Amphoteric Nature of Water - QS Study
QS Study

Water is amphoteric meaning that it can act as both an acid and a base. The amphoteric characteristic of water is important in the acid-base properties of aqueous solutions.

HNO3 (aq) + H2 O (I) ↔ NO3 (aq) + H3O+ (aq)

In the forward reaction, HNO3 donates a proton to H2O. Thus, HNO3 is an acid and H2O is here a base.

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In the backward reaction, NO3 accepts a proton from H3O+. Thus, NO3 is an acid and H2O is a base.

NH3 (aq) + H2O (I) → NH4+ (aq) + OH (aq)

In this forward reaction, NH3 accepts a proton from H2O. Thus, NH3 is a base and H2O is an acid. In the backward reaction, NH4+ donates a proton to the OH. Here, the OH is a base and NH4+ is an acid.