What is the pK_a for the acid HA if a solution of 0.65 M HA and 0.85 M NaA has a pH of 4.75? A) 5.50

Question

What is the pK_a for the acid HA if a solution of 0.65 M HA and 0.85 M NaA has a pH of 4.75? A)< 4.00 B)4.63 C)4.87 D)5.02 E)> 5.50

Quizplus · Accepted Answer

First, we need to set up the equation for the dissociation of HA:

HA ⇌ H+ + A-

Then, we can use the Henderson-Hasselbalch equation:

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

We know the pH (4.75) and the molarities of A- and HA in the solution. We can use the molarities to calculate the ratio [A-]/[HA]:

[A-]/[HA] = 0.85/0.65 = 1.31

Now we can rearrange the Henderson-Hasselbalch equation to solve for pKa:

pKa = pH - log([A-]/[HA])
pKa = 4.75 - log(1.31)
pKa = 4.63

Therefore, the answer is B.

What Is the PKa for the Acid HA If a Solution