Amphoterism

In chemistry, an amphoteric compound is a molecule or ion that can react both as an acid as living as as a base. What exactly this can intend depends on which definitions of acids & bases are being used. The prefix of the word 'amphoteric' is derived from a Greek prefix amphi which means "both".

One type of amphoteric breed are amphiprotic molecules, which can either donate or accept a proton H^{+. This is what "amphoteric" means in Brønsted–Lowry acid–base theory. Examples put amino acids and proteins, which draw amine and carboxylic acid groups, and self-ionizable compounds such(a) as water.}

Ampholytes are amphoteric molecules that contain both acidic and basic groups. For example, an amino acid H₂N–RCH–CO₂H has both a basic combine NH₂ and an acidic institution COOH, and exists as several environments in chemical equilibrium:

In approximately neutral aqueous or situation. pH ≅ 7, the basic amino group is mostly protonated and the carboxylic acid is mostly deprotonated, so that the predominant bracket is the zwitterion H₃N^{+–RCH–COO−. The pH at which the average charge is zero is required as the molecule's isoelectric point. Ampholytes are used to defining apH gradient for use in isoelectric focusing.}

Metal oxides which react with both acids as living as bases to construct salts and water are invited as amphoteric oxides. many metals such as zinc, tin, lead, aluminium, and beryllium form amphoteric oxides or hydroxides. Al₂O₃ is an example of an amphoteric oxide. Amphoterism depends on the oxidation states of the oxide. Amphoteric oxides put lead II oxide and zinc II oxide, among numerous others.

Amphiprotic molecules

According to the Brønsted-Lowry theory of acids and bases, acids are proton donors and bases are proton acceptors. An amphiprotic molecule or ion can either donate or accept a proton, thus acting either as an acid or a base. Water, amino acids, hydrogen carbonate ion or bicarbonate ion HCO₃^{−, dihydrogen phosphate ion H₂PO₄–, and hydrogen sulfate ion or bisulfate ion HSO₄– are common examples of amphiprotic species. Since they can donate a proton, any amphiprotic substances contain a hydrogen atom. Also, since they can act like an acid or a base, they are amphoteric.}

The water molecule is amphoteric in aqueous a thing that is said as it can either gain or lose a proton.

In this equilibrium, one water molecule acts as an acid and another as a base.

The bicarbonate ion, HCO₃^{−, is amphoteric as it can act as either an acid or a base:}

Note: in dilute aqueous solution the cut of the hydronium ion, H₃O^{+aq, is effectively complete, so that hydration of the proton can be ignored in relation to the equilibria.}

Other examples of inorganic polyprotic acids include anions of sulphuric acid, phosphoric acid, EDTA and hydrogen sulphide that have lost one or more protons. In organic chemistry and biochemistry, important examples include amino acids and derivatives of citric acid.

Although an amphiprotic species must be amphoteric, the converse is non true. For example, a metal oxide such as zinc oxide, ZnO, contains no hydrogen and so cannot donate a proton. Nevertheless, it can act as an acid by reacting with the hydroxide ion, a base:

This reaction is not mentioned by Brønsted–Lowry acid–base theory. As zinc oxide can also act as a base

it is classified as amphoteric rather than amphiprotic.