Question

Acetic acid is a weak acid with a pKa of 4.76. What is the concentration of acetic acid in a buffer solution of 0.2M at pH 4.9. Give your answer in M but as a numeral only to 3 decimal places.

Answer 1

0.084 M

Step-by-step explanation:

Using the Henderson-Hasselbalch equation for a buffer ( a buffer is solution contain a weak acid and it conjugate base; the solution resist change in pH)

pH = pKa + log ( base/acid)

4.9 - 4.76 =log ( base / acid)

10^0.14 = ( base / acid)

1.38 = (base / acid)

since there is 0.2 M in the buffer solution

the concentration of acid =
`(1)/((1+1.38))` × 0.2 = 0.084 M