Question

Which of the acid/base combinations listed below could be used to prepare a buffer solution? Select all that apply:

Check all that apply:
a HPO₄ and KH₂PO₄
b NH₄Cl and NH₃
c HCl and NaCl
d H₂O and LiOH
e HCOOH and NaHCOO

Answer 1

The acid/base combinations that can be used to prepare a buffer solution are HPO₄⁻⁲ and KH₂PO₄, NH₄Cl and NH₃, and HCOOH and NaHCOO because each pair consists of a weak acid or base and its conjugate counterpart.

Step-by-step explanation:

The acid/base combinations that could be used to prepare a buffer solution are those that consist of a weak acid and its conjugate base or a weak base and its conjugate acid. A buffer solution is able to maintain its pH with minor changes when small amounts of acid or base are added.

• HPO₄⁻⁲ and KH₂PO₄: Both are forms of phosphoric acid, with HPO₄⁻⁲ being the conjugate base of H₂PO₄⁻ and KH₂PO₄ providing the acid, H₂PO₄⁻. This pair can make a buffer.
• NH₄Cl and NH₃: NH₄Cl is the salt of the weak base NH₃, providing the conjugate acid NH₄^{+}. This combination forms a buffer solution because NH₄^{+} is the conjugate acid of NH₃.
• HCOOH and NaHCOO: HCOOH is formic acid, a weak acid, and NaHCOO is the sodium salt of the formate ion, HCOO⁻, the conjugate base. This is also a buffer system.

Combinations such as HCl and NaCl do not form a buffer as HCl is a strong acid and NaCl is a salt that does not provide a conjugate weak base. Similarly, H₂O and LiOH do not make a buffer system as they are not an acid/base conjugate pair.