How to solve this problem on pH and buffer solutions....?

Question

To a buffer system containing 0.1M acetic acid and sodium acetate each, 0.01M of sodium hydroxide is added. The pH of the system is 4.76.Calculate the change in concentration of the salt due to the addition of alkali.

Answer 1

acid --> H+ & anion  , the NaOH removes the H+, & the reaction shift to the left increasing the concentration of the anion by "x",  & decreasing the concentration of the acid by "x"

the K for acetic acid is 1.8e-5, its pK = 4.74

the henderson Hasselbach equation says:

http://en.wikipedia.org/wiki/Henderson_H...

PH = Pka & log [anion] / [acid]

4.76  = 4.74  & log [anion] / [acid]

0.02  =  log [anion] / [acid]

10^x for both sides

1.047  =   [anion] / [acid]

1.047  =   [0.1+x] / [0.1-x]

1.047 [0.1-x] =   [0.1+x]

0.1047  - 1.047x =   0.1+x

0.1047  - 0.1  = 1.047x  +  x

0.0047 = 2.047x

x = 0.002296 molar change in concentration

your answer is: 0.002 Molar change