Question

Identify the Bronsted-Lowry acid and base in each of the following neutralization reactions: (a) \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(a q)+\mathrm{LiOH}(a q) \longrightarrow \mathrm{LiC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(a q)+\mathrm{H}_{2} \mathrm{O}(l)\) (b) \(2 \mathrm{NH}_{3}(a q)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \longrightarrow\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}(a q)\)

Short answer

(a) Acid: \(\mathrm{HC}_2\mathrm{H}_3\mathrm{O}_2\), Base: \(\mathrm{LiOH}\). (b) Acid: \(\mathrm{H}_2\mathrm{SO}_4\), Base: \(\mathrm{NH}_3\).

Step-by-step solution

Understanding Bronsted-Lowry Theory

The Bronsted-Lowry theory defines acids and bases as follows: An acid is a substance that donates a proton (H⁺), while a base is a substance that accepts a proton.

Identify Acid and Base in Reaction (a)

In reaction (a), acetic acid, \(\mathrm{HC}_2\mathrm{H}_3\mathrm{O}_2\), donates a proton to become acetate \(\mathrm{C}_2\mathrm{H}_3\mathrm{O}_2^-\), thus acting as the acid. Lithium hydroxide, \(\mathrm{LiOH}\), provides a hydroxide ion, which accepts the proton to form water, thus acting as the base.

Identify Acid and Base in Reaction (b)

In reaction (b), \(\mathrm{H}_2\mathrm{SO}_4\) donates protons to form two \(\mathrm{NH}_4^+\) ions, which indicates that it is the acid. \(\mathrm{NH}_3\) accepts the protons to form \(\mathrm{NH}_4^+\), making it the base.

Key concepts

Neutralization Reactions

When we talk about neutralization reactions, we're discussing a special type of chemical reaction between an acid and a base. This reaction typically results in the formation of a salt and water. In Bronsted-Lowry terms, a neutralization occurs when the acid donates a proton (hydrogen ion) to the base.
In many everyday scenarios, such as the use of antacids or making soap, we observe these reactions.

• Antacids neutralize excess stomach acid, providing relief from discomfort.
• Soap is made from fats and alkalis (a type of base) reacting to form soap and glycerin, through a process called saponification, which is essentially a neutralization reaction.
• Even some natural processes like soil pH adjustments involve neutralization.

In our exercise, the first reaction is between acetic acid and lithium hydroxide, and the second is between sulfuric acid and ammonia. Both reactions exemplify how a base neutralizes an acid to create a more stable, less reactive end product, echoing the everyday utility of these reactions.

Proton Donor and Acceptor

The Bronsted-Lowry concept of acids and bases focuses on the transfer of protons (H⁺ ions) between substances. In this framework:

• An acid is known as a proton donor.
• A base is known as a proton acceptor.

It's a simple concept, but it's fundamental to understanding how many reactions occur in chemistry.
Let's break it down with the examples from the exercise:
In reaction (a), acetic acid (HC₂H₃O₂) acts as the proton donor. It gives away a proton to form acetate (C₂H₃O₂⁻). This is what makes it an acid in this context. Lithium hydroxide (LiOH), the base, accepts the proton to form water (H₂O).
In reaction (b), sulfuric acid (H₂SO₄) donates protons, forming ammonium ions (NH₄⁺) when ammonia (NH₃) accepts them. This process highlights the dynamic role of proton transfer in chemical reactions, with donor and acceptor repeatedly swapping roles as acids and bases.

Chemical Reactions

Chemical reactions are processes where substances (reactants) convert into new substances (products). Studying these reactions helps us understand changes in energy, the composition of materials, and the transformations they undergo.
The Bronsted-Lowry neutralization reactions are just a subset of these chemical reactions that specifically involve acids and bases exchanging protons.

• Reaction (a) transforms acetic acid and lithium hydroxide into water and lithium acetate, showcasing a quintessential neutralization process.
• Reaction (b) sees sulfuric acid reacting with ammonia to produce ammonium sulfate, demonstrating a multi-step proton exchange.

Understanding these reactions is crucial for fields ranging from environmental science, where monitored reactions impact ecosystem health, to biochemistry, where such exchanges are integral to cellular processes.
Furthermore, recognizing the role of proton exchange helps chemists develop new materials and pharmaceuticals, advance scientific theories, and improve industrial processes. It's not just about mixing things together—it's about unveiling the invisible forces and interactions that define our physical world.