# Activity of NaCl aqueous solution at high ionic strengths: Common-ion effect

Is there any theoretical way to estimate the activity of $$\ce{NaCl}$$ at high ionic strengths in water and that in $$\pu{7 M}$$ $$\ce{NaCl}$$ solution? This question is based on whether solubility of $$\ce{NaCl}$$ in $$\pu{7 M}$$ $$\ce{LiCl}$$ solution should decrease. Solubility of $$\ce{Na+}$$ in $$\ce{LiCl}$$ solution can be approximated to

$$[\ce{Na+}]=\frac{(K_\mathrm{sp})_{\ce{NaCl}}}{m_{\ce{LiCl}}}$$

We have, however, assumed that both $$\ce{NaCl}$$ (and $$\ce{LiCl}$$) are in their unit activities, which is not true. How to get conservative estimates for $$a_{\ce{LiCl}}$$ and $$a_{\ce{NaCl}}$$ at high ionic strengths, say $$\pu{7 M}$$?

• Mathematical modeling has progressed greatly since I was a student, but I believe that such activities would rely on experimental measurements rather than theory. – MaxW Sep 19 at 23:43