The ionization constant of an acid, HX is 1 x 10^-5. When a mixture of 0.100 mol HXand 0.100 mol of NaX is diluted to a volume of one liter by addition of wate, the pH of the resulting solution is very nearly

a. 7
b. 6
c. 5
d. 4

Ka for HX = (H^+)(X^-)/(HX)

Solve for (H^+) and convert to pH.

To determine the pH of the resulting solution, we need to calculate the concentration of H+ ions in the solution.

Given that the ionization constant (Ka) of acid HX is 1 x 10^-5, we can write the equilibrium equation for the dissociation of HX as:
HX ⇌ H+ + X-

The initial concentration of HX is 0.100 mol, and since it dissociates completely, the concentration of H+ ions will also be 0.100 mol.

When NaX is added to the solution, it will dissociate completely into Na+ and X-. Since the concentration of NaX is also 0.100 mol, the concentration of X- ions will also be 0.100 mol.

Therefore, the total concentration of X- ions will be 0.100 mol.

To calculate the concentration of H+ ions, we need to consider the common ion effect, which states that the presence of a common ion (in this case, X-) will suppress the ionization of the acid. It means that the concentration of H+ ions will be decreased due to the presence of X- ions.

The resulting concentration of X- ions will be the sum of the initial concentration of X- ions and the concentration of X- ions from NaX, i.e., 0.100 + 0.100 = 0.200 mol.

To calculate the concentration of H+ ions, we subtract the concentration of X- ions from the initial concentration of H+ ions:
[H+] = 0.100 - 0.200 = -0.100 mol

However, the concentration of H+ ions cannot be negative. This indicates that all of the H+ ions will be neutralized by the X- ions.

When all H+ ions are neutralized, the resulting solution will have a pH equal to the pOH. Since pOH = -log(OH-), and in this case, the concentration of OH- ions is equal to the concentration of X- ions (0.200 mol), we can calculate the pOH as follows:
pOH = -log(0.200) ≈ 0.699

Finally, to find the pH of the resulting solution, we use the fact that pH + pOH = 14:
pH = 14 - pOH ≈ 14 - 0.699 ≈ 13.301

Since the pH scale ranges from 0 to 14, and the resulting solution has a pH of approximately 13.301, the answer is: a. 7, as it is the closest option.