Problem 30 - General Chemistry: Principles and Modern Applications

Question

A neutralization reaction between an acid and a base is a common method of preparing useful salts. Give net ionic equations showing how the following salts could be prepared in this way: (a) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{HPO}_{4};\) (b) \(\mathrm{NH}_{4} \mathrm{NO}_{3} ;\) and \((\mathrm{c})\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\).

Step-by-Step Solution

Answer

The equations are: 1. \(\mathrm{NH}_{3}\) + \(\mathrm{H}_{2}\mathrm{HPO}_{4}\) -> \((\mathrm{NH}_{4})_{2} \mathrm{HPO}_{4}\) 2. \(\mathrm{NH}_{3}\) + \(\mathrm{HNO}_{3}\) -> \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) 3. 2\(\mathrm{NH}_{3}\) + \(\mathrm{H}_{2}\mathrm{SO}_{4}\) -> \((\mathrm{NH}_{4})_{2} \mathrm{SO}_{4}\)

Step 1: Equation for \((\mathrm{NH}_{4})_{2} \mathrm{HPO}_{4}\)

First, let's find the acids and bases for this salt. We see the salt is formed of \(\mathrm{NH}_{4}^{+}\) and \(\mathrm{HPO}_{4}^{2-}\). Recognizing these ions, you might have used \(\mathrm{NH}_{3}\), ammonia, as the base and \(\mathrm{H}_{2}\mathrm{HPO}_{4}\), dihydrogen phosphate, as the acid. The equation would go as: \(\mathrm{NH}_{3}\) + \(\mathrm{H}_{2}\mathrm{HPO}_{4}\) -> \((\mathrm{NH}_{4})_{2} \mathrm{HPO}_{4}\)

Step 2: Equation for \(\mathrm{NH}_{4} \mathrm{NO}_{3}\)

For this salt, we can recognize the ions as \(\mathrm{NH}_{4}^{+}\) and \(\mathrm{NO}_{3}^{-}\). In this case, we could have chosen \(\mathrm{NH}_{3}\), as the base and \(\mathrm{HNO}_{3}\), nitric acid, as the acid. The equation would then go: \(\mathrm{NH}_{3}\) + \(\mathrm{HNO}_{3}\) -> \(\mathrm{NH}_{4} \mathrm{NO}_{3}\)

Step 3: Equation for \((\mathrm{NH}_{4})_{2} \mathrm{SO}_{4}\)

With this salt, the ions are \(\mathrm{NH}_{4}^{+}\) and \(\mathrm{SO}_{4}^{2-}\). For this reaction, \(\mathrm{NH}_{3}\) would be the base and \(\mathrm{H}_{2}\mathrm{SO}_{4}\), sulfuric acid, would be the acide. Therefore, the equation is: 2\(\mathrm{NH}_{3}\) + \(\mathrm{H}_{2}\mathrm{SO}_{4}\) -> \((\mathrm{NH}_{4})_{2} \mathrm{SO}_{4}\)

Key Concepts

Ionic Equations

In a neutralization reaction, an ionic equation is a simplified representation showing only the species that actually change during the reaction. This makes them very useful for visualizing the underlying chemistry, especially during acid-base reactions. For example, when preparing the salt \((\mathrm{NH}_{4})_{2}\mathrm{HPO}_{4}\), write the equation as: \[ \mathrm{NH_{3}} (aq) + \mathrm{H_{2}PO_{4}}^{-} (aq) \rightarrow \mathrm{NH_{4}}^{+} (aq) + \mathrm{HPO_{4}}^{2-} (aq) \]. Here, \(\mathrm{NH_{4}}^{+}\) and \(\mathrm{HPO_{4}}^{2-}\) are the components that actually change, leading straight to the net ionic equation. This guide helps clarify which species to focus on. Never include unchanged ions in the final formula. Completely understanding ionic equations enhances comprehension of complex reactions.

Acid-Base Reactions

These reactions play a critical role in the formation of salts such as ammonium nitrate\(\mathrm{NH}_{4}\mathrm{NO}_{3}\). When considered through the lens of acid-base interactions, acids are chemicals that donate protons \((\mathrm{H}^{+})\) while bases accept them. For example, the reaction with nitric acid \((\mathrm{HNO}_{3})\) acting as the acid and ammonia \((\mathrm{NH}_{3})\) as the base can be written as follows: \[ \mathrm{NH_{3}} + \mathrm{HNO_{3}} \rightarrow \mathrm{NH_{4}^{+}} + \mathrm{NO_{3}^{-}} \]. Understanding the flow of protons from acids to bases reveals why these reactions result in salt formation. With such reactions, not only do you see salt creation, but water is often released as a byproduct.

Salt Preparation

In chemistry, preparing salts through neutralization reactions is essential for obtaining a broad range of compounds. Salts like ammonium sulfate \((\mathrm{NH}_{4})_{2}\mathrm{SO}_{4}\) are created when a specific acid and base pair off in a reaction. - Use the base \(\mathrm{NH}_{3}\) and acid \(\mathrm{H}_{2}\mathrm{SO}_{4}\).- Combine them in a reaction \[ 2\mathrm{NH_{3}} + \mathrm{H}_{2}\mathrm{SO}_{4} \rightarrow (\mathrm{NH}_{4})_{2}\mathrm{SO}_{4} \].This method helps students learn about different salts and how they are produced from corresponding acids and bases. The ability to predict the products of such reactions is critical for solving more complicated chemical problems. Being familiar with the process of salt preparation aids in both academic challenges and practical laboratory situations.