Question

Normally, the pH of the human body is fixed in a very narrow range between 7.35 and 7.45. A patient with an acidotic blood pH of 7.3 may be treated with an alkali such as sodium hydrogen carbonate. Why would this treatment raise the pH of the blood?

Answer 1

As equation below the diagram says Carbonic ion is the conjugate base i.e, HCO3- .

    and it come from , ​NaHCO3 ---> Na+ + HCO3-

and the pH is less than the normal pH of the buffer i.e, 7.3 < 7.35 that means less of H2CO3 than HCO3- ( since, less pH means acidic nature i.e, acid content is more so we have to increase base content i.e., H2CO3

so, From Lechatlier's principle, for below reaction, Equillibrium shitfs from right to left ,

                                           H2CO3 + H2O <=====> HCO3- + H3O+

That means concentration of H3O+ will decrease and concentration of H2CO3 will increase. Where the H2CO3 is basic nature compound. i.e., basic nature increases ==> pH increases.

                     Or

From the, Hinderson-Hasselbalch equation,

pH = pKa + log ( [ conjugate base] / [weak acid] )

from the above equation, if we increase the conjugate base i.e, H2CO3 then value of   log ( [ conjugate base] / [weak acid] )

will increase. ===> pH will increase.