Question

You are given 10.00 mL of a solution of an unknown acid. The pH of this solution is exactly 4.08. You determine that the concentration of the unknown acid was 0.3250 M. You also determined that the acid was monoprotic (HA). What is the pKa of your unknown acid

Answer 1

Step-by-step explanation:

pH = 4.08

[ H⁺ ] = 10⁻⁴°⁰⁸

= 8.3 x 10⁻⁵

concentration of acid = .3250 M

HA ⇆ H⁺ + A⁻

.325 8.3 x 10⁻⁵ 8.3 x 10⁻⁵

Ka = (8.3 x 10⁻⁵ )² / .325

= 68.9 x 10⁻¹⁰ / .325

= 212 x 10⁻¹⁰ M .

pKa = - log ( 212 x 10⁻¹⁰ )

= 10 - log 212

= 10 - 2.32

= 7.68 .