Question

Which of the following weak acids would be the best to use to make a buffer solution of pH = 4.8?

a. Acetic acid (Kₐ = 1.75 × 10⁻⁵)
b. Formic acid (Kₐ = 1.8 × 10⁻⁴)
c. Dihydrogen phosphate (Kₐ = 6.2 × 10⁻⁸)
d. Nitrous acid (Kₐ = 4.5 × 10⁻⁴)

Answer 1

The best weak acid to make a buffer solution with a pH of 4.8 is acetic acid because its pKa value of 4.74 is closest to the desired pH, making it most effective in creating a stable buffer solution.

Step-by-step explanation:

To determine the best weak acid to use for making a buffer solution with a pH of 4.8, we must consider the pKa values of the given acids. A buffer is most effective when the pKa of the acid is closest to the desired pH because the ratio of the acid to its conjugate base will be close to 1.

In this case, we are comparing the pKa values of acetic acid (pKa = 4.74), formic acid (pKa = 3.74), dihydrogen phosphate (pKa = 7.21), and nitrous acid (pKa = 3.35). Since the pKa of acetic acid is closest to the target pH of 4.8, it would be the best choice for creating this buffer solution. Other factors, such as chemical compatibility and availability, may also play a role, but pKa is the principal factor in this decision.