Amphoterism
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"Amphoteric" redirects here. For other uses, see Amphoteric (disambiguation). Acids and bases | | * Acid dissociation constant * Acid-base extraction * Acid–base reaction * Acid–base titration * Dissociation constant * Acidity function * Buffer solutions * pH * Proton affinity * Amphoterism * Self-ionization of water * Acid strength | Acid types | * Brønsted · * Lewis · * Mineral · * Organic · * Strong · * Superacids · * Weak | Base types | * Brønsted · * Lewis · * Organic · * Strong · * Superbases · * Non-nucleophilic · * Weak | * v · * t · * e |
In chemistry, an amphoteric species is a molecule or ion that can react as an acid as well as a base.[1] The word is derived from the Greek word amphoteroi (ἀμφότεροι) meaning "both". Many metals (such as zinc, tin, lead, aluminium, and beryllium) form amphoteric oxides or hydroxides. Amphoterism depends on the oxidation state of the oxide.
One type of amphoteric species are amphiprotic molecules, which can either donate or accept a proton (H+). Examples include amino acids and proteins, which have amine and carboxylic acid groups, and self-ionizable compounds such as water and ammonia.
Ampholytes are amphoteric molecules that contain both acidic and basic groups and will exist mostly as zwitterions in a certain range of pH. The pH at which the average charge is zero is known as the molecule's isoelectric point. Ampholytes are used to establish a stable pH gradient for use in isoelectric focusing.
Contents
[hide] * 1 Amphoteric oxides and hydroxides[2] * 2 Amphiprotic molecules * 2.1 Examples * 2.2 Not all amphoteric substances are amphiprotic * 3 See also * 4