Which base listed below would be the best to creat a buffer having a pH of 5.0230?
hydrazine, Kb = 8.90e-7
methylamine, Kb = 3.70e-4
ethanolamine, Kb = 3.20e-5
pyridine, Kb = 1.40e-9
Convert each of the Kb values to pKb = -log Kb and convert those to pKa by
pKa + pKb = 14
The closest pKa values to the desired pH is the one you want.
To determine which base is the best for creating a buffer with a pH of 5.0230, we need to consider the pKa values of the bases. The pKa value represents the acidity of the conjugate acid of a base. For a buffer solution, we want the pKa to be as close as possible to the desired pH.
First, let's convert the given pH value into pKa by subtracting it from 14 (since pKa + pH = 14). Therefore, pKa = 14 - pH = 14 - 5.0230 = 8.9769.
Now, let's compare the pKa values of the bases listed:
1. Hydrazine (Kb = 8.90e-7): To find the pKa of hydrazine, we need to take the negative logarithm (base 10) of the Kb value. pKa = -log(Kb) = -log(8.90e-7) ≈ 6.05.
2. Methylamine (Kb = 3.70e-4): Similarly, pKa = -log(Kb) = -log(3.70e-4) ≈ 3.43.
3. Ethanolamine (Kb = 3.20e-5): pKa = -log(Kb) = -log(3.20e-5) ≈ 4.50.
4. Pyridine (Kb = 1.40e-9): pKa = -log(Kb) = -log(1.40e-9) ≈ 8.85.
From the above comparisons, we can see that the base with the pKa closest to 8.9769 (the desired pH converted to pKa) is pyridine, with a pKa of 8.85. Therefore, pyridine would be the best base to create a buffer with a pH of 5.0230.