Ammonium - Acid Base Properties

Acid Base Properties

The ammonium ion is generated when ammonia, a weak base, reacts with Brønsted acids (proton donors):

H+ + NH3 → NH4+

The acid dissociation constant (pKa) of NH4+ is 9.25.

The ammonium ion is mildly acidic, reacting with Brønsted bases to return to the uncharged ammonia molecule:

NH4+ + B- → HB + NH3

Thus, treatment of concentrated solutions of ammonium salts with strong base gives ammonia. When ammonia is dissolved in water, a tiny amount of it converts to ammonium ions:

H3O+ + NH3 H2O + NH4+

The degree to which ammonia forms the ammonium ion depends on the pH of the solution. If the pH is low, the equilibrium shifts to the right: more ammonia molecules are converted into ammonium ions. If the pH is high (the concentration of hydrogen ions is low), the equilibrium shifts to the left: the hydroxide ion abstracts a proton from the ammonium ion, generating ammonia.

Formation of ammonium compounds can also occur in the vapor phase; for example, when ammonia vapor comes in contact with hydrogen chloride vapor, a white cloud of ammonium chloride forms, which eventually settles out as a solid in a thin white layer on surfaces.

The conversion of ammonium back to ammonia is easily accomplished by the addition of strong base.

Read more about this topic:  Ammonium

Famous quotes containing the words properties and/or base:

    The reason why men enter into society, is the preservation of their property; and the end why they choose and authorize a legislative, is, that there may be laws made, and rules set, as guards and fences to the properties of all the members of the society: to limit the power, and moderate the dominion, of every part and member of the society.
    John Locke (1632–1704)

    Yet herein will I imitate the sun,
    Who doth permit the base contagious clouds
    To smother up his beauty from the world,
    That when he please again to be himself,
    Being wanted, he may be more wondered at
    By breaking through the foul and ugly mists
    Of vapors that did seem to strangle him
    William Shakespeare (1564–1616)