Definition of acidic solution

Question

Which of the following is a correct definition of an acidic aqueous solution?

I. A solution where [H⁺]>[OH]^- II. A solution with pH<7

A. I, only

B. Both I and II

C. II, only

D. Neither I nor II

Answer 1

A. I, only

The reason II is not correct is because at certain temperatures the Ka for H2O is NOT 1x10^-14. Take for example a situation where Kw = 1x10^-13.

Kw = H⁺ + OH^-

1x10^-13 = (x)(x) = x²

x = 3.16x10^-7 = [H⁺] = [OH^-]

pH = -log 3.16x10^-7

pH = 6.50 and this would be a NEUTRAL solution since [H⁺] = [OH^-] even though the pH is <7