Amphiprotic
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In chemistry, a substance is described as amphiprotic if it can both donate or accept a proton, thus acting either like an acid or a base (acording to Brønsted-Lowry theory of acids and bases: acids are proton donors and bases are proton acceptors. In Lewis theory of acids and bases; acids are electron acceptors and bases are electron donors). Water, amino acids, hydrogen carbonate ions and hydrogen sulfate ions are common examples of amphiprotic species. Since they can donate a proton, all amphiprotic substances contain a hydrogen atom. Also, since they can act like an acid or a base, they are amphoteric. Amphoteric substances, however, are not necessarily amphiprotic.
Example
A common example is the hydrogen carbonate ion, which can act as a base:
HCO3- + H3O+ → H2CO3 + H2O
Or as an acid:
HCO3- + H2O → CO32- + H3O+
Thus, it can effectively accept or donate a proton. Water is the most common example of an amphiprotic substance.