Buffer Systems Which of the following, when added to water, can act as a buffer system? For each buffer system, write a balanced equation. (a) HF and NaF (b) HNO3 and KNO3 (c) NH3 and NH4Cl

Question

Buffer Systems

Which of the following, when added to water, can act as a buffer system? For each buffer system, write a balanced equation.

(a) HF and NaF

(b) HNO₃ and KNO₃

(c) NH₃ and NH₄Cl

Accepted Answer

(a) This is a buffer system, because HF is a weak acid and the ionic compound NaF provides a source of its conjugate base, F^–,when it dissolves in water. We can ignore the spectator ion, Na⁺. The following equation shows the conjugate acid-base pair that exists in solution at equilibrium:

[latex]HF(aq)+H_{2}O(l) \xrightleftharpoons[]{} F^{-}(aq)+H_{3}O^{+}(aq)[/latex]

(b) This is not a buffer system, because HNO₃ is a strong acid. Strong acids cannot be components of buffers, because they ionize completely in water and are not in equilibrium with their conjugate bases.

(c) This is a buffer system, because NH₃ is a weak base and its conjugate acid, NH₄⁺, forms when the ionic compound NH₄Cl dissolves in water. We can ignore the spectator ion, Cl^–. The following is a conjugate acid-base pair that will exist at equilibrium in solution:

[latex]NH_{3}(aq)+H_{2}O(l) \xrightleftharpoons[]{} NH^{+}_{4}(aq)+OH^{-}(aq) [/latex]

Question 13.13: Buffer Systems Which of the following, when added to water, ...

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