Be sure to answer all parts. What is the [ H 3 O + ] and the pH of a benzoic aci

Question

Be sure to answer all parts.

What is the [H3O+] and the pH of a benzoic acid-benzoate buffer that consists of 0.12 M C6H5COOH and 0.31 M C6H5COONa? (Ka of benzoic acid = 6.3 × 10?5) Be sure to report your answer to the correct number of significant figures.

[H3O+] = __ x 10 __ M

pH = __

Be sure to answer all parts.

What is the [H3O+] and the pH of a benzoic acid-benzoate buffer that consists of 0.12 M C6H5COOH and 0.31 M C6H5COONa? (Ka of benzoic acid = 6.3 × 10?5) Be sure to report your answer to the correct number of significant figures.

[H3O+] = __ x 10 __ M

pH = __

Explanation / Answer

The ka of Benzoic acid (C6H5COOH) is 6.3 x 10-5

Now, Ka = 6.3 x 10-5

So, pKa = - log Ka
= - log (6.3 x 10-5)
= 4.20

Using Henderson hasselbalch equation;

pH = pKa + log { [salt] / [acid}
= pKa + log { [C6H5COONa] / [C6H5COOH] }
= 4.20 + log (0.31 / 0.12)
= 4.20 + log (2.58)
= 4.20 + 0.41
? = 4.61
? = 4.6 (upto 2 sig dig)

Now, - log [H3O+] = pH
or, - log [H3O+] = 4.6
or, [H3O+] = 10-4.6
or, [H3O+] = 2.5 x 10-5 M (upto 2 sig dig)

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