Question

Which of the following are amphoteric species? (a) \(\mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{HSO}_{3}^{-}\) (c) \(\mathrm{SO}_{4}^{2-}\)

Short answer

\(\mathrm{H}_{2} \mathrm{O}\) and \(\mathrm{HSO}_{3}^{-}\) are amphoteric species, whereas \(\mathrm{SO}_{4}^{2-}\) is not.

Step-by-step solution

Analyze \(H_2O\)

Water (\(H_2O\)) has both hydrogen atoms for donating and lone pairs of electrons on the oxygen atom for accepting protons, allowing it to act as both, an acid and a base. Therefore, \(H_2O\) is an amphoteric species.

Analyze \(\mathrm{HSO}_{3}^{-}\)

\(\mathrm{HSO}_{3}^{-}\) has a hydrogen atom that it can donate, thereby behaving as an acid. Moreover, it has lone pairs of electrons on oxygen that can accept protons, showing its behavior as a base. Therefore, \(\mathrm{HSO}_{3}^{-}\) is also an amphoteric species.

Analyze \(\mathrm{SO}_{4}^{2-}\)

\(\mathrm{SO}_{4}^{2-}\) does not have any hydrogen atoms that it can donate, which means it cannot behave as an acid. It has only lone pairs on the oxygen atom which can accept protons, and thus acts only as a base. Therefore, \(\mathrm{SO}_{4}^{2-}\) is not an amphoteric species.

Key concepts

Acid-Base Chemistry

In the realm of acid-base chemistry, understanding how substances interact is essential. Acids are known to donate protons ( H^+ ), while bases accept them. This dynamic gives rise to the concept of amphoteric species. Amphoteric species can act as both acids and bases, depending on their environment. For example:

• Acids: Compounds like HCl donate a proton to H_2O in a reaction, generating Cl^− and H_3O^+ (hydronium ion).
• Bases: On the flip side, compounds like NH_3 accept protons, generating NH_4^+ (ammonium ion).

When we talk about amphoteric substances such as water ( H_2O ), they have the potential to switch roles. In one scenario, they may donate a proton, acting as an acid. In another, they may accept a proton, showcasing their basic behavior. This dual capability makes them versatile in chemical reactions. Amphoteric behavior is crucial in biochemical processes, industrial applications, and the environment.

Proton Donor and Acceptor

The concept of protons in chemistry is fundamental, especially when analyzing proton donor and acceptor scenarios. To understand if a species can donate or accept protons, it is vital to look at its chemical structure.

• Proton Donors: These are chemical species that have hydrogen atoms bonded in a manner that can easily break away, releasing a H^+ ion into the solution. For example, HSO_3^− can donate a proton, thus behaving like an acid.
• Proton Acceptors: On the other hand, bases often have lone pairs of electrons ideally placed to capture a proton. Water is a typical proton acceptor when it reacts with acids, using its lone pairs on the oxygen atom to bond with H^+ and create H_3O^+ .

The interplay between proton donor and acceptor is central to understanding many chemical reactions. It helps determine the role a molecule will play in a reaction and is foundational to acid-base chemistry theories.

Chemical Species Analysis

When analyzing chemical species to determine whether they are amphoteric, it's essential to closely look at their atomic composition and structural characteristics.

• Hydrogen Atoms: The presence of hydrogen atoms is a cue that a substance might be capable of donating protons, which is essential for amphoteric behavior. For instance, water ( H_2O ) and hydrogen sulfate ( HSO_3^− ) possess hydrogen atoms allowing them to act as acids.
• Lone Pairs of Electrons: Check if the molecule has lone pairs of electrons, which often means it can accept protons, showing potential to act as a base. H_2O and HSO_3^− also have this quality owing to the lone pairs on their oxygen atoms.
• Ionic State: The overall charge on a molecule can influence its ability to gain or lose protons. SO_4^{2-} , for example, lacks hydrogen and primarily accepts protons owing to its electron-rich oxygen atoms, making it a base rather than amphoteric.

By keenly examining these features, one can predict the behavior of chemical species in various reactions, determining whether they exhibit amphoteric properties or serve strictly as acids or bases.