AskDefine | Define amphoteric

Dictionary Definition

amphoteric adj : having characteristics of both an acid and a base and capable of reacting as either [syn: amphiprotic] [ant: acidic, alkaline]

User Contributed Dictionary

English

Etymology

(ampho), both

Adjective

  1. Having the characteristics of both an acid and a base, and capable of reacting as either; amphiprotic.

Translations

Extensive Definition

In chemistry, an amphoteric substance is one that can react as either an acid or base. The word is derived from the Greek prefix ampho- (αμφί-) which means both and the suffix -ic (-ικός) which means the attribute that the given substance has to react either as acid or as base.

Examples

Examples include amino acids, proteins, and water. Many metals (such as zinc, tin, lead, aluminium, and beryllium) and most metalloids have amphoteric oxides.
For example, zinc oxide (ZnO) reacts differently depending on the pH of the solution:
In acids: ZnO + 2H+ → Zn2+ + H2O
In bases: ZnO + H2O + 2OH- → [Zn(OH)4]2-
This effect can be used to separate different cations, such as zinc from manganese.
There are many other examples of chemical compounds which are also amphoteric, for the simplest example water:
Base (proton acceptor): H2O + HCl → H3O+ + Cl−
Acid (proton donor): H2O + NH3 → NH4+ + OH−
(It can do both at once: 2H2O → H3O+ + OH−)
Base (neutralizing an acid): Al(OH)3 + 3HCl → AlCl3 + 3H2O
Acid (neutralizing a base): Al(OH)3 + NaOH → Na[Al(OH)4]
Some other examples include:
  • Beryllium hydroxide
    • with Acid: Be(OH)2 + 2HCl → BeCl2 + 2H2O
    • with Base: Be(OH)2 + 2NaOH → Na2Be(OH)4
  • Lead oxide
    • with acid: PbO + 2HCl → PbCl2 + H2O
    • with base: PbO + Ca(OH)2 +H2O → Ca2+[Pb(OH)4]2-
  • Zinc oxide
    • with acid: ZnO + 2HCl → ZnCl2 + H2O
    • with base: ZnO + 2NaOH + H2O → Na22+[Zn(OH)4]2-
Some elements not mentioned that are able to form amphoteric oxides: Si, Ti, V, Fe, Co, Zn, Ge, Zr, Ag, Sn, Au

References

amphoteric in Asturian: Anfóteru
amphoteric in Bosnian: Amfoternost
amphoteric in Bulgarian: Амфотерност
amphoteric in Catalan: Amfòter
amphoteric in Danish: Amfoterisk
amphoteric in German: Ampholyt
amphoteric in Estonian: Amfoteersus
amphoteric in Spanish: Anfoterismo
amphoteric in Basque: Anfoteriko
amphoteric in Persian: آمفوتر
amphoteric in French: Ampholyte
amphoteric in Korean: 양쪽성
amphoteric in Indonesian: Amfoterisme
amphoteric in Italian: Anfotero
amphoteric in Lithuanian: Amfoteriškumas
amphoteric in Hungarian: Amfoter
amphoteric in Dutch: Amfoteer
amphoteric in Norwegian: Amfotær
amphoteric in Norwegian Nynorsk: Amfotær
amphoteric in Polish: Amfoteryczność
amphoteric in Russian: Амфотерность
amphoteric in Finnish: Amfolyytti
amphoteric in Swedish: Amfolyt
amphoteric in Turkish: Amfoter
amphoteric in Chinese: 兩性 (化學)
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