[Borek]

Good result, but assuming the ionic force comes from eg KNO3, but not NaCl+HCl (this aproximation is, of course, quite sufficient to solve student problems)

Can you elaborate, I m not sure I understand what you mean. In the calculations total ionic strength of the solution was forced to be 0.01 - it doesn't matter whether it is done adding NaCl, KNO₃ or any other salt that can be considered inert.

[AWK]

I mean SIT theory (specific interaction theory) which gives slightly different activity coefficients depending on electrolyte used