Answer
a) Succinct acid would be a better buffer at pH = 5 because its pK is about 4.2.
b) Piperdine has a pK of 11.12, which means its buffer range is from 10.1 to 12.1. It would therefore not be a very good buffer at pH = 9. Ammonia would be a better buffer at pH = 9 because its pK is 9.25; it would work well as buffer in the range of 8.2 to 10.2.
c) HEPES has a pK of 7.47 and would work well at pH = 7.5. Tris is a basic buffer with a pK of 8.08, so it would only work well in the pH range of 7 to 9.
Work Step by Step
a) Succinct acid would be a better buffer at pH = 5 because its pK is about 4.2.
b) Piperdine has a pK of 11.12, which means its buffer range is from 10.1 to 12.1. It would therefore not be a very good buffer at pH = 9. Ammonia would be a better buffer at pH = 9 because its pK is 9.25; it would work well as buffer in the range of 8.2 to 10.2.
c) HEPES has a pK of 7.47 and would work well at pH = 7.5. Tris is a basic buffer with a pK of 8.08, so it would only work well in the pH range of 7 to 9.
