In aqueous solutions at 25° C, the product of the H + and OH - concentrations is
always 10 - 14, as expressed in this equation:

[H +] [OH - ] = 10 - 14

This allows calculation of the OH - concentration if the H + concentration is
known.

[OH - ] = 10 - 14 / [H +]

[OH - ] = 10 - 14 / 10 - 3 = 10 - 11

This calculation is used when the solution in question is not pure water, but
contains some mixture of acids and bases.

-----------------------

CH3COO (acetic acid) CH3COO- (acetate ion) + H+ ; pKa = 4.8;

-------------------------------------

pKa and pH
The "operational" relationship between pKa and pH is mathematically
represented by Henderson-Hasselbach equation:

pH = pKa + log [A-] / [HA]

-----------------------------------

ala-gly-ser-gln-lys-trp-arg-pro-gln-his

-----------------------

Bicarbonate, HCO3-, is in equilibrium with CO2 and H2CO3 (carbonic acid) as
follows:

CO2 + H2O [H2CO3] H+ HCO3-
blood