How to solve...

Buffers withstand the change of the $pH.$ The buffer of the highest buffer capacity is when the concentration of the weak acid $(HA)$ and its conjugate base $(A^{-})$are close to each other. In the problem below $0\mathrm{.}1M$ acetate buffer means that $[HA]+[A^{-}]=0\mathrm{.}1M.$ Answer the following question. Show the solution or explain how you are going to solve it:

Calculate the concentration of acetic acid and acetate ion in a $0\mathrm{.}1M$ acetate buffer at $pH5.$ The $p{K}_a$ of acetic acid is $4\mathrm{.}76.$