[medastar]

Hi mates,

Can any one help me in my issue or give an explanation, I need to fix the pH of NaCl solution of 2% NaCl concentration in distilled water. I am trying to add drops of alkali (NaOH) to the solution to make pH reach 8. then after reaching 8 pH starts to decrease again gradually with time (it decreased to 7 pH in 6 mins).
I need any help or any illustration of that incident, knowing that the distilled water is pure and the NaCL powder is was perfect condition and i tried two pH meters in excellent conditions and new in technology, i tried with different NaCl solutions but the same issue happens every time.   

Kind Regards

[Borek]

First suspect: atmospheric CO₂.

In general, if you need to keep pH constant, use a buffer.

[Irlanur]

Why do you need a "fixed" pH? you'll have a hard time without a buffer...

[medastar]

Thanks for your reply and advice, can you please tell me how to prepare that buffer?

[medastar]

Also how can Co2 in atmosphere affect this?

[Borek]

Thanks for your reply and advice, can you please tell me how to prepare that buffer?

http://www.chembuddy.com/?left=buffers&right=buffers

https://en.wikipedia.org/wiki/Buffer_solution

Also how can Co2 in atmosphere affect this?

What happens when CO₂ reacts with NaOH?