Practice MT2 Version 2 #12

[Zellmer, Robert]

Someone asked about question 12 in practice MT2, V2.
It may be confusing.

It gives a pKa of 8.21 for codeine and treats it as an acid.
This is incorrect.  Codeine is a nitrogen base with a pKb of
5.79.  This is EOC problem 16.74 in the textbook.  This
problem is referenced in the solution.  The pKa of 8.21 is
actually for the conj. acid of codeine.

When you take codeine as a medicine it is generally in the
form of an acidic salt (reacted with HCl to make a salt). This
salt contains the conj. acid of codeine with Cl-.

Codeine + HCl -->  CodeineH+ + Cl-

On packages you see it as C18H22NO3*HCl which is
actually (HC18H22NO3)Cl, a salt, containing
(HC18H22NO3)+ with Cl-.

For the practice exam just go ahead and treat it as an
acid as it seems the exam and solutions do.  Just see
if you can get the right answer treating it as an acid.

Dr. Zellmer
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