[o1ocups]

hello Borek here is my question again

"Second, while only solution with pH=7.00 is strictly neutral (see water ion product page for more information on neutral solutions pH), all solutions with pH in the range 4-10 have real concentration of H+ and OH- lower than 10-4M - which can be easily disturbed with small additions of acid and base (unless pH is kept constant by some buffer)."

What do you mean "real concentration" ? And why is it that if the H+ and OH- in a solution have concentrations lower than 10^-4 M they'll be easily disturbed? Is it true for all the solutions that has a pH between 4 and 10?

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And I still don't understand the relationship between the two water ion equations (1.7 and 1.4)...

Thanks.

[Borek]

Question is about content of this page:

http://www.chembuddy.com/?left=pH-calculation&right=water-ion-product

What do you mean "real concentration"?

Just concentration. "Real" is superficial.

And why is it that if the H+ and OH- in a solution have concentrations lower than 10^-4 M they'll be easily disturbed?

Because that means very small quantities of acids/bases added can be enough to shift pH by several units. 1 drop of 0.1M NaOH added to 10 mL of 10^-4 HCl changes pH from 4.00 to 10.60 (assuming - quite reasonably - that one drop has a volume of 0.05 mL).

Is it true for all the solutions that has a pH between 4 and 10?

No. It is explicitely written in the text you have quoted, that it doesn't work this way for solutions containing buffers.

And I still don't understand the relationship between the two water ion equations (1.7 and 1.4)...

Sorry, no idea how I can explain it better. Water concentration is assumed to be constant and 'moved' to Kw. Just an algebraical trick.

[AWK]

"Second, while only solution with pH=7.00 is strictly neutral

This is only an approximate statement - you should add temperature 298 K (25 C) to this statement,  since even pure and neutral water at different temperatures has different pH, eg. at 273 K (0 C) pH=7.47, and at 373 K (100 C) pH=6.14.

[Borek]

This is only an approximate statement - you should add temperature 298 K (25 C) to this statement

It is there, just the quote was not complete.

And it was not on the page I have linked to earlier, but here:

http://www.chembuddy.com/?left=pH-calculation&right=pH-scale