If a water sample has a hydrogen ion concentration of 4.0 x 10-5, what is the concentration of OH-? Is the solution acidic or basic?

To find the concentration of OH- ions, we need to use the ion product of water, Kw, which is equal to [H+][OH-] and is always 1.0 x 10^-14 at 25 degrees Celsius.

Given that the concentration of H+ ions is 4.0 x 10^-5, we can set up the equation:

(4.0 x 10^-5) * [OH-] = 1.0 x 10^-14

Solving for [OH-], we get:

[OH-] = (1.0 x 10^-14) / (4.0 x 10^-5)

[OH-] = 2.5 x 10^-10

So, the concentration of OH- ions is 2.5 x 10^-10.

To determine whether the solution is acidic or basic, we compare the concentrations of H+ and OH- ions. If [H+] > [OH-], the solution is acidic. If [H+] < [OH-], the solution is basic. If [H+] = [OH-], the solution is neutral.

In this case, [H+] (4.0 x 10^-5) is greater than [OH-] (2.5 x 10^-10), so the solution is acidic.