Final answer:
Water (H₂O) is amphoteric and can act as both a Lewis acid and a Lewis base, acting as a base by donating an electron pair to form H₃O+ and as an acid by accepting an electron pair in a reaction with NH₃ to form NH4+.
Step-by-step explanation:
The question asks which of the following species can act as both a Lewis acid and a Lewis base among H₂O, NH₃, CO₂, and HCl. A species that can act as both a Lewis acid and a Lewis base is referred to as amphoteric. In the context of Lewis theory, a Lewis acid is an electron pair acceptor, whereas a Lewis base is an electron pair donor. Among the choices, water (H₂O) is known to be amphoteric.
- H₂O acts as a Lewis base when it donates a pair of electrons to a proton, forming hydronium ion (H₃O+), as seen in this equation: H₂O(l) + H+ → H₃O+ (aq).
- H₂O acts as a Lewis acid when it accepts a pair of electrons from a base such as ammonia (NH₃), as shown in this reaction: NH₃ + H₂O → NH₄+ + OH−.
In conclusion, H₂O (water) can act as both a Lewis acid and a Lewis base, fulfilling the requirements of the question.