We’re being asked to determine which of the given solutions is a good buffer system.
Recall that a buffer can be composed of the following:
• weak base and its conjugate acid
• weak acid and its conjugate base
• weak acid and a strong base
▪ concentration of weak acid > concentration of strong base
• weak base and a strong acid
▪ concentration of weak base > concentration of strong acid
The maximum buffering capacity of a solution is when the pH of the solution is equal to pKa and the buffer range of a solution is pH = pKa ± 1.
• maximum buffering capacity: pH = pKa
• buffering range: pH = pKa ± 1
Given the following information:
H3PO4 Ka1 = 7.5 x 10-3 H2SO4 Ka1 is large
Ka2 = 6.2 x 10-8 Ka2 = 1.2 x 10-2
Ka3 = 4.8 x 10-13
Which one of the following combinations would be the best choice for preparing a buffer of pH 7.0?
A. H3PO4 and NaH2PO4
B. Na2HPO4 and Na3PO4
C. NaH2PO4 and Na2HPO4
D. NaHSO4 and Na2SO4
E. H2SO4 and NaHSO4
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