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 0.215 m solution of pyridine? (assume that the temperature is 25 °c.)

pH = 9.29

Explanation:

∴ pKb = 8.75 = - Log Kb

⇒ Kb = 1.7783 E-9 = [OH-][C5H5NH+]/[C5H5N]

mass balance:

⇒ C C5H5N = 0.215 M = [ C5H5N ] + [C5H5NH+]

charge balance:

⇒ [OH-] = [C5H5NH+]

⇒ Kb = 1.7783 E-9 = [OH-]² / ( 0.215 - [OH-] )

⇒ [ OH-]² + 1.7783 E-9[OH-] - 3.8233 E-10 = 0

⇒ [OH-] = 1.9552 E-5 M

⇒ pOH = 4.708

∴ 14 = pH + pOH

⇒ pH = 9.29

substituting a hydrogen atom with a halogen in a hydrocarbon:

- the single bond remains single. a is wrong.

- the bond with hydrogen is as strong as with a halogen. c is wrong

- a hydrocarbon is saturated if there is no double bond. we do not know that so d is wrong.

- carbon will always have four valence electrons. e is wrong.

by elimination, the correct answer is b. the boiling point of the new compound increases.