Boric acid frequently is used as an eyewash to treat eye infections.The pH of a 0.050 M boric acid solution is 5.28.What is the value of K_a?

Question

Quizplus · Accepted Answer

The Ka value for boric acid (H3BO3) can be calculated using the equation: 
Ka = [H+][H2BO3-]/[H3BO3]

In this case, the pH of the solution can be used to find the [H+]:
pH = -log[H+]
5.28 = -log[H+]
[H+] = 1.6 x 10^-6 M

Assuming that the dissociation of boric acid is small, the concentration of H2BO3- can be approximated as equal to the concentration of H3BO3:
[H2BO3-] = [H3BO3] = 0.050 M

Substituting into the Ka equation:
Ka = (1.6 x 10^-6)^2 / 0.050
Ka = 5.5 x 10^-10

Therefore, the answer is B: 5.5 x 10^-10.

Boric Acid Frequently Is Used as an Eyewash to Treat ×\times×

Boric Acid Frequently Is Used as an Eyewash to Treat $\times$