\ce{10^{-27}}$$ moles of HgS in 1L of water, will it be completely dissolved into $$\ce{Hg^{2+}}$$ and $$\ce{S^{2-}}$$?

• HgCl2 is reportedly in large extent covalent. Some salts forms ionic pairs, like MgSO4 in sea water. Other may form charged or neutral complexes. Jul 29 at 5:18
• This is an equilibrium process and so to calculate the extent of reaction you can use the usual methods starting with different initial amounts. Jul 29 at 7:16
• A solubility of $\ce{10^{-27}}$ M corresponds to $1$ atom $\ce{Hg}$ and $1$ atom $\ce{S}$ in $10^4$ liters, or in $10$ metric tons. This is practically zero atom per litre. This amount is not detectable. Jul 29 at 8:22
• You cannot put less than $\pu{\frac{1}{N_\mathrm{A}} mol}$ of anything anywhere, as it would be less than 1 object. Jul 29 at 10:31
• Yes. Ksp describes a saturated solution. If from dissolution of a salt stoichiometric quantities of cation & anion will be dissolved ("in solution') Jul 29 at 12:28