Problem 3 - Chemistry: Principles and Reactions

Question

According to the Bronsted-Lowry theory, which of the following would you expect to act as an acid? Which as a base? (a) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NH}_{3}{\underline{\phantom{xx}}}^{+}\) (b) \(\mathrm{HClO}\) (c) \(\mathrm{CN}^{-}\)

Step-by-Step Solution

Answer

Question: Identify the role of each substance as an acid or a base according to the Bronsted-Lowry theory: a) \(\mathrm{C}_{2}\mathrm{H}_{5}\mathrm{NH}_{3}{\underline{\phantom{xx}}}^{+}\) b) \(\mathrm{HClO}\) c) \(\mathrm{CN}^{-}\) Answer: a) \(\mathrm{C}_{2}\mathrm{H}_{5}\mathrm{NH}_{3}{\underline{\phantom{xx}}}^{+}\) acts as an acid. b) \(\mathrm{HClO}\) acts as an acid. c) \(\mathrm{CN}^{-}\) acts as a base.

Step 1: (Identifying Acid or Base for \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NH}_{3}{ }^{+}\))

To analyze whether \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NH}_{3}{\underline{\phantom{xx}}}^{+}\) is an acid or a base, take note of the positive charge on the nitrogen atom. This means that it has an extra proton (H+), which it can potentially donate. Therefore, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NH}_{3}{\underline{\phantom{xx}}}^{+}\) will act as an acid.

Step 2: (Identifying Acid or Base for \(\mathrm{HClO}\))

In the case of \(\mathrm{HClO}\), notice that it contains an acidic hydrogen (H+) bonded to an oxygen atom (O), which is known to be electronegative. This feature makes it easy to dissociate and donate a proton. As a result, \(\mathrm{HClO}\) will act as an acid.

Step 3: (Identifying Acid or Base for \(\mathrm{CN}^{-}\))

Considering the negatively charged \(\mathrm{CN}^{-}\), it has an electron pair on the carbon atom, making it capable of accepting a proton (H+). Consequently, \(\mathrm{CN}^{-}\) will act as a base according to the Bronsted-Lowry theory.

Key Concepts

Acid-Base Reactions

At the heart of the Bronsted-Lowry theory are acid-base reactions. These reactions are a fundamental part of chemistry and can be observed in everyday life. But what exactly are they? In simple terms, an acid-base reaction is a process where an acid donates a proton to a base. This idea forms the basis of understanding how acids and bases interact. When identifying whether a substance will act as an acid or a base in a reaction:

• An acid is a substance that can donate a proton, which is a hydrogen ion (H\(^+\)).
• A base, on the other hand, is a substance that can accept a proton.

Understanding this exchange process is crucial to predicting how different chemicals will behave in reactions, especially when it comes to determining acidity or basicity in compounds.

Proton Donation

Proton donation is a key aspect of the behavior of acids. An acid's ability to donate protons defines its role in a chemical reaction. In the Bronsted-Lowry theory, proton donation happens when an acid loses its hydrogen ion, forming its conjugate base. For example:

• The compound \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NH}_{3}^{+}\) contains an extra proton which it can donate, thus behaving as an acid in a reaction.
• Similarly, \(\mathrm{HClO}\) can donate its acidic hydrogen to form \(\mathrm{ClO}^{-}\), also marking it as an acid.

Proton donation results in a shift towards a more neutral charge balance within the reacting species. Recognizing this action helps in determining the strength and role of an acid in any given reaction.

Electronegative Elements

Electronegative elements play a significant role in the behavior and reactivity of acids. Elements like oxygen and nitrogen have a strong tendency to attract electrons towards themselves. This property is relevant because:

• It enables the formation of bonds with hydrogen that are more easily broken, facilitating the release of protons necessary for acid function.
• In acids like \(\mathrm{HClO}\), the presence of oxygen makes it easier for the compound to release its hydrogen ion and thus act as an acid during chemical reactions.

Understanding electronegativity helps predict the strength of acids and their tendency to release protons, shaping the outcomes of chemical reactions.

Dissociation of Acids

Dissociation is the process where an acid breaks apart to release ions, specifically hydrogen ions or protons. This process is central to the function of acids based on the Bronsted-Lowry theory. Key features of acid dissociation include:

• In compounds like \(\mathrm{HClO}\), the dissociation involves separating the \(H^+\) ion from the rest of the molecule, \(\mathrm{ClO}^{-}\).
• This release of \(H^+\) ions into a solution is what gives acids their characteristic properties, such as pH and reactivity.

The efficiency of an acid to dissociate depends heavily on its structure and the presence of electronegative elements which aid in weakening the \(H^+\) bond. Mastering this concept is crucial for predicting how an acid will behave in different chemical environments.