contestada

He pka values of a compound with two ionizable groups are pk1 = 4.10 and pk2 between 7 and 10. a biochemist has 10 ml of a 1.0 m solution of this compound at a ph of 8.00. she adds 10.0 ml of 1.00 m hcl, which changes the ph to 3.20. what is pk2?

Respuesta :

For the reaction of weak acid:

[tex] HA\rightleftharpoons H^{+}+A^{-} [/tex]

The Henderson-hasselbalch equation is:

[tex] pH = pk_a+ log \frac{[A^{-}]}{[HA]} [/tex]

The concentration ratio at [tex] pk_1 [/tex] is:

[tex] pH = pk_1+ log \frac{[A^{-}]}{[HA]}  [/tex]

Substituting the values:

[tex] 3.2 = 4.1 + log \frac{[A^{-}]}{[HA]}  [/tex]

[tex] log \frac{[A^{-}]}{[HA]}  = - 0.9  [/tex]

[tex] \frac{[A^{-}]}{[HA]}  = 0.126  [/tex]

Now, for calculating the pk_2 value:

[tex] pH = pk_2+ log \frac{[A^{-}]}{[HA]}  [/tex]

[tex] 8 = pk_2+ log(0.126)  [/tex]

[tex] pk_2 = 8.9 [/tex]

Thus, [tex] pk_2 = 8.9 [/tex].



Otras preguntas