Please choose the write answer

Question

What is the PH of 0.010 M solution of acetic acid? Ka=1.8*10^-5

a)2.74

b)4.74

c)6.74

d)3.37

Answer 1

Let acetic acid be HAc

HAc ==> H⁺ + Ac^-

Ka = [H⁺][Ac^-]/[HAc]

1.8x10^-5 = [H+][Ac-]/[HAc]

1.8x10^-5 = (x)(x)/0.01-x (assume x is small and neglect it in denominator)

x2 = 1.8x10^-7

x = 4.24x10^-4 M = H⁺ = Ac-

pH = -log [H⁺] = -log 4.24x10^-4

pH = 3.37 so (d) is the RIGHT answer