Sapling Week 2 Question 5

[Stuti Pradhan 2J]

For #5 on the week 2 Sapling hw, the question is as follows:

The Kb for an amine is 5.266×10−5. What percentage of the amine is protonated if the pH of a solution of the amine is 9.572 ? Assume that all OH− came from the reaction of B with H2O.

I was wondering how to tell that this solution is at equilibrium. Is it because the problem states that the amine is protonated and therefore we can assume the solution is at equilibrium? Or because the OH- came from the reaction, so we know a reaction must have occurred?

Thanks for your help!

[Hayden Lee 1C]

Hi there!

I believe that we assume the reaction is at equilibrium as a result of the fact that the problem states the amine is protonated, meaning the reaction has already occurred. I wish I could be more thorough, but that's all the info I'm able to provide!

[HannahRobinson3L]

Hello! for a lot of the problems, it really is just a matter of context. The fact that they give you Kb and mention protonation are good indicators. In the context of this class, we will probably only be asked to find how much has been protonated at equilibrium though.