Amphoteric nature of water - acid base characteristics

Water is a weak electrolyte and therefore it does not dissociate easily such as strong acid or base. Water molecule ionizes to a small extent to give hydronium ion (H3O+ and OH-) ion.

Therefore pure water also have small amount of ions. So pure water has a small but measurable electrical conductivity (a current can flow in water due to existing of ions).

Amphoteric behavior of water

Amphoteric behavior means, a compound can act as an acid and base. According to the "Lowry bronsted concept"

  • Acid - loses a proton (H+)
  • Bases - accepts a proton

Now we know pure water also have H3O+ and OH- ions.

Amphoteric metals, compounds and behavior

Water and acid reaction

Now we consider, behavior of HCl and H2S with H2O. Water molecule accepts a proton from HCl and hydronium ion is formed as the result.

Water and HCl

Hydrochloric acid (HCl) is a strong acid and dissolve very well in water. One electron pair of oxygen atom of water molecule attacks H atom in the HCl molecule because that H atom is positively polarized. So HCl dissociates completely by giving H3O+ ion and Cl- ion. In this example water molecule behave as a base.

HCl and water reaction

Water and hydrogen sulfide

hydrogen sulfide and water reaction

Water and bases reaction

Water molecule donate a proton to the base to form hydroxyl ion.

Water and ammonia reaction

Ammonia takes a proton from water molecule and forms ammonium ion (NH4+) and hydroxyl ion (OH-).

ammonia and water reaction

Why is water amphoteric

Water is a polar covalent compound. It dissociate slightly in water to H+ and OH- ions. Due to exist of H+ ion, it shows acidic characteristics. Also due to exist of OH- ion, it can take H+ ions to show basic characteristics.

What do you understand by amphoteric nature of water

Water can react with both acids and bases like other amphoteric elements and compounds.

Related tutorials for amphoteric behavior of water

Amphoteric metals, compounds and behavior What are the acids and bases Identify ammonia and ammonium salts Testing ammonia gas