Question

The pka of hco3 - (or pka2 of h2co3) is 10.33. what is the ph of a solution that has 0.1 m na2co3 and 1.0 m nahco3?

Answer 1

The given solution is a mixture of $NaHCO_{3}$and $Na_{2}CO_{3}$. It acts as a buffer as it is a combination of the weak acid $HCO_{3}^{-}$and it's conjugate base $CO_{3}^{2-}$.

$[Acid] = [HCO_{3}^{-}]=1.0 M$

$[Base] =[CO_{3}^{2-}]=0.1 M$

pH of the buffer solution can be calculated from Hendersen-Hasselbalch equation as below:

$pH=pK_{a}+log\frac{[CO_{3}^{2-}]}{[HCO_{3}^{-}]}$

$pH=10.33+log\frac{0.1}{1.0}$

pH = 10.33+(-1)

     = 9.33