Problem 4 - Analytical Chemistry

Question

Write the ionization reaction of aniline, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\), in glacial acetic acid, and identify the conjugate acid of aniline. Write the ionization reaction of phenol, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH}\), in ethylene diamine, \(\mathrm{NH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2},\) and identify the conjugate base of phenol.

Step-by-Step Solution

Answer

The conjugate acid of aniline is \\(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{3}^{+}\\), and the conjugate base of phenol is \\(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{O}^{-}\\).

Step 1: Understanding Ionization of Aniline in Glacial Acetic Acid

In glacial acetic acid, aniline, \(\mathrm{C}_{6} \mathrm{H}_{5}\mathrm{NH}_{2}\), will act as a base and accept a proton (H+) from the glacial acetic acid, a proton donor, to form its conjugate acid and acetate ions. The reaction is shown as follows:\[ \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2} + \mathrm{CH}_{3}\mathrm{COOH} \rightarrow \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{3}^{+} + \mathrm{CH}_{3}\mathrm{COO}^{-} \]In this reaction, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{3}^{+}\) is the conjugate acid of aniline.

Step 2: Understanding Ionization of Phenol in Ethylene Diamine

In ethylene diamine, which is a strong base, phenol, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH}\), will donate a proton to ethylene diamine, forming a phenoxide ion and an ethylene diammonium ion. The reaction proceeds as follows:\[ \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH} + \mathrm{NH}_{2}\mathrm{CH}_{2}\mathrm{CH}_{2}\mathrm{NH}_{2} \rightarrow \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{O}^{-} + \mathrm{NH}_{3}\mathrm{CH}_{2}\mathrm{CH}_{2}\mathrm{NH}_{3}^{+} \]In this reaction, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{O}^{-}\) is the conjugate base of phenol.

Key Concepts

Acid-Base Reactions

Acid-base reactions are a fundamental part of chemistry that involve the transfer of protons, or hydrogen ions ( +) between chemical species. In these reactions, acids donate protons while bases accept them. This interaction leads to the formation of new substances, typically a conjugate acid-base pair.
In the ionization of aniline in glacial acetic acid, aniline serves as the base. It accepts a proton from the acetic acid (the acid), forming aniline's conjugate acid ( _{3}^{+} ). Meanwhile, acetic acid loses a proton, transforming into its conjugate base, acetate ( _{3} ^{-}).
Similarly, in the case of phenol reacting in ethylene diamine, phenol acts as the acid and transfers a proton to the base, ethylene diamine. This exchange creates the phenoxide ion, which is the conjugate base of phenol, and the ethylene diammonium ion as the new product of the base.

• Acids: Proton donors like acetic acid and phenol.
• Bases: Proton acceptors including aniline and ethylene diamine.
• Ions Produced: Acetate ions, phenoxide ions, and ethylene diammonium ions.

Conjugate Acids and Bases

Conjugate acids and bases are pairs of molecules or ions that differ by exactly one proton. When an acid donates a proton, it becomes its conjugate base. Conversely, when a base gains a proton, it becomes its conjugate acid.
In the ionization of aniline, the molecule's acceptance of a proton from acetic acid turns it into _{3}^{+} , representing the conjugate acid of aniline. On the other hand, acetate ( _{3} ^{-}) is the conjugate base of acetic acid after it gives away its proton.
For phenol, after donating a proton to ethylene diamine, it becomes _{5} ^{-}, its conjugate base. Meanwhile, ethylene diamine becomes its conjugate acid after receiving a proton from phenol, transforming into []_{3} _{3}^{+} .
These proton exchanges are essential in understanding the behavior of chemical reactions and predicting the products formed.

• Conjugate Acid: Aniline becomes _{3}^{+} when it gains a proton.
• Conjugate Base: Phenol becomes _{5} ^{-} when it loses a proton.
• Reaction Balance: Conjugate pairs help maintain the equilibrium of reactions.

Organic Chemistry

Organic chemistry focuses on molecules primarily made of carbon and hydrogen, often incorporating other elements such as oxygen, nitrogen, sulfur, and phosphorus. Understanding organic reactions, like ionization and acid-base reactions, is crucial in organic chemistry.
Aniline ( _{2} ) and phenol ( _{5} ) are both organic compounds with functional groups influencing their chemical behavior. Aniline has an amino group ( _{2} ), enabling it to accept a proton in acid-base reactions. Phenol, with a hydroxyl group ( ext{o}_{h} ), can donate a proton, highlighting its weak acidic properties.
Ethylene diamine ( _{2}_{2}_{2} ) plays a role as a strong base in reactions involving proton transfers, while glacial acetic acid ( _{3} ) is an important weak organic acid. These characteristics make it possible to predict and understand their role in chemical reactions, demonstrating the importance of identifying functional groups in organic chemistry.

• Functional Groups: Determine the reactivity of organic molecules like aniline and phenol.
• Proton Transfer Ability: Differentiates acids and bases, contributing to their roles in reaction mechanisms.
• Versatility: Organic acid-base chemistry underpins numerous biological and industrial processes.