Question

A buffer contains equal molar concentrations of a weak acid (pKa=4.76) and the salt of the weak acid and a strong base (Mol Wt= 112.5). The buffer capacity of this solution is 0.33. Calculate the grams/L if the salt in this solution.

Answer 1

PH = Pka + log ([A^-] / [HA])
but in question it is given that [A^-] = [HA] so PH = Pka
let us say x moles of base is introduced into buffer and assume there 1 mole of both acid and its salt
mol of base added is not given in the question.
[A^-] = 0.5+x ; [HA] = 0.5-x ; substitute them in the Henderson Hasselbalch equation
to get new PH.
Now find ΔPH = new PH - 4.76
Buffer capacity,β = 0.33
β = ΔB / ΔPH
substitute the values in the above equation to get ΔB which is in gm/L