Problem 38 - Chemistry A Molecular Approach

Question

Write the formula for the conjugate acid of each base. a. \(\mathrm{NH}_{3}\) b. \(\mathrm{ClO}_{4}^{-}\) c. \(\mathrm{HSO}_{4}^{-}\) d. \(\mathrm{CO}_{3}^{2-}\)

Step-by-Step Solution

Answer

The conjugate acids are: a. \(\mathrm{NH}_{4}^{+}\), b. \(\mathrm{HClO}_{4}\), c. \(\mathrm{H}_{2}\mathrm{SO}_{4}\), d. \(\mathrm{HCO}_{3}^{-}\).

Step 1: Understanding Conjugate Acids

The conjugate acid of a base is formed when the base accepts a proton (H+). Using the formula of the base, the conjugate acid can be written by adding an H+ to the base and increasing the charge by +1.

Step 2: Conjugate Acid of \(\mathrm{NH}_{3}\)

Starting with the base \(\mathrm{NH}_{3}\), accept a proton (H+) to form \(\mathrm{NH}_{4}^{+}\), which is the conjugate acid.

Step 3: Conjugate Acid of \(\mathrm{ClO}_{4}^{-}\)

Starting with the base \(\mathrm{ClO}_{4}^{-}\), accept a proton (H+) to form \(\mathrm{HClO}_{4}\), which is the conjugate acid with no charge.

Step 4: Conjugate Acid of \(\mathrm{HSO}_{4}^{-}\)

Starting with the base \(\mathrm{HSO}_{4}^{-}\), accept a proton (H+) to form \(\mathrm{H}_{2}\mathrm{SO}_{4}\), which is the conjugate acid with no charge.

Step 5: Conjugate Acid of \(\mathrm{CO}_{3}^{2-}\)

Starting with the base \(\mathrm{CO}_{3}^{2-}\), accept a proton (H+) to form \(\mathrm{HCO}_{3}^{-}\), which is the conjugate acid with a charge of -1.

Key Concepts

Acid-Base Chemistry

Acid-base chemistry is a fundamental concept that deals with the transfer of protons (H+) between substances. In this branch of chemistry, an acid is defined as a substance that can donate a proton, while a base is a substance that can accept a proton. An important concept in acid-base chemistry is the conjugate acid-base pair. When a base gains a proton, it becomes its conjugate acid, just as when an acid loses a proton, it forms its conjugate base. This relationship is an essential part of the Brønsted-Lowry acid-base theory.

The strength of an acid or base is indicated by its dissociation in water. Strong acids and bases dissociate completely, while weak ones only partially dissociate. This difference not only influences the pH of a solution but also the acid's or base's ability to participate in reactions. The conjugate acid of a weak base tends to be a weak acid, and similarly, the conjugate base of a weak acid is usually a weak base.

Proton Acceptance

Proton acceptance is a key part of understanding how bases operate within acid-base reactions. A base's ability to accept a proton is what converts it into its conjugate acid. In chemical reactions, especially those in aqueous solutions, bases typically accept protons from water or from other acid species available, forming their corresponding conjugate acids.

For example, ammonia (H_3) is a common weak base; when it encounters a proton donor, it readily accepts a proton to form ammonium (H_4^+), demonstrating proton acceptance. This interaction is reversible, which is why we often talk about equilibrium in these systems. The tendency of a base to accept a proton and the stability of the resulting conjugate acid can vastly affect reaction mechanisms and the direction of chemical equilibria.

Chemical Formulas

Chemical formulas are vital tools that represent the composition of a chemical compound. They indicate the types of atoms present and the exact number of each atom in a molecule. Understanding chemical formulas is crucial when discussing acid-base chemistry, as they allow us to visualize the changes that occur during the reaction, such as the acceptance of a proton by a base to form its conjugate acid.

When a base accepts a proton, this not only changes the chemical structure but also the formula. For instance, carbonate ion (CO_3^{2-}) accepts a proton to become bicarbonate (HCO_3^{-}). This demonstrates both the formula change and the chemical process of proton acceptance. Students should be comfortable with writing and interpreting chemical formulas to fully grasp these changes and to understand the properties of the substances before and after a reaction.