Pyridine, a substance used as a catalyst in some synthetic reactions is a very weak base its degree of ionization is equal to 0.03% in solution
0.02 mol L -¹. Determine the ionization constant.
Let;s call pyridine just B and we know that is a base.
............B + HOH ==> BH^+ + OH^-
I........0.02........0.02*0.0003 for BHY and 0.02*0.0003 for OH.
Substitute that into the Kb and solve for Kb.
To determine the ionization constant of pyridine (C₅H₅N), we need to use the equation for the degree of ionization:
Degree of ionization = (concentration of ionized form / initial concentration of pyridine) * 100
Given that the degree of ionization is 0.03% and the initial concentration of pyridine is 0.02 mol L⁻¹, we can set up the equation as follows:
0.03% = (concentration of ionized form / 0.02 mol L⁻¹) * 100
To find the concentration of the ionized form, we can rearrange the equation:
(concentration of ionized form / 0.02 mol L⁻¹) = 0.03% / 100
Simplifying the right side of the equation:
(concentration of ionized form / 0.02 mol L⁻¹) = 0.0003
To find the concentration of the ionized form, let's multiply both sides of the equation by 0.02 mol L⁻¹:
concentration of ionized form = 0.0003 * 0.02 mol L⁻¹
concentration of ionized form = 6.0 × 10⁻⁶ mol L⁻¹
Now that we know the concentration of the ionized form, we can find the ionization constant (Ka) using the equation:
Ka = (concentration of ionized form)² / (concentration of unionized form)
Since pyridine is a weak base, we can assume that the concentration of the unionized form is equal to the initial concentration of pyridine, which is 0.02 mol L⁻¹.
Plugging in the values:
Ka = (6.0 × 10⁻⁶ mol L⁻¹)² / (0.02 mol L⁻¹)
Simplifying the equation:
Ka = (3.6 × 10⁻¹¹ mol² L⁻²) / (0.02 mol L⁻¹)
Ka ≈ 1.8 × 10⁻⁹ mol L⁻¹
So, the ionization constant (Ka) for pyridine is approximately 1.8 × 10⁻⁹ mol L⁻¹.