Question

\(\mathrm{NH}_{3}(g)\) and \(\mathrm{HCl}(g)\) react to form the ionic solid \(\mathrm{NH}_{4} \mathrm{Cl}(s) .\) Which substance is the Brønsted-Lowry acid in this reaction? Which is the Brønsted-Lowry base?

Short answer

In the reaction \(\mathrm{NH}_3(g) + \mathrm{HCl}(g) \rightarrow \mathrm{NH}_4\mathrm{Cl}(s)\), the Brønsted-Lowry acid is hydrogen chloride (HCl), which donates a proton, and the Brønsted-Lowry base is ammonia (NH₃), which accepts a proton.

Step-by-step solution

Recall the definitions of Brønsted-Lowry acids and bases

A Brønsted-Lowry acid is a substance that donates a proton, or hydrogen ion (H⁺), to another substance. A Brønsted-Lowry base, on the other hand, is a substance that accepts a proton, or hydrogen ion (H⁺), from another substance.

Write down the given reaction

The given reaction is: \[\mathrm{NH}_3(g) + \mathrm{HCl}(g) \rightarrow \mathrm{NH}_4\mathrm{Cl}(s)\]

Identify the proton donor (Acid) and proton acceptor (Base)

In the given reaction, ammonia (NH₃) has a lone pair of electrons, which allows it to accept a hydrogen ion (proton) from hydrogen chloride (HCl). As the proton donor, hydrogen chloride (HCl) is the Brønsted-Lowry acid. Ammonia (NH₃), which accepts the proton from HCl, is the Brønsted-Lowry base. After accepting the proton, NH₃ becomes NH₄⁺, which then combines with Cl⁻ to form the ionic compound ammonium chloride (NH₄Cl).

State the Brønsted-Lowry acid and base for this reaction

In the reaction between ammonia (NH₃) and hydrogen chloride (HCl) gases to form the ionic solid ammonium chloride (NH₄Cl), the Brønsted-Lowry acid is hydrogen chloride (HCl) and the Brønsted-Lowry base is ammonia (NH₃).

Key concepts

Acid-Base Reactions

Acid-base reactions are fundamental chemical processes where acids and bases interact, often resulting in the formation of water and a salt. In this type of reaction, an acid donates a proton (H⁺) to a base, which accepts the proton. This process can occur in various states—gases, liquids, or solids. The reaction between ammonia (NH₃) and hydrogen chloride (HCl) is a classic example. When these gases combine, a proton transfer takes place, leading to the formation of the solid ammonium chloride (NH₄Cl).
This simple proton exchange highlights the versatility of acid-base reactions beyond liquid solutions, showcasing their presence in gaseous states as well. Such interactions are vital in understanding chemical behavior in different environments.
Understanding acid-base reactions allows chemists to manipulate chemical processes, predict reaction outcomes, and synthesize desired compounds effectively.

Proton Donor

In the Brønsted-Lowry theory of acids and bases, an acid is known as a proton donor. This means that during a reaction, the acid relinquishes a hydrogen ion (H⁺) to another substance. Proton donation is crucial in the identification of acids in chemical reactions.
For instance, in the reaction between NH₃ and HCl, hydrogen chloride (HCl) serves as the proton donor. It gives up its proton to NH₃, leading to the formation of NH₄⁺, the ammonium ion. This ability to release a proton is what classifies HCl as a Brønsted-Lowry acid.
Understanding proton donors in reactions helps in determining how substances interact and transform, providing insight into the nature and structure of the resulting compounds.

Proton Acceptor

The concept of a proton acceptor is central to the Brønsted-Lowry definition of bases. A base is a substance that receives a proton (H⁺) from an acid. Proton acceptance enables the identification and classification of bases in numerous chemical reactions.
In the interaction between ammonia (NH₃) and hydrogen chloride (HCl), NH₃ acts as the proton acceptor. By accepting a proton from HCl, NH₃ transforms into the ammonium ion (NH₄⁺). This process underscores NH₃'s role as the Brønsted-Lowry base in this reaction.
Identifying proton acceptors is essential in understanding reaction mechanisms, as it highlights how molecules adjust their structures and bonding characteristics during chemical interactions.

Ionic Compounds

Ionic compounds consist of positively and negatively charged ions held together by electrostatic forces, known as ionic bonds. These compounds often form from reactions between elements or compounds that transfer electrons to achieve stability.
In the case of the reaction between NH₃ and HCl, the resulting compound is ammonium chloride (NH₄Cl). Here, NH₄⁺ (ammonium ion) and Cl⁻ (chloride ion) combine to form the solid ionic compound.
The properties of ionic compounds, such as high melting and boiling points, conductivity when molten or dissolved in water, and distinctive crystalline structures, are directly linked to their ionic bonds. Understanding ionic compounds is pivotal in fields such as material science and industrial chemistry, where they are used in various applications, from salt production to electrolyte solutions.