Question

Codeine C18H21NO3 is a weak organic base. A 5.0 x 10^-3 M solution of codeine has a pH of 9.95. Calculate the value of Kb for this substance. What is the pKb for this base?

Answer 1

Answer:

Kb = $4.45\times10^{-7}\ mol/L$

$p^{Kb}=6.35$

Explanation:

For a weak organic base, the formula to find $p^{OH}$ is given by:

$p^{OH}=p^{K_b}+\log c$

where c is the concentration of base.

Here c= $5\times10^{-3}\ M$

$p^{H}=9.95\\p^{OH}=14-p^{H}=14-9.95=4.05$

Substituting the above values in the formula,we get:

$p^{k_b}=p^{OH}-\log c\\p^{k_b}=4.05-\log (5\times10^{-3})\\p^{K_b}=6.35\\K_b= antilog 6.35=4.45\times10^{-7}\ mol/L$

Hence:

Kb = $4.45\times10^{-7}\ mol/L$

$p^{Kb}=6.35$