Calculation of Percentage of Pyridine that Forms Pyridinium Ion

Step 1: Write the Equation for the Dissociation of Pyridine

The equation for the dissociation of pyridine in water can be written as:
C5H5N + H2O ⇌ C5H5NH+ + OH-

Step 2: Write the Expression for the Equilibrium Constant

The expression for the equilibrium constant (Kb) for the above reaction can be written as:
Kb = [C5H5NH+][OH-]/[C5H5N]

Step 3: Determine the Concentrations of Pyridine and Pyridinium Ion

In a 0.10 m aqueous pyridine solution, the concentration of pyridine ([C5H5N]) is 0.10 m. Let x represent the concentration of pyridinium ion ([C5H5NH+]). At equilibrium, the concentration of hydroxide ion ([OH-]) can be assumed to be negligible compared to the initial concentration of pyridine.

Therefore, [C5H5NH+] = [OH-] = x and [C5H5N] = 0.10 - x.

Step 4: Substitute the Values in the Expression for Kb

Kb = [C5H5NH+][OH-]/[C5H5N]
Kb = x^2/(0.10 - x)

Step 5: Solve for x

Since Kb is given as 1.7×10^-9, we can substitute the values in the expression and solve for x:
1.7×10^-9 = x^2/(0.10 - x)
x = 1.6×10^-5

Step 6: Determine the Percentage of Pyridine that Forms Pyridinium Ion

The percentage of pyridine that forms pyridinium ion can be calculated by dividing the concentration of pyridinium ion by the initial concentration of pyridine and multiplying by 100%:
% of pyridine that forms pyridinium ion = (x/[C5H5N]) × 100%
% of pyridine that forms pyridinium ion = (1.6×10^-5/0.10) × 100%
% of pyridine that forms pyridinium ion = 0.016%

Therefore, the percentage of pyridine that forms pyridinium ion in a 0.10 m aqueous pyridine solution is 0.016%.