Problem 96 - Chemistry The Central Science In Si Units

Question

Identify the Lewis acid and Lewis base in each of the following reactions: (a) \(\mathrm{HNO}_{2}(a q)+\mathrm{OH}^{-}(a q) \rightleftharpoons \mathrm{NO}_{2}^{-}(a q)+\mathrm{H}_{2} \mathrm{O}(l)\) (b) \(\mathrm{FeBr}_{3}(s)+\mathrm{Br}^{-}(a q) \rightleftharpoons \mathrm{FeBr}_{4}^{-}(a q)\) (c) \(\mathrm{Zn}^{2+}(a q)+4 \mathrm{NH}_{3}(a q) \rightleftharpoons \mathrm{Zn}\left(\mathrm{NH}_{3}\right)_{4}{\underline{\phantom{xx}}}^{2+}(a q)\) (d) \(\mathrm{SO}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(l) \rightleftharpoons \mathrm{H}_{2} \mathrm{SO}_{3}(a q)\)

Step-by-Step Solution

Answer

(a) \(\mathrm{Lewis \ Acid: \ OH^-}\), \(\mathrm{Lewis \ Base: \ HNO_2}\); (b) \(\mathrm{Lewis \ Acid: \ FeBr_3}\), \(\mathrm{Lewis \ Base: \ Br^-}\); (c) \(\mathrm{Lewis \ Acid: \ Zn^{2+}}\), \(\mathrm{Lewis \ Base: \ NH_3}\); (d) \(\mathrm{Lewis \ Acid: \ SO_2}\), \(\mathrm{Lewis \ Base: \ H_2O}\).

Step 1: Understand Lewis Acid and Base

A Lewis acid is a species that accepts an electron pair, while a Lewis base is a species that donates an electron pair.

Step 2: Analyze Reaction (a)

In the reaction \(\mathrm{HNO}_{2}(a q)+\mathrm{OH}^{-}(a q) \rightleftharpoons \mathrm{NO}_{2}^{-}(a q)+\mathrm{H}_{2} \mathrm{O}(l)\), \(\mathrm{HNO}_2\) donates a proton (\(\mathrm{H}^+\)) to \(\mathrm{OH}^-\), which accepts it. Therefore, \(\mathrm{HNO}_2\) is the Lewis base and \(\mathrm{OH}^-\) is the Lewis acid.

Step 3: Analyze Reaction (b)

In the reaction \(\mathrm{FeBr}_{3}(s)+\mathrm{Br}^{-}(a q) \rightleftharpoons \mathrm{FeBr}_{4}^{-}(a q)\), the \(\mathrm{FeBr}_3\) accepts an electron pair from \(\mathrm{Br}^-\) to form \(\mathrm{FeBr}_4^-\). Therefore, \(\mathrm{FeBr}_3\) is the Lewis acid and \(\mathrm{Br}^-\) is the Lewis base.

Step 4: Analyze Reaction (c)

In the reaction \(\mathrm{Zn}^{2+}(a q)+4 \mathrm{NH}_{3}(a q) \rightleftharpoons \mathrm{Zn}\left(\mathrm{NH}_{3}\right)_{4}{\underline{\phantom{xx}}}^{2+}(a q)\), \(\mathrm{Zn}^{2+}\) accepts electron pairs from the \(\mathrm{NH}_3\) molecules. Thus, \(\mathrm{Zn}^{2+}\) is the Lewis acid and \(\mathrm{NH}_3\) is the Lewis base.

Step 5: Analyze Reaction (d)

In the reaction \(\mathrm{SO}_{2}( ext{g})+\mathrm{H}_{2} \mathrm{O}(l) \rightleftharpoons \mathrm{H}_{2} \mathrm{SO}_{3}(aq)\), \(\mathrm{SO}_2\) accepts an electron pair from water as new bonds are formed to create \(\mathrm{H}_2\mathrm{SO}_3\). Therefore, \(\mathrm{SO}_2\) is the Lewis acid, and \(\mathrm{H_2O}\) is the Lewis base.

Key Concepts

Lewis Acid

In chemistry, a Lewis acid is a molecule or ion that accepts an electron pair from another molecule or ion during a chemical reaction. This concept is based on the Lewis theory of acids and bases, named after Gilbert N. Lewis. It focuses on the transfer and sharing of electron pairs.A Lewis acid can be any of the following:

• A positively charged ion, such as metal cations like \(\mathrm{Zn}^{2+} \)
• A molecule with an electron-deficient atom, such as \(\mathrm{SO}_2 \)

Lewis acids are crucial in many reactions, such as the formation of complex ions and in various catalysis processes. The role these acids play involves accepting electrons to form new bonds, ultimately leading to new chemical substances.

Lewis Base

A Lewis base is defined as an electron pair donor. In the context of Lewis acid-base reactions, a base donates an electron pair to form a coordinate bond with a Lewis acid. Think of it as a partner in a dance, where one molecule gives and the other takes.Common characteristics include:

• Presence of a lone pair of electrons ready to be donated, for example, ammonia \(\mathrm{(NH}_3 )\).
• Negatively charged ions, like \(\mathrm{Br}^{-} \), which have extra electrons to share.

When participating in reactions, Lewis bases often result in new structures, such as the formation of \(\mathrm{FeBr}_4^{-} \) from \(\mathrm{Br}^{-} \) and \(\mathrm{FeBr}_3\). Recognizing Lewis bases helps in predicting product compositions in chemical reactions.

Electronic Structure

Understanding the electronic structure of molecules and ions is fundamental in chemistry. Electronic structure determines how atoms and molecules interact in a reaction. Key aspects include:

• The arrangement of electrons around an atom, which influences its reactivity. For example, electron-rich species like \(\mathrm{NH}_3 \) tend to donate electrons.
• Orbitals and electron configurations, which dictate how atoms bond and form size and angles in molecular structures.

Recognizing electron pairs and their distribution helps in identifying potential Lewis acids and bases in a chemical reaction. This clarity on electron configurations aids in comprehending how molecules will interact.

Chemistry Education

Chemistry education is pivotal in nurturing scientific understanding. It involves teaching fundamental concepts and principles that explain the behavior of matter. By integrating different theories like Lewis acid-base theory, students gain a comprehensive view of how substances interact. Effective chemistry education includes:

• Hands-on experiments to demonstrate concepts like electron transfer in Lewis acid-base reactions.
• Discussion of real-world applications and how Lewis concepts apply to industry and environment.
• Encouraging problem-solving skills by working through reactions step-by-step.

Such educational approaches ensure students not only memorize facts but also understand how and why reactions occur.