Amphoteric
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A species that has the potential to act both as an acid and as a base according to Brønsted-Lowry Theory is said to be amphoteric.
eg: Water
The water molecule has hydrogen atoms and, therefore, could act as an acid in a reaction. The oxygen atom in the water molecule has two lone pairs, one of which could be used to form a bond with a \(H^+\(, and, therefore, the water molecule could act as a base in a reaction. Since water has the potential to act both as an acid and as a base, water is amphoteric.
- Gamini Gunawardena from the OChemPal site (Utah Valley University)