To find the Ka value for the conjugate acid of pyridine (C5H5NH+), we can use the relationship between Ka and Kb for a conjugate acid-base pair. The formula we use is:
Ka × Kb = Kw
Where Kw is the ion product of water, which is approximately 1.0 x 10^-14 at 25°C.
Given that the Kb value for pyridine (C5H5N) is 1.7 x 10^-9, we can rearrange the formula to find Ka:
Ka = Kw / Kb
Substituting the known values:
- Kw = 1.0 x 10^-14
- Kb = 1.7 x 10^-9
Now plug in the numbers:
Ka = (1.0 x 10^-14) / (1.7 x 10^-9)
Calculating this gives:
Ka ≈ 5.88 x 10^-6
Thus, the Ka value for C5H5NH+ is approximately 5.88 x 10^-6. This indicates that C5H5NH+ is not a strong acid, but it can still donate protons in solution, making it a weak acid.