Problem 21 - Chemistry An Atoms First Approach

Question

What is an acid and what is a base? An acid-base reaction is sometimes called a proton-transfer reaction. Explain.

Step-by-Step Solution

Answer

Acids are substances that release hydrogen ions (H+) in water, while bases release hydroxide ions (OH-). The Bronsted-Lowry theory defines an acid as a proton (H+) donor and a base as a proton acceptor. In an acid-base reaction, the acid donates a proton to the base, forming a conjugate base and conjugate acid. This proton-transfer process is the basis for the term "proton-transfer reaction." For example, in the reaction HA + B → A- + HB+, HA donates a proton to B, forming A- and HB+.

Step 1: 1. Definition of Acids and Bases

Acids are substances that release hydrogen ions (H+) when they dissolve in water, while bases are substances that release hydroxide ions (OH-) when they dissolve in water. The strength of an acid or base is determined by how completely it releases these ions. Strong acids and bases dissociate completely in water, whereas weak acids and bases do not.

Step 2: 2. Examples of Acids and Bases

Common examples of acids include hydrochloric acid (HCl), sulfuric acid (H2SO4), and acetic acid (CH3COOH). These acids release H+ ions when they dissolve in water, which causes the resulting solution to be acidic. On the other hand, examples of bases include sodium hydroxide (NaOH), potassium hydroxide (KOH), and ammonia (NH3). These bases release OH- ions when they dissolve in water, leading to a basic solution.

Step 3: 3. Bronsted-Lowry Theory of Acids and Bases

The Bronsted-Lowry theory further defines an acid as a proton (Hydrogen ion, H+) donor, and a base as a proton acceptor. In this theory, acids and bases react with each other by transferring a proton from the acid to the base. This proton-transfer process is the basis for the term "proton-transfer reaction."

Step 4: 4. Acid-Base Reactions and Proton-Transfer

In an acid-base reaction, the acid donates a proton (H+) to the base, and the base accepts the proton, resulting in the formation of a new acid and a new base. This process of proton transfer is illustrated in the reaction between a generic acid HA and a generic base B: HA + B → A- + HB+ Here, the acid HA donates a proton to the base B, forming the conjugate base A- and the conjugate acid HB+. Overall, acids and bases are defined by their behavior in terms of proton and hydroxide ion release, and the term "proton-transfer reaction" comes from the Bronsted-Lowry theory, where the basis of acid-base reactions is the transfer of a proton from an acid to a base.