Water as an Acid or Base

[DanielleNario1A]

When do you know if H2O acts as an acid or base?

[Ashley Zhu 1A]

Whether H2O will act as an acid or base depends on the nature of the compound it is reacting with. For example, if water were to react with ammonia (a weak base), then it would be an acid: NH3 + H2O --> NH4+ + OH- (water is donating its proton and ammonia is accepting it). If water were to react with hydrochloric acid, then it would be a base: HCl + H2O --> Cl- + H3O+ (water is accepting the proton and hydrochloric acid is donating it).

[George Ghaly 2L]

Due to it's neutral pH, water can be considered as either a base or an acid. It could gain a proton and become hydronium or lose a proton and become hydroxide.

[Ian Marquez 2K]

When looking at an equilibrium, it is helpful to note whether the reaction other than water is a base or acid. This tells you that water has to act the opposite in this equilibrium reaction because the water either loses a proton to donate to the base (acid) or gains a proton from the acidic donor (base).

[Sarah Fatkin 4I]

Water is amphoteric, meaning that it can act as both an acid and a base. It's useful to look at the other reactant in order to determine whether water is acting as an acid or as a base. For example combining water and hydrochloric acid (HCl), water acts as a base by accepting protons. Hope this helps!