Textbook Problem 6D.5(a)

[Amy Xia 1J]

Hi,

Does anyone know how to solve this problem? I tried a few times but still can't get the right answer... [The answer said pH = 11, pOH = 3, and the percent protonation is 1.8%]

Calculate the pH, pOH, and percentage protonation of solute in each of the following aqueous solutions: (a) 0.057M NH3(aq.), given that the pKa of its conjugate acid is 8.21.

Thank you!!!

[Vy Le 1G]

Hi,

I went about the problem by first writing the chemical reaction for NH3 and water which makes NH4+ and OH- (since NH3 is a weak base). Then, I went to the table the textbook referred us to and found the Kb value. After finding the Kb value, I set up an ICE table and solved for x (which is actually OH-). Then, I took the -log (x) to find the pOH. Using 14-pOH, you should have the pH too. Finally, I took (x/initial concentration) x 100% to get the % protonation.

Hopefully this is somewhat easy to follow and clarifies the problem!

[Michelle_Duong_3H]

Hello,

I initially had trouble with this problem too, and I think that it's due to the wording. The pKa value that they give us is only for part (d)--it doesn't apply to the other parts of the problem. Therefore after you set up your ICE table, you would go to the table in the textbook to find the Kb of ammonia rather than calculate it from the pKa.

Hope this helps!

[Amy Xia 1J]

Hello,

I initially had trouble with this problem too, and I think that it's due to the wording. The pKa value that they give us is only for part (d)--it doesn't apply to the other parts of the problem. Therefore after you set up your ICE table, you would go to the table in the textbook to find the Kb of ammonia rather than calculate it from the pKa.

Hope this helps!

Gotta! Thank you!!! Appreciate it!