Question

When hydrogen chloride dissolves in water, the product is "hydrochloric acid." Such a solution contains water, \(\mathrm{H}_{3} \mathrm{O} \oplus\), and \(\mathrm{Cl}^{(-)}\). Which of these species are Lewis acids? Lewis bases? If you have more than one compound per category, arrange them in order of decreasing strength.

Short answer

In the given species, the Lewis acid is \(\mathrm{H}_{3} \mathrm{O} \oplus\) (strongest), and the Lewis bases are \(\mathrm{Cl}^{(-)}\) (strongest) and Water (weaker).

Step-by-step solution

Lewis Acids and Bases Definitions

A Lewis acid is a substance that can accept an electron pair, while a Lewis base is a substance that can donate an electron pair. In short, Lewis acids are electron pair acceptors, and Lewis bases are electron pair donors.

Identify the Lewis Acids and Bases

Now let's look at the species and identify them as Lewis acids or bases: 1. Water: Water has two lone pairs of electrons and can donate an electron pair, making it a Lewis base. 2. \(\mathrm{H}_{3} \mathrm{O} \oplus\): The hydronium ion lacks an electron pair, so it can accept an electron pair. Therefore, it is a Lewis acid. 3. \(\mathrm{Cl}^{(-)}\): Cloride ion has three lone pairs of electrons, enabling it to donate an electron pair. Hence, it is a Lewis base.

Determine the order of Decreasing Strength

1. Strongest Lewis acid: \(\mathrm{H}_{3} \mathrm{O} \oplus\) (it is the only Lewis acid among the species we analyzed). 2. Strongest to Weakest Lewis bases: \(\mathrm{Cl}^{(-)}\) and Water. Comparing their basicity, we find that \(\mathrm{Cl}^{(-)}\) has a stronger tendency to donate an electron pair, due to its negative charge, which makes it stronger than water.

Summary

The Lewis acids and bases among the given species are: - Lewis acid: \(\mathrm{H}_{3} \mathrm{O} \oplus\) (strongest) - Lewis bases (from strongest to weakest): \(\mathrm{Cl}^{(-)}\) and Water

Key concepts

Hydrochloric Acid Solution

When discussing hydrochloric acid (HCl) within the framework of Lewis acid-base theory, it's essential to start by understanding what happens when hydrogen chloride gas dissolves in water. This dissolution process results in the creation of a hydrochloric acid solution, which is a common and strong acid used in various chemical processes.

Formation of Acids and Bases

Upon dissolution, hydrogen chloride reacts with water to produce hydronium ions ()}) and chloride ions ()}). During this process, water acts as a Lewis base, donating an electron pair to form the hydronium ion. Conversely, the hydronium ion is a product that can act as a Lewis acid in other reactions. Let's break this down:

• The hydrogen chloride initially acts as a Lewis acid, accepting an electron pair from water.
• Upon forming the hydrochloric acid solution, hydronium ions and chloride ions are present in the mixture.
• The formation of hydronium is crucial, as it represents the acidic nature of the solution while chloride represents the basic contribution, as we'll discuss further in the chloride ion section.

It's noteworthy that the acid-base interaction in creating hydrochloric acid solutions embodies the concept of Lewis acid-base reactions where electron pair transfers dictate reactivity.

Hydronium Ion

The hydronium ion ()}), often represented with the chemical formula )}), plays a central role in the dissociation of acids in water.

Role as a Lewis Acid

The hydronium ion is considered a Lewis acid because it is capable of accepting an electron pair. In the dissolution of hydrogen chloride to form hydrochloric acid, the formation of the hydronium ion is a pivotal step in illustrating the chemical's acidic properties. The electron-deficient nature of the proton in the hydronium ion makes it eager for electron pairs, thus making it a potent Lewis acid.

• Its formation can be seen as the hallmark of the acidification process in water.
• Understanding the hydronium ion's behavior is essential to grasp the concept of pH and the strength of acids and bases.
• The propensity of )} to act as an electron pair acceptor stems from its positive charge, which effectively pulls electron density towards itself.

The hydronium ion is not only a key player in the acid-base reactions within hydrochloric acid solutions but in all aqueous acid-base chemistry.

Chloride Ion as Lewis Base

In contrast to the hydronium ion, the chloride ion ()}) is classified as a Lewis base. After Hydrogen chloride gas dissolves in water, the chloride ion is the other resultant species alongside the hydronium ion.

Electron Pair Donor

As a Lewis base, the chloride ion possesses three lone pairs of electrons on its chlorine atom, which are available for donation to electron-pair-accepting species, known as Lewis acids. This ability to donate electron pairs makes it an important base in many chemical reactions:

• It is a byproduct of the formation of hydrochloric acid in water.
• Given its negative charge, it has a high electron density, increasing its tendency to donate electrons compared to neutral molecules like water.
• In comparison to water, which can also act as a Lewis base, the chloride ion is stronger due to its full negative charge and readily available lone pairs.

Understanding the role of the chloride ion as a Lewis base in the context of hydrochloric acid solutions helps encapsulate the nuanced interplay of acids and bases in chemical solutions.