Question

`K_(a)` for butyric acid is `2.0xx10^(-5)`. Calculate pH and hydroxyl ion concentration in `0.2M` aqueous solution of sodium butyate.

Answer 1

(I). Calculation of pH of the solution.
sodium butyrate is a salt of strong base and weak acid.
`pH =- 1/2 [log K_(w) +logK_(a) - logC]`
According to available data , `K_(w) =1.0 xx 10^(-14), K_(a) = 2.0 xx10^(-5) , C= 0.2 M`
`pH =- 1/2 [log 10^(-14) + log (2.0xx10^(-5))- log (0.2)]`
`=- 1/2 [(-14)- (5 -log2) +0.698] =-1/2 [-14-4 .699+0.698] =9.00`
(II). Calculation of hydroly ion concentration.
`pH =9 , pOH = pK_(w) -pH =14 -9 =5 :. [OH^(-)] =10^(-5) M`