Question

Complete the following equation for the reaction of an amine with hydrochloric acid. $$ \left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{2} \mathrm{NH}+\mathrm{HCl}(a q) \longrightarrow $$

Short answer

The completed equation for the reaction of amine with hydrochloric acid is: \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{2} \mathrm{NH} + \mathrm{HCl} \longrightarrow \left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{2} \mathrm{NH}_{2} \mathrm{Cl}\)

Step-by-step solution

Identify the acid and the base in the reaction

The acid and base in the reaction are \(\mathrm{HCl}\) (Hydrochloric acid) and \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{2} \mathrm{NH}\) (Amine) respectively. Hydrochloric acid is a strong acid that completely dissociates in water to form \(\mathrm{H}^{+}\) and \(\mathrm{Cl}^{-}\) ions, and the amine is a weak base that accepts the proton (\(\mathrm{H}^{+}\)) from the acid.

Perform the acid-base reaction

The reaction between the acid and the base can be represented as follows: \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{2} \mathrm{NH} + \mathrm{H}^{+} \longrightarrow \left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{2} \mathrm{NH}^{+}\). The amine absorbs the hydrogen ion from the Hydrochloric acid, forming an ammonium ion.

Form the ammonium salt

The chloride ion \(\mathrm{Cl}^{-}\) from the \(\mathrm{HCl}\) then combines with the ammonium ion formed in the previous step to form the ammonium salt. The final balanced equation is therefore: \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{2} \mathrm{NH} + \mathrm{HCl} \longrightarrow \left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{2} \mathrm{NH}_{2} \mathrm{Cl}\).

Key concepts

Acid-Base Chemistry

In the realm of chemistry, the base concept of acids and bases is crucial for understanding a plethora of reactions. An acid is a substance that can donate a proton (H⁺), and a base is a substance that can accept a proton. This fundamental idea is known as the 'Bronsted-Lowry' acid–base theory.

The strength of an acid or a base is determined by its ability to donate or accept protons. Strong acids, like hydrochloric acid (HCl), dissociate completely in water to release H⁺ ions, while weak acids do not dissociate completely. On the other end, bases such as amines, have lone pairs of electrons that can readily accept H⁺ ions, with weaker bases being less inclined to do so.

Moreover, the concept of conjugate acids and bases is essential. When an acid donates a proton, it becomes a conjugate base; when a base accepts a proton, it turns into a conjugate acid. This shows that acid-base reactions are essentially 'proton transfer' processes, contributing to the formation of new substances in the chemical equilibrium of a solution.

Chemical Reactions

Chemical reactions are processes wherein substances, known as reactants, transform into new substances called products. The conservation of mass dictates that the number of atoms for each element must remain constant throughout the reaction, which leads us to the importance of balanced chemical equations.

A balanced chemical equation ensures that the law of conservation of mass is satisfied. In the reaction between an amine and hydrochloric acid, the amine functions as a base, accepting a proton from hydrochloric acid and forming an intermediate known as an ammonium ion. The ammonium ion then pairs with the leftover chloride ion, leading us to the end product of the reaction, which is an ammonium salt. The balancing of the equation is confirmed by comparing the number of atoms of each element on both sides, ensuring that they are equal. This visualization of conservation aids in understanding what occurs during the reaction at a molecular level.

Furthermore, in a chemical reaction like the one in this exercise, the acidity or basicity of the medium, catalysts, temperature, concentration of reactants, and other factors can all influence the rate and direction in which the reaction proceeds.

Ammonium Salts Formation

The formation of ammonium salts is an exemplary process demonstrating a neutralization reaction, where an acid reacts with a base to form a salt and, often, water. However, in our case with amines, no water is produced; rather, we simply get the salt known as an ammonium salt.

An ammonium salt is composed of an ammonium cation (NH₄⁺) and a negative ion or anion. In the provided exercise, the amine grabs a proton from the hydrochloric acid to form an ammonium ion. The negatively charged chloride ion (Cl^-) that remains then associates with the newly formed ammonium ion to produce an ammonium chloride salt (NH₄Cl).

These salts are versatile compounds with diverse uses, ranging from fertilizers to drugs, and are typically soluble in water. The ionic bond between the cation and anion in ammonium salts is a key feature influencing their solubility and other properties. Understanding the reaction that leads to their formation allows students to predict the products of similar reactions involving other acids and amines, a valuable skill in the chemistry discipline.