# Why can’t I use solubility product for normally soluble compounds?

Solubility product only applies to sparing soluble ionic compounds (chemguide)

I read this in a website. But I don’t see what this should be the case. Taking $$\ce{NaCl}$$ for example, there’s an equilibrium established as it dissolves. Why then does solubility product not apply to this scenario?

• You could calculate it, but it's wouldn't be all that useful. – Mithoron Jul 1 at 14:49
• At high ion concentration, solubility products are activity driven and there are not good models for activity coefficients of such solutions. Using ion concentrations, the effective solubility product would be widely solution composition dependent. – Poutnik Jul 1 at 16:37