Question

A 0.1 M solution of weak acid HA is 1% dissociated at 25°C. What is its K_a? If this solution is with respect to NaA 0.2 M, what will be the new degree of dissociation of HA and pH? 

Answer 1

Now 0.2 M NaA, a salt of HA,is added to it resulting a buffer solution of [HA] = 0.1 M and [NaA] = 0. 2 M

∵ [A^– ] is provided by NaA since dissociation of HA in presence of NaA is suppressed due to a common ion effect.