Answer:
HEPES.
Explanation:
Hello,
In this case, considering the given options, and the pH requirement of 7.5, considering the Henderson-Hasselbach equation:
[tex]pH=pKa+log(\frac{[base]}{[acid]})[/tex]
The best buffer is that having the closest pKa to the required pH, thus, for the given Ka, we obtain:
[tex]pKa_{MES}=-log(Ka_{MES})=-log(7.9x10^{-7})=6.10\\\\pKa_{HEPES}=-log(Ka_{HEPES})=-log(3.2x10^{-8})=7.49\\\\pKa_{Formic \ acid}=-log(Ka_{Formic \ acid})=-log(1.8x10^{-4})=3.74\\\\pKa_{Acetic\ acid}=-log(Ka_{Acetic\ acid})=-log(1.8x10^{-5})=4.74\\\\pKa_{Tris}=-log(Ka_{Tris})=-log(6.3x10^{-9})=8.2[/tex]
Therefore, the best buffer is the HEPES since its pKa is almost the required pH.
Regards-
