[xshadow]

For a buffer solution:
HA and Na+A-

How can i calculate the protonic balance quickly in order to calculate pH??

I have to do the protonic balance of HA and NaA and than adds them?

B.P HA+H₂O   --->  [A^-] + [OH^-]= [H⁺]
B.P A^-+H₂O  ---> [OH^-]= [H⁺] + [HA]

To get the PB of the Buffet solution I have to add the two protonic balance  that I have found'??
Thanks

[AWK]

Just write down K_a for Bronsted acid present in a buffer solution (molecular acid or ionic one eg [NH₄⁺]), then rearrange equation for [H₃O⁺]. And you will obtain equation that in logarithmic form is known as Henderson-Hasselbach equation that works for most buffer solutions.
Note - using K_a for Bronsted acid present in buffer solution you need only one equation for practically all "student" buffers.

http://www.chembuddy.com/?left=pH-calculation&right=pH-buffers-henderson-hasselbalch

[xshadow]

Just write down K_a for Bronsted acid present in a buffer solution (molecular acid or ionic one eg [NH₄⁺]), then rearrange equation for [H₃O⁺]. And you will obtain equation that in logarithmic form is known as Henderson-Hasselbach equation that works for most buffer solutions.
Note - using K_a for Bronsted acid present in buffer solution you need only one equation for practically all "student" buffers.

http://www.chembuddy.com/?left=pH-calculation&right=pH-buffers-henderson-hasselbalch

thanks AWK