what is pH of 8.8 x 10^-8 M HCl

Answer 1

Because the concentration of HCl is so low, we must take into consideration the contribution of H⁺ provided from H₂O molecules when determining the pH.

K_w = 1x10^-14 and [H⁺] = 1x10^-7 M

8.8x10^-8 M HCl and [H^+] = 8.8x10^-8 M

Total [H⁺] = 1x10^-7 M + 8.8x10^-8 M = 1.90x10^-7

pH = -log [H⁺] = -log 1.90x10^-7

pH = 6.72 (2 sig. figs.)

Answer 2

Since HCl is a strong acid, it dissociates into H+ + Cl- 100%. Thus, the [H+] = [HCl], which is 8.8 x 10^-8 M.

pH = -log [H+] = - log (8.8 x 10^-8) = 7.056 M or 7.1 M (2 sig figs)