Question

Classify each of the following as a Lewis acid or a Lewis base. Drag the appropriate items to their respective bins. H-, I-, Fe3+, NO2, SnCl4, CH3OH, (CH3)3N

Answer 1

Concepts and reason

The concept used to solve this problem is based on Lewis acid and Lewis base. Cations and species with an incomplete octet of electrons come under the category of Lewis acids. Anions, lone-pair containing species, and electron-rich \(\pi-\) system, all come under the category of Lewis bases.

Fundamentals

According to Lewis's theory of acid-base reactions, a Lewis acid is a chemical species (ion or molecule) having the capacity of accepting a pair of nonbonding electrons. A Lewis acid must have vacant orbitals to be able to accept electrons. A Lewis base is a chemical species (ion or molecule) having the capacity of donating a pair of nonbonding electrons.

 

\(\mathrm{H}^{-}\) (hydride ion) has non-bonding electrons and can donate these electrons to other compounds. The \(\mathrm{H}^{-}\) is a Lewis base.

\(\mathrm{H}^{-}\) has lone pair of electrons and can donate it. The lone pair containing species come under the category of Lewis bases.

 

\(\mathrm{I}^{-}\) (iodide ion) has non-bonding electrons and can donate these electrons to other compounds. The \(\mathrm{I}^{-}\) is a Lewis base.

\(\mathrm{I}^{-}\) has lone pair of electrons and can donate it. The lone pair containing species come under the category of Lewis bases.

 

\(\mathrm{Fe}^{3+}\) is a cation. It can easily accept lone pair of electrons and can also expand its octet. The \(\mathrm{Fe}^{3+}\) is a Lewis acid.

Cations come under the category of Lewis acid. Thus, \(\mathrm{Fe}^{3+}\) is a Lewis acid.

 

\(\mathrm{NO}_{2}\) is an electron-deficient species thus, it can accept an electron. The \(\mathrm{NO}_{2}\) is a Lewis acid.

\(\mathrm{NO}_{2}\) exists as a free radical in the atmosphere. It is often written as \(^{\bullet} \mathrm{NO}_{2}\). since free radicals are electron-deficient species, therefore \(\mathrm{NO}_{2}\) comes under the category of Lewis acid.

 

\(\mathrm{SnCl}_{4}\) has empty d-orbitals in its central atom, \(\mathrm{Sn}\) The \(\operatorname{Sn} \mathrm{Cl}_{4}\) is a Lewis acid.

The metal ion in \(\mathrm{SnCl}_{4}\) can expand its octet by accepting electrons. Thus, \(\mathrm{SnCl}_{4}\) is a Lewis acid.

 

\(\mathrm{CH}_{3} \mathrm{OH}\) (methanol) has non-bonding electrons and can donate these electrons to other compounds. The \(\mathrm{CH}_{3} \mathrm{OH}\) is a Lewis base.

\(\mathrm{CH}_{3} \mathrm{OH}\) has lone pair of electrons and can donate it. The lone pair containing species come under the category of Lewis bases.

 

\(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}\) or trimethylamine has non-bonding electrons and can donate these electrons to other compounds. The \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}\) is a Lewis base.

The chemical species in their respective bins are:

$$ \begin{array}{|l|l|} \hline \text { Lewis acid } & \text { Lewis base } \\ \hline \mathrm{Fe}^{3+} & \mathrm{H}^{-} \\ \mathrm{NO}_{2} & \mathrm{I}^{-} \\ \mathrm{SnCl}_{4} & \mathrm{CH}_{3} \mathrm{OH} \\ & \left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N} \\ \hline \end{array} $$

\(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}\) has lone pair of electrons and can donate it. The lone pair containing species come under the category of Lewis bases.