Understanding the Relationship

In any aqueous solution, the product of the hydronium ion concentration ([H3O+]) and the hydroxide ion concentration ([OH-]) is a constant value known as the ion product of water (Kw).

* Kw = [H3O+][OH-] = 1.0 x 10^-14 at 25°C

Calculation

1. Rearrange the equation: To solve for [H3O+], divide both sides of the equation by [OH-]:

[H3O+] = Kw / [OH-]

2. Substitute the values:

[H3O+] = (1.0 x 10^-14) / (2.50 x 10^-4)

3. Calculate:

[H3O+] = 4.0 x 10^-11 M

Answer:

The hydronium ion concentration in the solution is 4.0 x 10^-11 M.