Question

According to the Brønsted-Lowry theory, which of the following would you expect to act as an acid? Which as a base? (a) \(\mathrm{CHO}_{2}^{-}\) (b) \(\mathrm{NH}_{4}^{+}\) (c) \(\mathrm{HSO}_{3}^{-}\)

Short answer

Question: Classify the given species as an acid or a base according to the Brønsted-Lowry theory: (a) \(\mathrm{CHO}_{2}^{-}\), (b) \(\mathrm{NH}_{4}^{+}\), (c) \(\mathrm{HSO}_{3}^{-}\). Answer: (a) \(\mathrm{CHO}_{2}^{-}\) is a base, (b) \(\mathrm{NH}_{4}^{+}\) is an acid, (c) \(\mathrm{HSO}_{3}^{-}\) is amphoteric (can act as both an acid and a base).

Step-by-step solution

(a) Identify \(\mathrm{CHO}_{2}^{-}\) as an acid or a base

We have to see if the \(\mathrm{CHO}_{2}^{-}\) can donate or accept a proton. Looking at the structure of \(\mathrm{CHO}_{2}^{-}\) (formate ion), there is an oxygen with a negative charge and a hydrogen bonded to it. Oxygen, being electronegative, can attract a proton and form a bond (O-H), giving us a molecule of formic acid (\(\mathrm{HCO}_{2}\mathrm{H}\)). Therefore, \(\mathrm{CHO}_{2}^{-}\) can act as a Brønsted-Lowry base.

(b) Identify \(\mathrm{NH}_{4}^{+}\) as an acid or a base

Now let's analyze the \(\mathrm{NH}_{4}^{+}\) ion (ammonium ion). The ammonium ion has a positive charge and already has four hydrogen atoms bonded to the nitrogen. If the \(\mathrm{NH}_{4}^{+}\) were to donate one of its hydrogen atoms as a proton, it would turn into ammonia (\(\mathrm{NH}_{3}\)) which is a neutral molecule. Therefore, \(\mathrm{NH}_{4}^{+}\) can act as a Brønsted-Lowry acid.

(c) Identify \(\mathrm{HSO}_{3}^{-}\) as an acid or a base

Lastly, let's consider the \(\mathrm{HSO}_{3}^{-}\) ion (hydrogen sulfite ion). This ion has a sulfur atom bonded to three oxygen atoms and one hydrogen atom. One of the oxygen atoms has a negative charge and a hydrogen atom bonded to it. The hydrogen atom can be donated as a proton, resulting in a sulfite ion (\(\mathrm{SO}_{3}^{2-}\)). Therefore, the \(\mathrm{HSO}_{3}^{-}\) can act as a Brønsted-Lowry acid. However, since there is also a negatively charged oxygen within the structure, the hydrogen sulfite ion can also accept a proton, resulting in a molecule of sulfurous acid (\(\mathrm{H}_{2}\mathrm{SO}_{3}\)). Thus, \(\mathrm{HSO}_{3}^{-}\) can act as both a Brønsted-Lowry acid and a base, making it an amphoteric species.

Key concepts

Understanding Acid-Base Reactions

The Brønsted-Lowry theory is a fundamental concept in chemistry for identifying acids and bases. According to this theory:

• An acid is a substance that can donate a proton (H⁺).
• A base is a substance that can accept a proton.

To determine whether a compound is an acid or a base in a reaction, you need to check its ability to donate or accept protons. This theory is versatile and works in many acid-base reactions, not just those in water.
A reaction involves the transfer of protons from an acid to a base. For example, ammonia ( NH₃ ) can accept a proton from water, acting as a base, while water donates a proton, acting as an acid. The ability to donate and accept protons under different conditions is crucial in various chemical and biological processes.

The Role of the Formate Ion

The formate ion (CHO₂^- ) plays an important role in acid-base reactions. This ion features a negatively charged oxygen which is ideal for accepting a proton. By accepting a proton, it forms formic acid ( HCO₂H ), exhibiting its nature as a base in the Brønsted-Lowry sense.
The formate ion is often involved in reactions where it behaves as a base. Its capacity to accept a proton makes it useful in neutralizing acids and in buffering systems. The characteristics of the formate ion highlight the intricacies of ion behavior in chemical reactions, especially in varying pH environments.

Understanding Ammonium Ion Behavior

The ammonium ion (NH₄⁺ ) is a well-known example of a Brønsted-Lowry acid. It is formed when ammonia ( NH₃ ) accepts a proton, and as a result, it can donate this proton in other reactions. When the ammonium ion donates a proton, it returns to ammonia, highlighting its acidic characteristic.
This behavior enables the ammonium ion to participate in various chemical reactions, notably in biological systems. It's common in tissues and biological fluids, maintaining pH levels through its ability to donate protons. Understanding this can help in grasping how pH balance is maintained in living organisms and chemical systems.

Exploring Hydrogen Sulfite Ion

The hydrogen sulfite ion (HSO₃^- ) demonstrates both acidic and basic properties, making it an amphoteric ion. It can donate a proton to become sulfite ion ( SO₃^2- ), thus acting as an acid. Alternatively, it can accept a proton to form sulfurous acid ( H₂SO₃ ), exhibiting base-like behavior.
This dual capability makes hydrogen sulfite an interesting study in chemistry, especially in environmental science where such ions play a role in natural buffering systems. Its amphoteric nature is important in processes where pH needs to be controlled within narrow limits. This ability to switch roles based on environmental conditions provides excellent insights into the dynamic nature of chemical interactions.

Definition and Properties of Amphoteric Species

Amphoteric species are compounds that can both donate and accept protons.
The hydrogen sulfite ion (HSO₃^- ) is a great example, as it can act as either an acid or a base depending on the reacting species present. This property occurs because the compound has structures that stabilize it whether it gains or loses a proton.
Amphoteric species are crucial in many biochemical and chemical processes. They offer versatility in reactions, often seen in buffering solutions where maintaining a stable pH is essential. Understanding amphoteric species provides a deeper comprehension of chemical equilibria and the balance of reactions in diverse scientific fields. This adaptability of function makes them indispensable in both natural and industrial applications.