Question

What is the pH of a 0.050 M triethylamine, (C2H5)3N, solution? Kb for triethylamine is 5.3 ´ 10-4. Question options: 1) 11.69 2) 8.68 3) 5.32 4) 2.31 5) < 2.0

Answer 1

the pH of a 0.050 M triethylamine, is 11.70

For triehtylamine,
`(C_(2)H_(5))_(3)N`, the reaction will be

`(C_(2)H_(5))_(3)N + H_(2)O ---\ \textgreater \ ( C_(2)H_(5))_(3)NH^(+) + OH^(-)`

and we know, pH = -log[H+] and pOH = -log[OH-]Also, pOH + pH = 14Now, the Kb value = 5.3 x 10^-4

And
`kb = (( [( C_(2)H_(5))_(3)NH^(+) ]* OH^(-) ))/([( C_(2)H_(5))_(3)N])`

thus, [OH-] =(5.3 ^ 10-4) ^2 / 0.050

=0.00516 M

Thus, pOH = 2.30
pH = 14 - pOH = 11.7