An unknown weak acid with a concentration of 0.097 M has a pH of 1.80. What is the Ka of the weak acid?

To find the Ka of the weak acid, we first need to find the concentration of H+ ions using the pH value. The formula to find the concentration of H+ ions is:

[H+] = 10^-pH

Substituting the given pH value:

[H+] = 10^-1.80 = 0.0158 M

Next, we use the formula for the ionization of a weak acid:

HA ⇌ H+ + A-

Where HA is the weak acid, H+ is the hydrogen ion, and A- is the conjugate base. At equilibrium, the concentrations of these species are related by the acid dissociation constant Ka:

Ka = [H+][A-]/[HA]

We know that the concentration of H+ ions is equal to the concentration of A- ions, and the concentration of HA is given as 0.097 M. So we can substitute these values into the formula:

Ka = (0.0158)(0.0158)/0.097 = 0.0026

So, the Ka of the weak acid is approximately 0.0026.