Achieve number 5 week 2

[Isabella Nassir 2B]

I keep having trouble with this question. First, I converted pH to pOH and then turned it into [OH-]. but then I seem to get confused about the steps and calculations afterward. Where do I go after this?

Question: The Kb for an amine is 4.480×10−5. What percentage of the amine is protonated if the pH of a solution of the amine is 9.109 ? Assume that all OH− came from the reaction of B with H2O.

[Christina Gigoux 1D]

If you have an ICE box set up, the value you got for [OH-] would be the final value for [OH-] and this is what we usually consider our "x" value. Your ice box would look something like this (A being the initial concentration of amine):

I: A 0 0
C: -x +x +x
E: A - x x x

If you use the value you got for [OH-] as x, then you could then use the Kb to solve for A. After you know this initial concentration, you can calculate the % protonation.

[RossLechner3E]

As stated above, with the OH- and an ICE box you can find the required concentrations to solve for percent protonation. It is important, however, to not just use the final concentration of the amine in the division. You need to use the initial concentration which can be obtained by adding the amine final concentration and the protonated amine together then divide the protonated amine by that quantity and that will yield the percent protonation.

[Aaron Kwan 3B]

Does it also suffice to calculate percent protonation using the initial value of B?