Question

05124120 Benzoic acid or (B204) is a weak aud ike of 66.246x 10") often used in organic Chemistry - What is the pH of a 0.026 M solution of sodium benzoate Bz O Na?

please show all the work!

Answer 1

Given C6H5COONa is the salt of a strong base (NaOH) and weak acid (C6H5COOH), and thus the salt in aqueous solution will have a pH.

The hydrolysis of the cyanide ion is as follows,

C6H5COO- + H2O ==> C6H5COOH + OH-

Ka value of C6H5COOH is given, Ka = 6.28 x 10-5

Using the formula Kw = KaKb

Kb = Kw/kb

Kb = 1 x 10-14/ 6.28 x 10-5

Kb = 0.15924 x 10-9

Kb = 0.15924 x 10-9= [C6H5COOH] [OH-]/ [ C6H5COO-]

0.15924 x 10-9= (x)(x)/0.026M                  where, [C6H5COOH] = x, [OH-] = x, C6H5COO- = 0.026 M

x2 = 6.125 x 10-9

x2 = 61.25 x 10-10

x =[OH-]= 7.826 x 10-5

pOH = -log [OH-]

pOH = -log [7.826 x 10-5]

pOH = 4.1064

14 = pH + pOH

pH = 14 – pOH

pH = 14 – 4.1064

pH = 9.8936