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For calculation of the osmotic pressure, we can use Van't Hoff equation as below:

π=CRT

If we put the solution in an electrical field, the cations and anions move towards negative and positive pols, respectively. To calculate the osmotic pressure near the poles in which the ions are not neutral (for example we have 3 times more Na+ than Cl- near the negative pole), Should we calculate the osmotic pressure by summing the molarity (C in Van't Hoff equation) of each ion and use the Van't Hoff equation?

π=(CNa++Ccl-)RT

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  • $\begingroup$ 3x more cations than anions or vice versa would cause the discharge blowing solution from the vessel and possibly yourself from a room. $\endgroup$
    – Poutnik
    Commented Sep 14, 2022 at 18:42
  • $\begingroup$ But, electrodialysis is working on this basis; the anions couldn't pass through CEMs and vice versa. It causes accumulation of ions near the membrane if they couldn't pass through it (for example accumulating of anions on the surface of CEM). $\endgroup$
    – MENG
    Commented Sep 14, 2022 at 19:38
  • $\begingroup$ Could it be 1.5 times higher? $\endgroup$
    – MENG
    Commented Sep 14, 2022 at 19:42
  • $\begingroup$ A very slight charge disbalance creates a strong potential gradient acting against external potential gradient.You can calculate it, using estimated solution permitivity. $\endgroup$
    – Poutnik
    Commented Sep 15, 2022 at 1:57
  • $\begingroup$ Another thing is, if the excess is being eliminated by electrode reactions during electrolysis, with providing or withdrawing of electrons. $\endgroup$
    – Poutnik
    Commented Sep 15, 2022 at 2:06

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