The buffer capacity of a buffer solution consisting of a weak acid, HA and its salt, NaA becomes maximum when its pH is 5.0. at this pH, what is the relation between the molar concentration of HA and NaA? Also find the value of `pK_(a)` of HA.

Explanation

In case of a buffer solution consisting of a weak acid and its salt, the buffer capacity of the solution is maximum when `pH=pK_(a)`. It is given that buffer capacity of the given buffer is maximum when its pH=5. therefore, `pK_(a)` of the weak acid present in the buffer is 5. Now, pH of a buffer solutionn consisting of a weak acid and its salt is given by `pH=pK_(a)+"log"(["salt"])/(["acid"])`
Since, `pH=pK_(a)=5,"log"(["salt"])/(["acid"])=0 or, `["salt"]=["acid"]`
`therefore [NaA]=[HA]`.