Question

# Which of the following compounds would make the best buffer at pH 7.5? Acetic acid, pKa=...

Which of the following compounds would make the best buffer at pH 7.5?

1. Acetic acid, pKa= 4.76
2. N-tris(hydroxymethyl) methylglycine (Tricine), pKa = 8.15
3. N-2-hydroxyethylpiperazine-N’-ethansulfonic acid, pKa2= 7.6
4. Glycine, pKa2= 9.9
5. Tris(hydroxymethyl)aminomethane (Tris), pKa = 8.3

I believe 3 is the correct answer and therefore I am trying to answer the below question with this information.

Using the answer that you selected from question 1 above:

a. Explain how you would make the buffer starting with 1M HA and 1M A- forms of your buffer. Show all work.

7.5 = 7.6 + log ([A-]/[HA])

([A-]/[HA]) = 0.9048 --> therefore the ratio would be a 9:10 acid:base ratio, I think? Can you please let me know if I'm on the right track and also help with the question part b to create a buffer with a pH of 8.1? Thanks!!!

b. You also want to create a buffer with a pH of 8.1. Calculate how many mL of 1M NaOH/HCl you must add to the buffer in part a to achieve this goal. Show all work.

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