We’re being asked to determine which of the given solutions are valid ways to make a good buffer.
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
Which of the following are valid ways to make an ammonia/ammonium buffer for use in a laboratory? Explain your choices.
a) Mix equal volumes of 1 M NH3 and 1 M NH4+
b) Mix equal volumes of 1 M NH3 and 0.01 M NH4+
c) Mix equal volumes of 1 M NH3 and 1 HCl
d) Mix some volume of 1 M NH3 and half as much HCl
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