HW 2, Question 5

[Abby Freeman 1C]

For question 5:

The Kb for an amine is 3.384×10−5. What percentage of the amine is protonated if the pH of a solution of the amine is 9.250? Assume that all OH− came from the reaction of B with H2O.

After getting the concentrations of OH- and BH+, how do you solve for B? What is the equation to use?

[Bernard Ayran 2F]

You would have to use the basicity constant Kb = [BH+][OH-]/ [B]. You can rearrange the equation to solve for B. After finding B you can find the protonated amine percentage through the equation ([BH+] / [BH+] + [B]) * 100.

[Brandy_Lopez_1C]

To solve this, you need to use your pH to find the pOH and [OH-]
pOH = 14.00-pH
[BH+] = [OH-] = 10^pOH

Then, find your [B] using kB
[B] = [BH+][OH−]/kb

After you find you [B] use the % amine protonated formula
% amine protonated=[BH+]/[BH+][B] × 100


Hope that helps!