Problem 101 - Chemistry Matter and Change

Question

Identify whether each of the reactants in these reactions is acting as an acid or a base. (Chapter 18\()\) a. \(\mathrm{HBr}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{H}_{3} \mathrm{O}^{+}+\mathrm{Br}^{-}\) b. \(\mathrm{NH}_{3}+\mathrm{HCOOH} \rightarrow \mathrm{NH}_{4}^{+}+\mathrm{HCOO}^{-}\) c. \(\mathrm{HCO}_{3}^{-}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{CO}_{3}^{-}+\mathrm{H}_{3} \mathrm{O}^{+}\)

Step-by-Step Solution

Answer

a. \( \mathrm{HBr} \) is an acid, \( \mathrm{H}_{2} \mathrm{O} \) is a base. b. \( \mathrm{HCOOH} \) is an acid, \( \mathrm{NH}_{3} \) is a base. c. \( \mathrm{HCO}_{3}^{-} \) is an acid, \( \mathrm{H}_{2} \mathrm{O} \) is a base.

Step 1: Analyze Reaction a

In reaction \( \mathrm{HBr} + \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{H}_{3} \mathrm{O}^{+} + \mathrm{Br}^{-} \), \( \mathrm{HBr} \) donates a proton to \( \mathrm{H}_{2} \mathrm{O} \), producing \( \mathrm{Br}^{-} \) and \( \mathrm{H}_{3} \mathrm{O}^{+} \). Thus, \( \mathrm{HBr} \) acts as the acid, and \( \mathrm{H}_{2} \mathrm{O} \) acts as the base.

Step 2: Analyze Reaction b

In reaction \( \mathrm{NH}_{3} + \mathrm{HCOOH} \rightarrow \mathrm{NH}_{4}^{+} + \mathrm{HCOO}^{-} \), \( \mathrm{HCOOH} \) donates a proton to \( \mathrm{NH}_{3} \), becoming \( \mathrm{HCOO}^{-} \). Hence, \( \mathrm{HCOOH} \) is the acid, and \( \mathrm{NH}_{3} \) is the base.

Step 3: Analyze Reaction c

In reaction \( \mathrm{HCO}_{3}^{-} + \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{CO}_{3}^{-} + \mathrm{H}_{3} \mathrm{O}^{+} \), \( \mathrm{HCO}_{3}^{-} \) donates a proton to \( \mathrm{H}_{2} \mathrm{O} \), forming \( \mathrm{CO}_{3}^{-} \). Thus, \( \mathrm{HCO}_{3}^{-} \) acts as the acid, and \( \mathrm{H}_{2} \mathrm{O} \) acts as the base.

Key Concepts

Proton Donor

In the realm of chemistry, particularly in acid-base reactions, a proton donor is crucial. Simply put, a proton donor is a substance that relinquishes a hydrogen ion (H\(^+\)) during a chemical reaction.
This ion is essentially a proton without electrons. Substances that donate protons play a pivotal role in chemical reactions as they form new compounds.During an acid-base reaction, such as the one involving \(\mathrm{HBr}\) and \(\mathrm{H}_2 \mathrm{O}\), the \(\mathrm{HBr}\) acts as a proton donor. It provides a hydrogen ion to water, transforming the water molecule into \(\mathrm{H}_3\mathrm{O}^+\). Similarly, in reactions with \(\mathrm{HCOOH}\), the compound donates its proton to ammonia, \(\mathrm{NH}_3\), illustrating its role as a proton donor. Understanding these interactions is a key step in grasping larger concepts of acid-base chemistry.

Proton Acceptor

In contrast to a proton donor, a proton acceptor is a substance that gains or receives a hydrogen ion, denoted as H\(^+\). This acceptance is fundamental to several chemical reactions as it alters the acceptor's structure and properties.
Proton acceptors are essential for the balance and completion of acid-base reactions.Taking a closer look at reaction scenarios, water (\(\mathrm{H}_2 \mathrm{O}\)) often plays the role of a proton acceptor. For example, during the interaction with \(\mathrm{HBr}\), \(\mathrm{H}_2 \mathrm{O}\) accepts a proton to form hydronium \(\mathrm{H}_3\mathrm{O}^+\). Similarly, in a setup where \(\mathrm{NH}_3\) interacts with \(\mathrm{HCOOH}\), \(\mathrm{NH}_3\) acts as the proton acceptor, forming ammonium ions (\(\mathrm{NH}_4^+\)). These acceptance processes are crucial in understanding how compounds function within different reactions.

Bronsted-Lowry Acid

The Bronsted-Lowry theory provides a broader perspective on acids and bases by defining them according to their ability to donate or accept protons. A Bronsted-Lowry acid is any substance that can donate a proton (H\(^+\)) during a reaction.
This theory moves beyond traditional definitions by focusing on proton transfer.Examples of Bronsted-Lowry acids can be observed in the reactions provided. \(\mathrm{HBr}\), which donates a proton in the reaction with water, is an example of a Bronsted-Lowry acid. Additionally, \(\mathrm{HCOOH}\) donates a proton to formate ions when reacting with ammonia. The versatility of the Bronsted-Lowry theory lies in its ability to categorize acids by their immediate impact on their environment through proton donation.

Bronsted-Lowry Base

Complementing the concept of Bronsted-Lowry acids, a Bronsted-Lowry base is recognized as any substance capable of accepting a proton. This definition widens the understanding of basicity, as it involves the interaction with protons rather than limiting it to hydroxide ions.
Looking closer at the reactions highlighted, when \(\mathrm{H}_2 \mathrm{O}\) accepts a proton from \(\mathrm{HBr}\), it becomes \(\mathrm{H}_3\mathrm{O}^+\), demonstrating its role as a Bronsted-Lowry base. Another instance can be seen with ammonia (\(\mathrm{NH}_3\)); as it absorbs a proton from formic acid, transforming into ammonium (\(\mathrm{NH}_4^+\)), it acts as a Bronsted-Lowry base here. Understanding this concept is pivotal for conceptualizing how bases can interact within various chemical contexts beyond just forming salts or neutralizing acids.