Question

A sodium hydroxide (NaOH) solution has a molar concentration of 0.00250 M. Calculate the [H₃O⁺], [OH⁻] and pH of the solution. (Remember that Kw = 1.0x10⁻¹⁴M²)."

Answer 1

The [OH-] in a 0.00250 M NaOH solution is 0.00250 M, the [H3O+] is calculated to be 4.0 x 10^-12 M using the water ion-product, and the pH is approximately 11.40 indicating a basic solution.

Step-by-step explanation:

To calculate the hydroxide ion concentration [OH-], the molarity of the NaOH solution can be directly used because NaOH is a strong base and completely dissociates in water. Therefore, the [OH-] is 0.00250 M. To find the hydronium ion concentration [H3O+], we use the ion-product constant for water (Kw) which is 1.0 x 10-14 M2 at 25 ℃. The formula to calculate [H3O+] is given by Kw divided by [OH-].

Calculations:

[H3O+] = Kw / [OH-] = 1.0 x 10-14 / 0.00250 = 4.0 x 10-12 M

Lastly, to find the pH of the solution we use the formula pH = -log([H3O+]). Note that because the concentration of H3O+ is very low, the pH will be high, indicating a basic solution.

Calculations:

pH = -log(4.0 x 10-12) ≈ 11.40