<u>Answer:</u> The concentration of acetic acid and sodium acetate (acetate ion) is 0.06 M and 0.34 M respectively
<u>Explanation:</u>
We are given:
Concentration of buffer solution having acetic acid and sodium acetate = 0.4 M
Let the concentration of acetic acid be x M
So, the concentration of sodium acetate will be = (0.4 - x) M
To calculate the concentration of acid for given pH, we use the equation given by Henderson Hasselbalch:
![pH=pK_a+\log(\frac{[salt]}{[acid]})](https://tex.z-dn.net/?f=pH%3DpK_a%2B%5Clog%28%5Cfrac%7B%5Bsalt%5D%7D%7B%5Bacid%5D%7D%29)
![pH=pK_a+\log(\frac{[CH_3COONa]}{[CH_3COOH]})](https://tex.z-dn.net/?f=pH%3DpK_a%2B%5Clog%28%5Cfrac%7B%5BCH_3COONa%5D%7D%7B%5BCH_3COOH%5D%7D%29)
where,
= negative logarithm of acid dissociation constant of acetic acid = 4.76
![[CH_3COONa]=0.4-x](https://tex.z-dn.net/?f=%5BCH_3COONa%5D%3D0.4-x)
![[CH_3COOH]=x](https://tex.z-dn.net/?f=%5BCH_3COOH%5D%3Dx)
pH = 5.5
Putting values in above equation, we get:

So, concentration of acetic acid = x = 0.06 M
Concentration of sodium acetate = (0.4 - x) = (0.4 - 0.06) = 0.34 M
Hence, the concentration of acetic acid and sodium acetate (acetate ion) is 0.06 M and 0.34 M respectively