Question

(a) Would phosphoric acid or succinic acid be a better buffer at pH5?

(b) Would ammonia or piperidine be a better buffer at pH 9?
(c) Would HEPES or Tris be a better buffer at pH 7.5?
A- succinic acid,
B- ammonia,
C- HEPES
Please expain why these are the answers.

Answer 1

Succinic acid would be a better buffer at pH 5 compared to phosphoric acid. Ammonia would be a better buffer at pH 9 compared to piperidine. HEPES would be a better buffer at pH 7.5 compared to Tris.

Step-by-step explanation:

In order to determine which acid would be a better buffer at pH 5, we need to compare their pKa values. The pKa of a weak acid indicates its acidity and its ability to donate protons. The lower the pKa, the stronger the acid. Phosphoric acid has three acidic protons with pKa values of 2.15, 7.20, and 12.32. Succinic acid, on the other hand, has two acidic protons with pKa values of 4.16 and 5.60.

Since the pH of a buffer is determined by the ratio of the weak acid to its conjugate base, choosing an acid with a pKa close to the desired pH is ideal. In this case, succinic acid with a pKa of 5.60 would be the better buffer at pH 5 because its pKa is closer to the desired pH.

Similarly, to determine which base would be a better buffer at pH 9, we need to compare their pKb values. The higher the pKb, the stronger the base. Ammonia has a pKb of 4.74, while piperidine has a pKb of 2.86. Since we are looking for a base that is effective at pH 9, ammonia, with a higher pKb, would be the better buffer.

Lastly, to determine which acid would be a better buffer at pH 7.5, we can compare the pKa values of HEPES and Tris. HEPES has a pKa of 7.55, while Tris has a pKa of 8.07. Since we want a buffer that is effective at pH 7.5, HEPES would be the better choice due to its closer pKa value to the desired pH.