Question

Calculate the molar concentration of a solution of acetic acid (HOAc) that has a pH of 4.00. (K_a = 1.8 × 10^–5) : 

(A) 1.0 × 10^–3 

(B) 1.0 × 10^–6 

(C) 0.057 × 10^–2 

(D) 0.010

Answer 1

Correct option: (C) 0.057 × 10^–2

Explanation: 

or [HOAc] = 5.56 × 10^–4 M