The conjugate base of sulfuric acid (H2SO4)
Correct Answer
The conjugate base of sulfuric acid (
H2SO4H2SO4) is the hydrogen sulfate ion (
HSO4−HSO4−).
Explanation
According to the Brønsted-Lowry theory of acids and bases, an acid is a substance that can donate a proton (
H+H+ion), while a base is a substance that can accept a proton. A conjugate acid-base pair consists of two species that differ from each other by the presence or absence of a single proton. The species that remains after an acid has donated its proton is called its conjugate base.
Sulfuric acid (
H2SO4H2SO4) is a strong, diprotic acid, meaning it can donate two protons in successive steps. To find its conjugate base, one must consider the first dissociation, where the parent acid donates its first proton. The process can be represented by the following equilibrium reaction:
H2SO4(aq)⇌H+(aq)+HSO4−(aq)H2SO4(aq)⇌H+(aq)+HSO4−(aq)In this reaction, sulfuric acid (
H2SO4H2SO4) acts as the Brønsted-Lowry acid by donating a proton (
H+H+). The species that is formed after this donation is the hydrogen sulfate ion,
HSO4−HSO4−. Therefore, the hydrogen sulfate ion is the conjugate base of sulfuric acid.
It is important to note that the hydrogen sulfate ion is itself an acid, as it can donate its remaining proton in a second dissociation step to form the sulfate ion (
SO42−SO42−):
HSO4−(aq)⇌H+(aq)+SO42−(aq)HSO4−(aq)⇌H+(aq)+SO42−(aq)In this second reaction, the hydrogen sulfate ion (
HSO4−HSO4−) acts as the acid, and the sulfate ion (
SO42−SO42−) is its conjugate base. Thus, while
HSO4−HSO4−is the conjugate base of
H2SO4H2SO4, it is also the conjugate acid of
SO42−SO42−. This ability to act as both an acid and a base makes the hydrogen sulfate ion an amphiprotic species. However, when asked for the conjugate base of sulfuric acid, the correct answer is always the species formed after the loss of the first proton.thumb_upthumb_down
