Question

Is ${{H}_{2}}S$ a lewis acid or a lewis base?

Answer 1

Lewis base and Lewis acid are more or less equivalent with the words nucleophile and electrophile. However, these words highlight the kinetic component of reactivity, particularly their abstract noun forms nucleophilicity and electrophilicity, whereas Lewis basicity and Lewis acidity emphasise the thermodynamic aspect of Lewis adduct production.

Complete answer:
Lewis acids and bases are electron-pair acceptors and electron-pair donors, respectively, according to the Lewis theory of acid-base reactions. As a result, a Lewis base can transfer two electrons to a Lewis acid, resulting in a product with a coordinate covalent bond. A Lewis adduct is another name for this substance.
${{H}_{2}}S$ is a Lewis acid that may also be used as a Lewis base.
${{H}_{2}}O:+{{H}_{2}}S\rightleftharpoons {{H}_{3}}{{O}^{+}}+S{{H}^{-}}$
The acid ${{H}_{2}}S$ is a weak one. Because it donates a proton to water, ${{H}_{2}}S$ is a Bronsted acid. Because it accepts a pair of electrons to create the $O-H$ bond in the hydronium ion, it is also a Lewis acid. Because the S in ${{H}_{2}}S$ includes two lone pairs, it may also be used as a Lewis base. The ${{H}_{2}}S$ becomes protonated in the presence of a strong acid such as ${{H}_{2}}S{{O}_{4}}$. The${{H}_{2}}S$ is functioning as a Lewis base because it donates an electron pair to establish a bond with the H of ${{H}_{2}}S{{O}_{4}}$.
${{H}_{2}}S:+{{H}_{2}}S{{O}_{4}}\to {{H}_{3}}{{S}^{+}}+HS{{O}_{4}}^{-}$

Note:
Lewis proposed in 1916 that two atoms in a chemical bond are kept together by sharing a pair of electrons. A covalent bond is one in which each atom contributes one electron to the connection. A dative covalent link, also known as a coordinate bond, occurs when both electrons originate from one of the atoms. The ammonia molecule gives a pair of electrons to the proton in the creation of an ammonium ion from ammonia and hydrogen, for example; the identity of the electrons is lost in the ammonium ion that is produced. Nonetheless, Lewis proposed classifying an electron-pair donor as a base and an electron-pair receiver as an acid.