Ashley Week 3 Workshop Wkst + Key

[Chem_Mod]

Hi everyone,

Attached below is the worksheet I will be going over in my workshop today from 3-4pm in Young Hall 4222D1. I will be posting a key right after my workshop. If you have any questions, please feel free to reach out!

Update: Key is posted!

[Raya Amin 2A]

Hi!

I'm a little confused on question 3c-e. For part c, when it asks what substance is being combined with NH3 to make the buffer solution, I thought that buffer solutions are made up of a weak base and its conjugate acid salt, but none of the options contain this. How would you determine the substance in Solution X using the concentrations and pH given?

Thank you!

[Chem_Mod]

Hi!

I'm a little confused on question 3c-e. For part c, when it asks what substance is being combined with NH3 to make the buffer solution, I thought that buffer solutions are made up of a weak base and its conjugate acid salt, but none of the options contain this. How would you determine the substance in Solution X using the concentrations and pH given?

Thank you!

Hi! For part c, you actually do not need the concentration or pH. You are right that a buffer is made up of a weak base and its conjugate acid. Since we are trying to produce the conjugate acid, the question is asking what substance can you add so that the conjugate acid is formed. If you add HCl (a strong acid), this will form the conjugate acid NH4+. Hope this helps and please let me know if you have any other questions!

[Damian Hernandez 1J]

Hi! I understand the answer to 2a, but I'm a little stuck on the logic. Would you be able to walk through it?

[Chem_Mod]

Hi! I understand the answer to 2a, but I'm a little stuck on the logic. Would you be able to walk through it?

You actually don't need to know how to create a buffer for this upcoming midterm! But for this problem, an ideal buffer is created when the pH = pKa. This is based on the Henderson-Hasselbalch equation (which you also don't need to know) but when the pH = pKa, the [A-] = [HA], which would create an ideal buffer. So when selecting the buffer system, you need to choose the buffer system that has a pKa value closest to the pH. Hope this helps!