I was thinking in a case where the solute and solvent are two different polar liquids and according to Does the acidity constant depend on the solvent? the constant of dissociation change with the solvent, but changing the amount of liquid of the solute and solvents change their roles so my question is: Do the two liquids influence each other and their constants of dissociations of both liquids change at the same time while you change the amount of liquids?

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    $\begingroup$ No, constants don't change, that's why we call them constants. Say, if you were to mix H2SO4 and HClO4, there will be some dissociation constants of both acids (different from those in water), and they won't depend on the relative amounts. $\endgroup$ Mar 8, 2023 at 21:36
  • $\begingroup$ @IvanNeretin thanks for replying, so even if the constants of dissociation don't change, their activities change. $\endgroup$ Mar 8, 2023 at 21:41
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    $\begingroup$ They do, and so does the degree of dissociation, but not the constants. $\endgroup$ Mar 8, 2023 at 21:46
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    $\begingroup$ True TD constants would depend on temperature only, using activities of both conjugate pairs $\ce{HA + B <=> A- + BH+}$. These activities may change a lot in different mixtures. But the point is, most dissociation constants are not true TD constants, but they implicitly involve simplifying assumptions with limited scope of applicability. $\endgroup$
    – Poutnik
    Mar 9, 2023 at 9:29
  • $\begingroup$ @IvanNeretin As you increase the fraction of solute beyond 50%, the role of solvent and solute (and with it the definition of the standard state) changes, so you would expect the constants to change as well (just like when you switch to a different physical state). $\endgroup$
    – Karsten
    Mar 10, 2023 at 23:30


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