Problem 61 - General Chemistry: Principles and Modern Applications

Question

Write the formulas of the products expected to form in the following situations. If no reaction occurs, write N.R. (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2}(\mathrm{aq})+\mathrm{HCl}(\mathrm{aq}) \longrightarrow\) (b) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{N}(\mathrm{aq})+\mathrm{HBr}(\mathrm{aq}) \longrightarrow\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{3}^{+}(\mathrm{aq})+\mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq}) \longrightarrow\) (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{3}^{+}(\mathrm{aq})+\mathrm{OH}^{-}(\mathrm{aq}) \longrightarrow\)

Step-by-Step Solution

Answer

\(a) CH3CH2NH3^+ + Cl^- \) \(b) (CH3)3NH^+ + Br^- \) \(c) No reaction \) \(d) CH3CH2NH2 + H2O \)

Step 1 - Reaction of Amine with Aqueous Acid

First we look at the reaction of the amine group with the aqueous solution of hydrochloric acid. Here, the nitrogen atom in the ethylamine (CH3CH2NH2) donates an electron pair to form a bond with a proton (H+) from the hydrochloric acid (HCl). This leads to formation of an ethylammonium ion (CH3CH2NH3+) and chloride ion (Cl-) as the products.

Step 2 - Reaction of tri-methyl-amine with Aqueous Acid

For the reaction between trimethylamine ((CH3)3N) and hydrobromic acid (HBr), a similar process happens. The nitrogen atom in the trimethylamine accepts a proton (H+) from the hydrobromic acid to form trimethylammonium ion ((CH3)3NH+) and bromide ion (Br−).

Step 3 - Interaction with Hydronium Ions

On basis of our understanding of acid–base reactions, the CH3CH2NH3+ and H3O+ don’t react because they are both ions formed from acids. Therefore, we conclude there is 'No Reaction' happening in this case.

Step 4 - Reaction with Hydroxide Ions

With the reaction between CH3CH2NH3+ and OH-, the hydroxide ions (OH−) from water strip off the H+ ion originally added by the acid from the ammonium ion changing it back to the original amine CH3CH2NH2. Thus we get ethylamine and water (H2O) as products.

Key Concepts

Amine Chemistry

Amines are fascinating organic compounds that play vital roles in chemistry. They are derivatives of ammonia where one or more hydrogen atoms have been replaced by alkyl or aryl groups. This ability to form different structural variations gives amines unique chemical properties.
The nitrogen atom in amines has a lone pair of electrons, making it a base. This basicity is central to understanding how amines interact in chemical reactions. Amines can donate this lone pair to accept protons from acids, forming an alkyl ammonium ion. This property is demonstrated in reactions like those with hydrochloric acid and hydrobromic acid where the nitrogen atom forms a bond with the available proton.
This characteristic is crucial in both organic synthesis and biological systems where amines act as key building blocks.

Ionic Reactions

Ionic reactions involve the formation or breaking of ions in solution. When an amine reacts with an acid, like hydrochloric acid or hydrobromic acid, an ionic reaction takes place. These types of reactions are crucial as they occur through the exchange of protons and electrons between species.
The ionic nature of these reactions can be illustrated by the formation of ammonium ions (e.g., CH3CH2NH3+ and (CH3)3NH+) and halide ions (e.g., Cl- and Br-) in the solutions. These reactions are reversible, aligning with the basics of acid-base chemistry where equilibrium can be achieved.
Understanding ionic reactions is vital for predicting how substances can change in aqueous environments, which is often encountered in laboratory and industrial applications.

Organic Chemistry

Organic chemistry revolves around carbon-containing compounds, among which amines are a significant class. Recognizing the structural patterns and understanding their chemical behavior forms the foundation of studying organic chemistry. Reactions involving organic compounds are often associated with changes in structure and bonding.
Amines, due to their basic nature, participate actively in organic reactions, often involving proton transfer processes. The exchange of protons in solutions of amines and acids illustrates how organic reactions can transform molecular structures, resulting in new products.
These transformations highlight the dynamic nature of organic molecules and form the basis of synthesizing wider varieties of chemical compounds necessary for the advancement in fields like pharmacology and materials science.

Equilibrium Reactions

Equilibrium reactions are fundamental in chemistry, especially involving weak bases like amines. These reactions do not go to completion but instead reach a state where both reactants and products are present in a steady ratio. This balance reflects the dynamic aspect of chemical processes.
In the case of amines reacting with acids, such as hydrochloric acid, an equilibrium can be achieved between the ammonium ion and the original amine. Similarly, reactions involving hydroxide ions with ammonium ions can also illustrate equilibrium concepts, as they affect the extent to which amines revert to their original state or remain ionized.
Grasping the concept of chemical equilibrium is vital for designing reactions and predicting product formation. It's a cornerstone for advancements in chemical engineering and the development of new chemical processes.