Ka for this weak acid, Benzoic Acid, (C6H5COOH) is 6.3x10-5. What is the pH of 0.773M solution of benzoic acid

Answer 1

To find the pH of a weak acid solution, we need to use the equation for the dissociation of the weak acid:

C6H5COOH ⇌ C6H5COO- + H+

The Ka expression for this reaction is:

Ka = [C6H5COO-][H+] / [C6H5COOH]

Since the concentration of the benzoate ion (C6H5COO-) is equal to the concentration of H+ in this reaction, we can simplify the expression to:

Ka = [H+]^2 / [C6H5COOH]

Now we can rearrange this expression to solve for [H+]:

[H+] = sqrt(Ka x [C6H5COOH])

[H+] = sqrt(6.3x10^-5 x 0.773)

[H+] = sqrt(4.87x10^-5)

[H+] = 6.98x10^-3

Finally, we can calculate the pH using the equation:

pH = -log[H+]

pH = -log(6.98x10^-3)

pH = 2.155

Therefore, the pH of a 0.773M solution of benzoic acid is approximately 2.155.