Problem: Codeine (C18H21NO3) is a narcotic pain reliever that forms a salt with HCl. What is the pH of 0.050 M codeine hydrochloride (pKb of codeine = 5.80)?

FREE Expert Solution

Codeine hydrochloride → salt

HC18H21NO3Cl → HC18H21NO3+ + Cl-


Equilibrium reaction:        HC18H21NO3+(aq) + H2O(l)  C18H21NO3(aq) + H3O+(aq)

***HC18H21NO3+ conjugate acid of C18H21NO3


Step 1: Construct an ICE chart for the reaction.


Step 2: Write the Ka expression and calculate for Ka.

Ka=productsreactantsKa=[C18H21NO3][H3O+][HC18H21NO3+]

Solids and liquids are not included in the expression

Kb=10-pKbKb=10-5.80

Kb = 1.5849x10–6

KwKb=Ka·KbKbKa=1.0×10-141.5849×10-6

Ka = 6.3096x10–9


Step 3: Calculate the equilibrium concentrations.

Ka=xx0.050-xKa=x20.050-x

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Problem Details

Codeine (C18H21NO3) is a narcotic pain reliever that forms a salt with HCl. What is the pH of 0.050 M codeine hydrochloride (pKb of codeine = 5.80)?

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