an active metal such as sodium is placed in contact with liquid
water, a violent exothermic (heat-producing) reaction occurs that
releases flaming hydrogen gas.
+ 2H20(l) = 2Na+(aq)
+ 2OH-(aq) + H2(g)
is an example of an oxidation-reduction reaction, which a reaction
in which electrons are transferred from one atom to another. In
this case, electrons are transferred from sodium atoms (forming
Na+ ions) to water molecules to produce hydrogen gas and OH- ions.
The other alkali metals give similar reactions with water. Less
active metals react slowly with water. For example, iron reacts
at a negligible rate with liquid water but reacts much more rapidly
with superheated steam to form iron oxide and hydrogen gas.
metals such as gold and silver do not react with water at all. ¡@
combustion of ammonia proceeds with difficulty but yields nitrogen
gas and water.
+ 302 + heat =
readily dissolves in water with the liberation of heat.
+ H20 NH4 + + OH-
aqueous solutions of ammonia are basic and are sometimes called
solutions of ammonium hydroxide (NH40H). The equilibrium,
however, is such that a 1.0 molar solution of NH3 provides only
4.2 millimoles of hydroxide ion. The hydrates NH3¡DH20,
2NH3¡DH20, and NH3¡D2H20
exist and have been shown to consist of ammonia and water molecules
linked by intermolecular hydrogen bonds. Liquid ammonia is used
extensively as a nonaqueous solvent. The alkali metals as well as
the heavier alkaline earth metals and even some inner transition
metals dissolve in liquid ammonia, producing blue solutions. Physical
measurements, including electrical conductivity studies, provide
evidence that this blue colour and electrical current are due to
the solvated electron.
and their salts
acid, HNO3, was known to the alchemists of the 8th century
as "aqua fortis" (strong water). It is formed by the nitrogen
dioxide (NO2) with water.
When pure, nitic acid is a colourless liquid that boils at 86º
C and freezes at -42º C. Upon being exposed to light or heat,
it decomposes to produce oxygen, water, and a mixture of nitrogen
oxides (primarily NO2).
+ light (or heat) =
4NO2 + 2H2O + O2
nitric acid is often yellow or brown in colour because of the NO2
that forms as it decomposes. Nitric acid is stable in aqueous solution,
and 68% solutions of the acid (i.e, 68 grams of HNO3 per 100 grams
of solution) are sold as concentrated HNO3. It is both a strong
oxidizing agent and a strong acid. Nonmetallic elements such as
carbon (C), iodine (I), phosphorus (P), and sulfur (S) are oxidized
by concentrated HNO3 to their oxides or oxyacids with the formation
of NO2: e.g.,
6HNO3 = H2SO4+
6HO2 + 2H2O