# Question 9732f

May 20, 2017

You can't do it.

#### Explanation:

To make a buffer with pH = 9, you need an acid with "p"K_text(a) = 9 ± 1#.

Citric acid is a tribasic acid with the formula ${\text{C"_6"H"_8"O}}_{7}$ or ${\text{H"_3"C"_6"H"_5"O}}_{7}$.

The weakest form of the acid, $\text{HC"_6"H"_5"O"_7^"2-}$ has a $\text{p} {K}_{\textrm{a}}$ of only 6.40.

Thus, you can't use it to make a buffer with pH = 9.

However, it would be great for making a buffer with pH = 7.