(is this correct)

Question

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

1.  1 M

1.  1 x 10^-6 M

1.  1 x 10^-8 M

1.  1 x 10^-14 M

(is this correct)

Answer 1

Hello, Sdasd,

At 25°C the equilibrium coefficient for water is 1 x 10 ^-14.

K_w = [H₃O⁺][OH^-]

pH is the negative log of the hydrogen(hydronium) ion concentration. Therefore, a pH of 6 means that [H₃O⁺] = 10^-6

K_w = [H₃O⁺][OH^-]

1 x 10 ^-14 = [10^-6][OH^-]

[OH^-] = 10^-8 or 1 x 10^-8 M

[pOH = 8]

Since the equilibrium constant is 10^-14 (at this temperature) it means that the pH and pOH will always sum to 14. If you have pH, you can determine pOH (and thus [OH^-]) easily:

pOH + 6 = 14

pOH = 8

Bob