What is the pH of a buffer solution that is 0.255 mol L^-1 in hypochlorous acid (HClO)and 0.333 mol L^-1 in sodium hypochlorite (NaClO)? The K_a of hypochlorous acid is 3.8 × 10^-8. A)13.88 B)6.46 C)8.49 D)7.30 E)7.54

Question

Quizplus · Accepted Answer

First, we can use the Henderson-Hasselbalch equation to find the pH of the buffer solution:

pH = pKa + log([A-]/[HA])

where pKa is the acid dissociation constant (-log(Ka)), [A-] is the concentration of the conjugate base (sodium hypochlorite), and [HA] is the concentration of the acid (hypochlorous acid).

Plugging in the values:

pH = 7.42 + log(0.333/0.255) 
pH = 7.54

So the pH of the buffer solution is 7.54, which corresponds to answer choice E.

What Is the PH of a Buffer Solution That Is