Question

Which of the following is a set of amphiprotic species? (a) \(\mathrm{H}_{3} \mathrm{O}^{+}, \mathrm{HCO}_{3}^{-}, \mathrm{HSO}_{4}^{-}\) (b) \(\mathrm{H}_{2} \mathrm{O}, \mathrm{H}_{2} \mathrm{PO}_{2}^{-}, \mathrm{HCO}_{3}^{-}\) (c) \(\mathrm{H}_{2} \mathrm{O}, \mathrm{HPO}_{3}^{2-}, \mathrm{HPO}_{4}^{2-}\) (d) \(\mathrm{H}_{2} \mathrm{O}, \mathrm{H}_{2} \mathrm{PO}_{3}^{-}, \mathrm{H}_{2} \mathrm{PO}_{4}^{-}\)

Short answer

The correct set of amphiprotic species is option (d): H_{2}O , H_{2}PO_{3}^{-} , H_{2}PO_{4}^{-} .

Step-by-step solution

Understand Amphiprotic Species

Amphiprotic species are those that can act as both an acid (proton donor) and a base (proton acceptor). This means they can both donate a proton to become a conjugate base and accept a proton to become a conjugate acid.

Analyze Option A

- ** H_{3}O^{+} ** is the hydronium ion and acts as an acid, not amphiprotic. - ** HCO_{3}^{-} ** can donate a proton to become CO_{3}^{2-} or accept a proton to become H_{2}CO_{3} , thus it is amphiprotic. - ** HSO_{4}^{-} ** can donate a proton to become SO_{4}^{2-} or accept a proton to become H_{2}SO_{4} , making it amphiprotic.

Analyze Option B

- ** H_{2}O ** can donate a proton to form OH^{-} or accept a proton to form H_{3}O^{+} , making it amphiprotic. - ** H_{2}PO_{2}^{-} ** is not typically known to donate another proton, hence it is not amphiprotic. - ** HCO_{3}^{-} ** is amphiprotic as analyzed earlier.

Analyze Option C

- ** H_{2}O ** is amphiprotic (as analyzed before). - ** HPO_{3}^{2-} ** is not commonly recognized as amphiprotic. - ** HPO_{4}^{2-} ** can donate a proton to PO_{4}^{3-} or accept a proton to form H_{2}PO_{4}^{-} , so it is amphiprotic.

Analyze Option D

- ** H_{2}O ** is amphiprotic (as explained). - ** H_{2}PO_{3}^{-} ** can technically donate a proton to HPO_{3}^{2-} or accept another proton to form H_{3}PO_{3} , but its amphiprotic nature is not as commonly referenced, depending on context. - ** H_{2}PO_{4}^{-} ** can donate a proton to become HPO_{4}^{2-} or accept a proton to become H_{3}PO_{4} , making it amphiprotic.

Determine the Correct Set

Based on the analyses, option (d) includes all amphiprotic species: H_{2}O , H_{2}PO_{3}^{-} , and H_{2}PO_{4}^{-} . Other options contain species that are not amphiprotic, so the correct answer is option D.

Key concepts

Acid-Base Chemistry

Delving into the world of acid-base chemistry reveals a fascinating realm of substances that participate in proton ( H^+ ) exchanges. Acids are substances that can donate protons, while bases are those that have the ability to accept them. This equilibrium of donation and acceptance defines the core concept of acid-base reactions.

In the context of amphiprotic species, these substances hold a special place as they can act as both an acid and a base. An amphiprotic species can donate a proton to another species, functioning as an acid, or accept a proton, acting as a base. For example, water ( H_2O ) can act as an acid when it donates a proton to become the hydroxide ion ( OH^- ), or as a base when it accepts a proton to form the hydronium ion ( H_3O^+ ). This dual ability makes amphiprotic species versatile players in acid-base chemistry.

Acid-base chemistry is foundational to understanding complex chemical reactions in aqueous solutions, making it crucial for students to grasp this balance of proton transfers.

Proton Transfer

Proton transfer is a fundamental process in acid-base reactions, whereby protons are exchanged between molecules or ions. This transfer is what defines an acid or a base in the Brønsted-Lowry framework, where acids are defined primarily as proton donors and bases as proton acceptors.

When examining amphiprotic species, it's important to consider their ability to either lose or gain protons depending on the surrounding chemical environment. For instance, the bicarbonate ion ( HCO_3^- ) can donate a proton to form carbonate ( CO_3^{2-} ), or accept a proton to form carbonic acid ( H_2CO_3 ). This highlights the dynamic nature of proton transfer.

• Proton donation results in the formation of a conjugate base.
• Proton acceptance leads to the formation of a conjugate acid.

Whether a molecule acts as a proton donor or acceptor is influenced by factors such as pH levels and the presence of other reactive species. Such interactions underscore the importance of understanding the movement of protons in chemical reactions.

Conjugate Acid-Base Pairs

A crucial aspect of acid-base chemistry is the concept of conjugate acid-base pairs. This refers to the pair of molecules or ions related by the loss or gain of a single proton. Each acid has a corresponding conjugate base that forms when a proton is donated, and each base has a conjugate acid that forms upon proton acceptance.

For example, in the case of HSO_4^- :

• As it donates a proton, it forms SO_4^{2-} , its conjugate base.
• As it accepts a proton, it forms H_2SO_4 , its conjugate acid.

This pair reflects the reversible nature of acid-base reactions and emphasizes the capability of species to balance or alter their proton exchange activity according to prevailing chemical conditions.

Conjugate acid-base pairs are integral in understanding the equilibrium and direction of acid-base reactions. They also help in predicting the behavior of chemicals in various environments, thus providing key insights into a wide range of chemical and biological processes.