Question

Pyridine is a weak base that is used in the manufacture of pesticides and plastic resins. It is also a component of cigarette smoke. Pyridine ionizes in water as follows: C5H5N+H2O⇌C5H5NH++OH− The pKb of pyridine is 8.75. What is the pH of a 0.460 M solution of pyridine? (Assume that the temperature is 25 ∘C.) Express the pH numerically to two decimal places.

Answer 1

The pH of the solution is 9.46

Step-by-step explanation:

C₅H₅N + H₂O ⇌ C₅H₅NH+OH⁻

I 0.46

C - x +x +x

E 0.46 - x

-LogKb = Pkb

`Kb =10^([-PKb]) = 10^([-8.75]) = 1.778 X 10^(-9)`

`Kb = ([C5H5NH][OH^-])/([C5H5N])`

`1.778 X10^(-9)= (X^2)/(0.46-X) \\\\X^2 = 8.1788 X 10^(-10) - 1.778 X10^(-9)X\\\\X^2 + 1.778 X10^(-9)X -8.1788 X 10^(-10)\\\\X = 2.85977 X 10^(-5) = [OH^-]`

pOH = -Log[OH⁻]

pOH = -Log [2.85977 x 10⁻⁵]

pOH = 4.54

pOH + pH = 14

pH = 14 - pOH

pH = 14 - 4.54

pH = 9.46

Therefore, the pH = 9.46