A buffer is composed of equimolar weak and conjugate base...what is the #pH# of the buffer: #A.# #pH=pK_a# of #HA?# #B.# #pH=7?# #C.# #pH=([A^-])/([HA])?# #D.# #pH=([HA])/([A^-])?#

1 Answer
Aug 17, 2017

#"Option A"#

Explanation:

From this link #pH=pK_a+log_10{[[A^-]]/[[HA]]}#, which is a form of the buffer equation.

And thus in the scenario, #[A^-]-=[HA]# (#"Option A"# above), i.e. the concentrations of weak acid and its conjugate base ARE EQUAL, and are in appreciable concentration, and so..

#log_10{([A^-])/([HA])}=log_(10)1=0#, and thus #pH=pK_a#

Addition of base deprotonates #HA#; addition of acid protonates #A^-#. And thus the ability of the buffer to moderate gross changes in #pH# is maximized.