Question

Identify the Bronsted-Lowry acid and base in each of the following neutralization reactions: (a) \(2 \mathrm{HClO}_{4}(a q)+\mathrm{K}_{2} \mathrm{CO}_{3}(a q) \longrightarrow\) \( 2 \mathrm{KClO}_{4}(a q)+\mathrm{H}_{2} \mathrm{O}(l)+\mathrm{CO}_{2}(g) \) (b) \(\mathrm{NaCN}(a q)+\mathrm{HBr}(a q) \longrightarrow \mathrm{NaBr}(a q)+\mathrm{HCN}(a q)\)

Short answer

(a) \( \text{HClO}_4 \) is the acid, \( \text{K}_2\text{CO}_3 \) is the base. (b) \( \text{HBr} \) is the acid, \( \text{NaCN} \) is the base.

Step-by-step solution

Identify Substances

First, list out the substances involved in each reaction. For reaction (a), we have \( \text{HClO}_4 \), \( \text{K}_2\text{CO}_3 \), \( \text{KClO}_4 \), \( \text{H}_2\text{O} \), and \( \text{CO}_2 \). For reaction (b), we have \( \text{NaCN} \), \( \text{HBr} \), \( \text{NaBr} \), and \( \text{HCN} \).

Determine Acid and Base in Reaction (a)

In reaction (a), \( \text{HClO}_4 \) donates a proton (\( \text{H}^+ \)) to form \( \text{H}_2\text{O} \) and \( \text{CO}_2 \). This makes \( \text{HClO}_4 \) the Bronsted-Lowry acid. \( \text{K}_2\text{CO}_3 \) accepts the protons when forming carbonic acid, which decomposes to \( \text{H}_2\text{O} \) and \( \text{CO}_2 \), making it the base.

Determine Acid and Base in Reaction (b)

In reaction (b), \( \text{HBr} \) donates a proton to \( \text{NaCN} \) to form \( \text{HCN} \). Therefore, \( \text{HBr} \) acts as the Bronsted-Lowry acid because it donates a proton and \( \text{NaCN} \) is the base because it accepts the proton.

Summarize Findings

For reaction (a), \( \text{HClO}_4 \) is the acid and \( \text{K}_2\text{CO}_3 \) is the base. For reaction (b), \( \text{HBr} \) is the acid and \( \text{NaCN} \) is the base.

Key concepts

Neutralization Reactions

In chemistry, a neutralization reaction is when an acid and a base interact to produce water and a salt. It is a fundamental concept in the Bronsted-Lowry acid-base theory. This theory states that acids are proton (H⁺) donors and bases are proton acceptors. When an acid and a base come together in a neutralization reaction, the protons donated by the acid are accepted by the base.

For example, consider reaction (a) from the exercise:
- The components are - the acid: perchloric acid (\( ext{HClO}_4\)) and - the base: potassium carbonate (\( ext{K}_2 ext{CO}_3\)).
- When \( ext{HClO}_4\) donates its protons to the \( ext{K}_2 ext{CO}_3\), water and carbon dioxide are produced. The result is a complete neutralization, resulting in a salt, potassium perchlorate (\( ext{KClO}_4\)).

Neutralization reactions are crucial not only for understanding basic chemistry but also for various applications such as titrations in analytical chemistry to determine concentrations of solutions.

Identifying Acids and Bases

In any chemical reaction, particularly in neutralization reactions, identifying the acid and the base is key. According to the Bronsted-Lowry theory, your focus is on the transfer of protons between the molecules involved. An acid will lose, or donate, a proton, while a base will gain, or accept, the proton.

Let's examine reaction (b) to clarify this process:
- The reactants are hydrobromic acid (\( ext{HBr}\)) and sodium cyanide (\( ext{NaCN}\)).
- \( ext{HBr}\) donates a proton to \( ext{NaCN}\), converting into \( ext{HCN}\). This transfer reveals that \( ext{HBr}\) is the acid because it loses a proton. \( ext{NaCN}\), on the other hand, is the base because it accepts this proton and becomes \( ext{HCN}\).

Recognizing acids and bases requires careful attention to the behavior of each substance during the reaction. An easy tip is to observe the changes in chemical composition: look for ions or molecules that either lose or gain H⁺.

Proton Donation and Acceptance

Understanding proton donation and acceptance is at the heart of Bronsted-Lowry acid-base theory. It revolves around how molecules or ions handle protons.

- **Proton Donation by Acids:**
Acids, as per the Bronsted-Lowry definition, shed one or more protons during a reaction. When an acid ionizes, it releases an H⁺ ion. For instance, in the reaction of \( ext{HClO}_4\) and \( ext{HBr}\), these acids donate their protons to bases that accept them.

- **Proton Acceptance by Bases:**
Bases are molecules or ions that grab protons, often from the surrounding medium or directly from a nearby acid. The base's job is to take in this H⁺ ion, forming a new compound. In our examples, \( ext{K}_2 ext{CO}_3\) and \( ext{NaCN}\) were the bases because they accepted protons from \( ext{HClO}_4\) and \( ext{HBr}\).

Grasping the proton donation and acceptance philosophy imparts a better understanding of why certain substances act as acids and why others behave as bases in chemical reactions. This understanding is instrumental in predicting how substances will react with one another.