Question

Pyridine (c5h5n) is a particularly foul-smelling substance used in manufacturing pesticides and plastic resins. calculate the ph of a 0.115 m solution of pyridine (kb = 1.4×10-9 ).

Answer 1

Answer is: ph value of pyridine solution is 9.1.

Chemical reaction: C₅H₅N + H₂O → C₅H₅NH⁺ + OH⁻.
c(pyridine - C₅H₅N) = 0.115M.
Kb(C₅H₅N) = 1.4·10⁻⁹.
[C₅H₅NH⁺] = [OH⁻] = x; equilibrium concentration.
[C₅H₅N] = 0.115 M - x.

Kb = [C₅H₅NH⁺] · [OH⁻] / [C₅H₅N].

1.4·10⁻⁹ = x² / (0.115 M -x)

Solve quadratic equation: x = [OH⁻] = 0.0000127 M.
pOH = -log(0.0000127 M) = 4.9

pH = 14 - 4.9 = 9.1.