The ka of acetic acid ch3co2h is 1.8 x10-5. what is the ph

You must know the concentration of the acetic acid. Suppose the concentration is 0.1 M. The solution is as follows:

            CH₃COOH → CH₃COO⁻ + H⁺
 I                  0.1               0              0
C                 -x                +x            +x
E              0.1 - x             x               x

Ka = (x)(x)/(0.1 - x)
1.8×10⁻⁵ = x²/(0.1 - x)
Solving for x,
x = 1.333×10⁻³ = H⁺

pH = -log[H⁺] = -log(1.333×10⁻³)
pH = 2.88