Both HCO3^- and HS^- are amphoteric. Write an equation to show how each substance can act as an acid and another equation to show how each can act as a base.
The correct answer and explanation is :
Both bicarbonate (( \text{HCO}_3^- )) and hydrogen sulfide (( \text{HS}^- )) are amphoteric species, meaning they can act both as acids and as bases, depending on the context. Amphoteric substances have the ability to donate or accept protons (H(^+)).
Bicarbonate (( \text{HCO}_3^- )) as an Acid:
As an acid, ( \text{HCO}_3^- ) can donate a proton (H(^+)) to form carbonate (( \text{CO}_3^{2-} )):
[
\text{HCO}_3^- \rightarrow \text{CO}_3^{2-} + \text{H}^+
]
Bicarbonate (( \text{HCO}_3^- )) as a Base:
As a base, ( \text{HCO}_3^- ) can accept a proton (H(^+)) to form carbonic acid (( \text{H}_2\text{CO}_3 )):
[
\text{HCO}_3^- + \text{H}^+ \rightarrow \text{H}_2\text{CO}_3
]
Hydrogen Sulfide (( \text{HS}^- )) as an Acid:
As an acid, ( \text{HS}^- ) can donate a proton to form sulfide (( \text{S}^{2-} )):
[
\text{HS}^- \rightarrow \text{S}^{2-} + \text{H}^+
]
Hydrogen Sulfide (( \text{HS}^- )) as a Base:
As a base, ( \text{HS}^- ) can accept a proton to form hydrogen sulfide (( \text{H}_2\text{S} )):
[
\text{HS}^- + \text{H}^+ \rightarrow \text{H}_2\text{S}
]
Explanation:
Bicarbonate (( \text{HCO}_3^- )) and hydrogen sulfide (( \text{HS}^- )) are amphoteric because they both have the ability to either donate or accept a proton. This behavior depends on the surrounding conditions. In an environment where there is a higher concentration of H(^+) ions (such as in an acidic solution), both bicarbonate and hydrogen sulfide will act as bases, accepting protons to form their respective acids (( \text{H}_2\text{CO}_3 ) and ( \text{H}_2\text{S} )).
Conversely, in a basic environment where the concentration of H(^+) ions is low, both ( \text{HCO}_3^- ) and ( \text{HS}^- ) can donate protons to form their conjugate bases (( \text{CO}_3^{2-} ) and ( \text{S}^{2-} )). This dual ability to act as either an acid or a base makes these substances amphoteric, which is an important characteristic in various biological and chemical systems, such as in the regulation of blood pH and in sulfur-based chemical reactions.