Sapling Week 2 #5

[Lauren To 1E]

The K_b for an amine is 9.748×10−5. What percentage of the amine is protonated if the pH of a solution of the amine is 9.947 ? Assume that all OH− came from the reaction of B with H2O.

How would you find the percentage of the amine that's protonated for this question? I found pOH, [OH-], and [NH3] but I'm not sure how to use this information to find the percentage

[KatarinaReid_3H]

Looks like you have all the necessary data. The formula would be [OH-]/[NH3]initial x 100%. Basically, you want to know how much hydroxide was created in comparison to the amount of initial NH3 you have to find out how much NH3 protonated(or was willing to gain an extra H+ to make OH-).

[Lauren To 1E]

I found the equilibrium concentration of NH₃ using K_b not the initial concentration so I'm still not sure which values I would use to find the percentage protonated because I don't have an initial value for [NH₃]

[Katie_Dinh_1D]

I also had a hard time with this question too, but I ended up just solving for the initial value of NH3. Since they give us the pH we can solve for the POH using pH+pOH=14. After this, pOH=-log[OH-], so we can get the concentration for OH- through algebra. If we set up an ice chart, we know that Kb=x^2/B-x. Since we have the concentration for OH- we would also have the value for x. From here, I just solved for B, the initial value, but plugging in the given Kb and x. Hope this helped!

[Breanna Ouyang 1I]

This question is working backwards in a way. After being given the pH, you then find the pOH and the molar concentration of OH- ions (which is x in the ICE table). I think you then use that value to find the initial concentration of the amine and divide x by it for percent protonation.

[905565862]

Could someone write out their steps? I did the same thing you guys are describing but my answer is not correct.

[Brooklyn Burgess 3L]

Could someone write out their steps? I did the same thing you guys are describing but my answer is not correct.

Hi, here I did the problem above. I think the part that made this problem confusing was knowing that to find the % amine protonation we have to do this: ([BH+]/[BH+] + [B]) x 100%. Hope this helps!

[trevina_brown_2A]

Hi, here I did the problem above. I think the part that made this problem confusing was knowing that to find the % amine protonation we have to do this: ([BH+]/[BH+] + [B]) x 100%. Hope this helps![/quote]

This was very helpful thank you !

[Deivy Gonzalez 3H]

I was stuck for the longest on how to begin but thankfully you had a step by step process. I really appreciate it.