Question

According to the Bronsted-Lowry definition of acids and bases, what is a conjugate acid-base pair? Provide an example.

Short answer

A conjugate acid-base pair consists of two species that can transform into each other by the loss or gain of a proton. For instance, the acetic acid/acetate ion (CH3COOH/CH3COO-) is a conjugate acid-base pair.

Step-by-step solution

Understanding the Bronsted-Lowry Model

The first step is to understand that according to the Bronsted-Lowry model, an acid is a substance capable of donating a proton (hydrogen ion, H+), and a base is a substance capable of accepting a proton.

Identifying Conjugate Acid-Base Pair

A conjugate acid-base pair is made up of two species that transform into each other by the gain or loss of a proton. The species that donates the proton becomes the conjugate base, and the species that accepts the proton becomes the conjugate acid.

Providing an Example

An example of a conjugate acid-base pair is the pair formed by acetic acid (CH3COOH) and acetate ion (CH3COO-). Acetic acid donates a proton to become acetate ion, which can accept a proton, thus forming the conjugate acid-base pair, CH3COOH/CH3COO-.

Key concepts

Conjugate Acid-Base Pair

In the dance of acids and bases, the concept of a conjugate acid-base pair is crucial to understanding how these substances interact with each other. You can think of it as two dance partners, where one gives away a token—an H⁺ ion—and the other accepts it. To further clarify, whenever an acid releases a proton, it turns into a base—this new form is what we call the conjugate base. Conversely, when a base receives a proton, it becomes an acid—termed a conjugate acid. They are forever linked, as one cannot exist without the other’s transformation.

Here's a simple way to remember it: the acid and its corresponding conjugate base differ by one proton. Whenever you see a pair of substances that are the same except for an extra H⁺, you have spotted a conjugate acid-base pair. This understanding not only simplifies identifying these pairs but also unravels the complex network of chemical reactions they are involved in.

Proton Donation and Acceptance

The Bronsted-Lowry theory hinges on a single, pivotal encounter—the transfer of a proton, otherwise known as a hydrogen ion, symbolized by H⁺. This is a key event in the acid-base reaction, where proton donation and proton acceptance occur. Think of an acid as someone with an H⁺ to spare—it’s generous and ready to donate. Bases, on the other hand, are ready to welcome an H⁺.

Protons don't exist on their own in a solution, they are always bound to other atoms or molecules. When an acid donates a proton, it latches onto a base, thereby transforming the base into a conjugate acid. This interplay is the core of acid-base chemistry, and it's a reversible process; the roles can switch when the conditions are right, leading to a dynamic equilibrium in many solutions.

Acid-Base Reaction Examples

To truly grasp these concepts, let's dive into some common scenarios that illustrate acid-base chemistry at work. One well-known example is the reaction between hydrochloric acid (HCl) and water (H₂O). In this interaction, HCl donates a proton to H₂O, forming hydronium (H₃O⁺) and chloride ions (Cl^-). This illustrates the transformation of reactants into a conjugate acid-base pair: H₂O becomes H₃O⁺ (the conjugate acid) and HCl becomes Cl^- (the conjugate base).

Another example is the reaction between ammonia (NH₃) and water, where NH₃ acts as a base by accepting a proton from H₂O. As NH₃ gains a proton, it becomes ammonium (NH₄⁺), which is the conjugate acid, while H₂O loses a proton, becoming hydroxide (OH^-), the conjugate base. These reactions are not just theoretical—they're the fundamental processes occurring in countless chemical and biological systems all around us.