Calculate the pOH of a nitrous acid solution that contains 3.9 × 10^-⁸ M H₃O⁺ at 25°C. A) 8.41 B) 7.41 C) 6.59 D) 5.59 E) 0.59

Question

Quizplus · Accepted Answer

The first step in solving this problem is to write the balanced chemical equation for the dissociation of nitrous acid:

HNO2 + H2O ⇌ NO2- + H3O+

From this equation, we can see that the nitrous acid will dissociate to form both nitrite ions (NO2-) and hydronium ions (H3O+).

The next step is to write the expression for the equilibrium constant for this reaction, which is known as the acid dissociation constant (Ka):

Ka = [NO2-][H3O+] / [HNO2]

At 25°C, the value of Ka for nitrous acid is 4.5 × 10^-4.

We can use the expression for Ka to calculate the concentrations of NO2- and H3O+ in the solution, and from there we can calculate the pH or pOH of the solution. Since we are asked to calculate the pOH, we will start by finding the concentration of OH- ions in the solution.

First, we need to find the concentration of H3O+ ions, which we can do using the equilibrium constant expression and the initial concentration of HNO2:

Ka = [NO2-][H3O+] / [HNO2]
4.5 × 10^-4 = (x)(x) / (0.039)
x = 0.013 M

So the concentration of H3O+ ions in the solution is 0.013 M.

Next, we need to use the fact that water undergoes autoionization to find the concentration of OH- ions:

Kw = [H3O+][OH-]
1.0 × 10^-14 = (0.013)(x)
x = 7.7 × 10^-13 M

So the concentration of OH- ions in the solution is 7.7 × 10^-13 M.

Finally, we can use the definition of pOH to find the pOH of the solution:

pOH = -log[OH-] = -log(7.7 × 10^-13) = 6.59

Therefore, the correct answer is C.

Calculate the POH of a Nitrous Acid Solution That Contains