Which of the following expression tepresents the Henderson equation for an acidic buffer ?

Options

A. `pH=(1)/(2)pK_(a)-(1)/(2)logC`
B. `pH=pK_(a)-l"og"(["Conjugate base"])/(["Acid"])`
C. `pH=pK_(a)+"log"(["Conjugate base"])/(["Acid"])`
D. `pH=pK_(a)`

Answer

C

Explanation

`underset("acid")underset("Weak")(HA)hArr underset("base")underset("Conjugate")(H^(+)+A^(-))`
`K_(a)= ([H^(+)][A^(-)])/([HA])`
or, rearrangning terms,
`[H^(+)] = K_(a)([HA])/([A^(-)])`
Taking the negative logarithm of both sides of this equation gives
`- log[H^(+)]= -"log"(K_(a)([HA])/([A^(-)]))`
`= -log K_(a)+"log"([A^(-)])/([HA])`
or `pH= pK_(a)+"log" ([A^(-)])/([HA])`