Answer
$H_2S$ is a Lewis acid and a Lewis base.
Work Step by Step
$H_2S$ is a Lewis acid because, it can receive one pair of electrons and make a bond with one of its hydrogen. For example:
$H_2S(aq) + H_2O(l) \lt -- \gt HS^-(aq) + H_3O^+(aq)$
- This only happens because the "S" is more electronegative, making the hydrogens slightly positive, so it can receive electrons from another molecule, and create a bond.
$H_2S$ is a Lewis base because, normally the central atom $(S)$ has 6 electrons in its valence shell, and it is making 2 covalent bonds with the hydrogens, therefore: 6 - 2 = 4, and there are 4 free electrons (2 lone pairs) this molecule can give, making it a Lewis base.
