Breathe out on a cold winter day and you'll make a fog. Fog is formed whenever warm, wet air (such as your breath) hits colder air (such as the outside air on a chilly day). Presto - out come trillions of tiny drops of water. Fog is simply a low cloud, a wet blanket you can see.

Compound

When 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.

2Na(s) + 2H₂0(l) = 2Na⁺(aq) + 2OH^-(aq) + H₂(g)

This 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.

3Fe(s)+4H₂O(g) = Fe₃O₄(s)+4H₂(g)

Noble metals such as gold and silver do not react with water at all. ¡@

Ammonia

The combustion of ammonia proceeds with difficulty but yields nitrogen gas and water.

4NH₃ + 30₂ + heat = 2N₂ + 6H₂O

Ammonia readily dissolves in water with the liberation of heat.

NH₃ + H₂0 NH₄ ⁺ + OH^-

These 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.

Oxyacids and their salts

Nitric 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).

4HNO₃ + light (or heat) = 4NO₂ + 2H₂O + O₂

Consequently, 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.,

S+ 6HNO₃ = H₂SO₄+ 6HO₂ + 2H₂O