Problem 18 - Chemistry: The Central Science in SI Units, Global Edition

Question

Identify the Brønsted-Lowry acid and the BrønstedLowry base on the left side of each equation, and also identify the conjugate acid and conjugate base of each on the right side. $$ \begin{array}{l} \text { (a) } \mathrm{HBrO}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \rightleftharpoons \mathrm{H}_{3} \mathrm{O}^{+}(a q)+\mathrm{BrO}^{-}(a q) \\\ \text { (b) } \mathrm{HSO}_{4}^{-}(a q)+\mathrm{HCO}_{3}^{-}(a q) \rightleftharpoons \mathrm{SO}_{4}^{2-}(a q)+\mathrm{H}_{2} \mathrm{CO}_{3}(a q) \\ \text { (c) } \mathrm{HSO}_{3}^{-}(a q)+\mathrm{H}_{3} \mathrm{O}^{+}(a q) \rightleftharpoons \mathrm{H}_{2} \mathrm{SO}_{3}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \end{array} $$

Step-by-Step Solution

Answer

(a) Brønsted-Lowry acid: \(HBrO\), base: \(H_2O\), conjugate acid: \(H_3O^{+}\), conjugate base: \(BrO^{-}\) (b) Brønsted-Lowry acid: \(HSO_{4}^{-}\), base: \(HCO_{3}^{-}\), conjugate acid: \(H_2CO_3\), conjugate base: \(SO_{4}^{2-}\) (c) Brønsted-Lowry acid: \(H_{3}O^{+}\), base: \(HSO_{3}^{-}\), conjugate acid: \(H_2SO_3\), conjugate base: \(H_2O\)

Step 1: Identify the Brønsted-Lowry acid and base

Compare the species on the left side. Look for species that are donating or accepting a proton. Here, \(HBrO\) donates a proton to \(H_2O\). So, \(HBrO\) is the acid and \(H_2O\) is the base.

Step 2: Identify the conjugate acid and base

On the right side, after the reaction has taken place, the species formed after accepting the proton is the conjugate acid and the species formed after donating the proton is the conjugate base. In this case, \(H_3O^{+}\) is the conjugate acid and \(BrO^-\) is the conjugate base. (b) \(HSO_{4}^{-}(aq) + HCO_{3}^{-}(aq) \rightleftharpoons SO_{4}^{2-}(aq) + H_{2}CO_{3}(aq) \)

Step 1: Identify the Brønsted-Lowry acid and base

Let's compare the species on the left side. Here, \(HSO_{4}^-\) donates a proton to \(HCO_3^-\). So, \(HSO_{4}^-\) is the acid and \(HCO_3^-\) is the base.

Step 2: Identify the conjugate acid and base

On the right side, after the reaction, the species formed after accepting the proton is the conjugate acid and the species formed after donating the proton is the conjugate base. In this case, \(H_2CO_{3}\) is the conjugate acid and \(SO_{4}^{2-}\) is the conjugate base. (c) \(HSO_{3}^{-}(aq) + H_{3}O^{+}(aq) \rightleftharpoons H_{2}SO_{3}(aq) + H_{2}O(l) \)

Step 1: Identify the Brønsted-Lowry acid and base

Lets compare the species on the left side. In this reaction, \(H_{3}O^{+}\) donates a proton to \(HSO_3^{-}\). So, \(H_{3}O^{+}\) is the acid and \(HSO_3^{-}\) is the base.

Step 2: Identify the conjugate acid and base

On the right side, after the reaction, the species formed after accepting the proton is the conjugate acid and the species formed after donating the proton is the conjugate base. In this case, \(H_2SO_3\) is the conjugate acid and \(H_2O\) is the conjugate base.

Key Concepts

Acid-Base Reactions

In the fascinating world of chemistry, acid-base reactions are fundamental processes where acids and bases interact with each other. These reactions involve the transfer of protons (hydrogen ions, \( H^+ \)) from one species to another. According to the Brønsted-Lowry theory, an acid is a substance that can donate a proton, while a base is one that can accept a proton. This definition broadens the traditional concept of acids and bases, allowing us to explore a wider array of chemical reactions.
These reactions can be represented in equations, where the reactants on the left undergo a transformation to produce products on the right. For example, in the reaction:
\[\text{HBrO} + \text{H}_2\text{O} \rightleftharpoons \text{H}_3\text{O}^+ + \text{BrO}^-\]The molecule \( \text{HBrO} \), acting as an acid, donates a proton to \( \text{H}_2\text{O} \), which acts as a base and accepts the proton. The products, \( \text{H}_3\text{O}^+ \) and \( \text{BrO}^- \), illustrate how substances can change from acids to bases and vice versa, leading us to the concept of conjugate acid-base pairs.

Conjugate Acid-Base Pairs

Conjugate acid-base pairs are a unique feature of the Brønsted-Lowry acid-base theory. When a proton is transferred from an acid to a base, the acid turns into what is called its conjugate base, and the base turns into its conjugate acid. This pairing helps in maintaining the balance and continuity of acid-base systems.
In any given reaction, such as:
\[\text{HSO}_4^- + \text{HCO}_3^- \rightleftharpoons \text{SO}_4^{2-} + \text{H}_2\text{CO}_3\]Here, \( \text{HSO}_4^- \) loses a proton to become \( \text{SO}_4^{2-} \), its conjugate base. Meanwhile, \( \text{HCO}_3^- \) gains a proton, forming \( \text{H}_2\text{CO}_3 \), its conjugate acid. This pairing is crucial for understanding how substances can buffer changes in pH and resist drastic alterations in acidity or basicity. Recognizing these pairs is key to predicting the outcome and behavior of acid-base reactions.

Proton Transfer

Proton transfer is the heart of the Brønsted-Lowry acid-base theory. It describes the movement of protons from acids to bases, driving the transformation of chemical species during a reaction. This transfer significantly influences the chemical properties of the substances involved.
Take, for instance, the reaction:
\[\text{HSO}_3^- + \text{H}_3\text{O}^+ \rightleftharpoons \text{H}_2\text{SO}_3 + \text{H}_2\text{O}\]Here, \( \text{H}_3\text{O}^+ \) transfers a proton to \( \text{HSO}_3^- \), resulting in the formation of \( \text{H}_2\text{SO}_3 \) and \( \text{H}_2\text{O} \). The proton transfer is responsible for altering the physical and chemical characteristics of the original molecules, leading to the formation of new conjugate pairs.
Understanding proton transfer is not only vital for grasping acid-base chemistry but also for wider applications, including biological processes and industrial applications where acid and base interactions are fundamental.