Question

What is the approximate buffering range of formic acid? a. You have a formic acid/potassium formate solution that has a pH of 4.75. What is the ratio of the formate to the formic acid? b.

Answer 1

Answer:

a. The buffering range is between 2.74 and 4.74.

b. The ratio of the formate to the formic acid is 10.23.

Explanation:

a. For every buffer solution, the optimal effective range is pH = pKa ± 1. Outside this range, the buffer does not work properly.

For the formic acid, the pKa is 3.74, thus the optimal range is between 2.74 and 4.74.

b. The Henderson-Hasselbalch equation is a chemical expression used to calculate the pH of a buffer knowing the ratio of the acid to base, or to calculate the ratio knowing the pH. The expression is:

$pH = pKa + Log \frac{[A^{-}]}{[HA]}$

where [A^{-}] is the concentration of the conjugate base and [HA] is the concentration of the acid.

For a formic acid/potassium formate solution that has a pH of 4.75 and pka of 3.74:

$pH - pKa =4.75 - 3.74 = 1.01 = Log \frac{[A^{-}]}{[HA]}$

$\frac{[A^{-}]}{[HA]} = 10^{1.01} = 10.23$