Question

At 25°C, aqueous solutions with a pH of 6 have a hydroxide ion concentration, [OH^-], of

• 1 M

• 1 x 10^-6 M

• 1 x 10^-8 M

• 1 x 10^-14 M

pick one answer choice and explain

Answer 1

use the concept of Kw.

$Kw = [H^+][OH^-] = 1×10^{-14} @ 25 C$

If pH = 6, then$[H^+] = 1×10^{-6} mol/L,$ so by

substitution $1×10^{-14} = (1×10^{-6})[OH^-]$

$[OH] = \frac{1×10^{-14}}{1×10^{-6}}= 1×10^{-8} mol/L$