Question

what happen if we mix distilled water in a reaction equilibrium of NaCl+CuSo4.?? which direction will it shift?? the answer needed according to Le Chantelier's Principle

Answer 1

in practice, NaCl should not change the pH of distilled water. There is no reason why it should. I think that the more complicated and important question is, what is the pH of the distilled water when you started? Also according to theory this should be pH = 7.00. But in practice this is not found to be true. If you take
conventional distilled water from a bottle in most laboratories, the pH will be found to be somewhat below 7.00. Possibly as low as 5.5 to 6.0. This is due to the dissolved CO2 in th e totally unbuffered water causing a drop in pH.
Now if your research tests showed that on addition of NaCl to "distilled water" that had an initial pH of say 6.0, the pH increased from the original 6.00 towards 7.00, then this is not a result of the NaCl increasing the pH of the water itself, but the salt is somehow reducing the acidifying effect of the CO2 in the water.

On the other hand, if you started with distilled water that definitely had a pH 7.00 and on addition of NaCl the pH rose towards pH = 8.00, then some serious thinking is necessary.

Some thoughts that come to mind are: what type of NaCl are you using? If comercial table salt, then anything is possible because additives are incorporated , such as CaCl2 , KI, etc to "improve" the salt. Who knows what impurities are present. Do you get the same results when you use an analytically pure laboratory reagent grade NaCl of guaranteed purity? It would be interesting to see your actual figures,
A final thought - My experience of pH meters - many years ago - was that they were not very reliable at neutral pH values.