Question

Calculate the pH of the following solution 3.2 M HC2H3O2 The answer key I have says that x= 7.6 x 10^-5 but I keep getting 5.76 x 10^-5 HELP PLEASE!!

Answer 1

let me solve

CH3COOH ------> CH3COO- + H+

I 3.2 0 0

C -x +x +x

E 3.2-x +x +x

1.75 x 10^-5 = x² / 3.2-x

x² + x1.75 * 10^-5 -5.6 *10^-5

solve this quardratic equation i am using the online soft wear to solve this

x = 7.5 x 10^-3 = [H+]

pH = -log[7.5x 10^-3]

pH = 2.13

there is a another formula to calculate pH which is very easy

i am explaining that also

its acetic acid week acid

there is a direct formula

pH = 1/2(pKa -logC)

pKa of acetic acid 4.756 from the text book

C = concentration = 3.2M

now

pH = 1/2 (4.756 - log[3.2])

pH = 1/2 (4.756 - 0.505)

pH = 2.13

both are matching