In an aqueous solution the [OH–] is 2.0 x 10–6 M. What is the [H3O+]?
Question 17 options:
1.0 x 10–7 M
2.0 x 10–6 M
1.0 x 10–8 M
5.0 x 10–9M
To find the [H3O+], we can use the fact that the product of the [H3O+] and [OH-] concentrations in water is constant at 1.0 x 10^-14 at 25 degrees Celsius.
[H3O+] x [OH-] = 1.0 x 10^-14
Given that [OH-] is 2.0 x 10^-6 M, we can substitute this value into the equation and solve for [H3O+].
[H3O+] x 2.0 x 10^-6 = 1.0 x 10^-14
Dividing both sides of the equation by 2.0 x 10^-6, we get:
[H3O+] = (1.0 x 10^-14) / (2.0 x 10^-6)
Simplifying the right side of the equation, we have:
[H3O+] = 0.5 x 10^-8
Therefore, the [H3O+] is 5.0 x 10^-9 M.
Thus, the correct answer is option D: 5.0 x 10^-9 M.
To find the [H3O+] concentration in an aqueous solution with a given [OH-] concentration, you can use the equation for the ion product of water: Kw = [H3O+][OH-].
The value of Kw at 25 degrees Celsius is 1.0 x 10^-14 M^2. Since [OH-] is given as 2.0 x 10^-6 M, you can substitute these values into the equation:
1.0 x 10^-14 M^2 = [H3O+](2.0 x 10^-6 M)
To solve for [H3O+], divide both sides of the equation by 2.0 x 10^-6 M:
(H3O+) = (1.0 x 10^-14 M^2) / (2.0 x 10^-6 M)
Simplifying, you can cancel out one factor of 10^-6:
(H3O+) = (0.5 x 10^-8 M)
Since 0.5 x 10^-8 M is the same as 5.0 x 10^-9 M, the correct answer is option 4: 5.0 x 10^-9 M.