OXIDES AND WATER 71OXIDES AND WATER
Nearly all the elements are capable of combining with oxygen
to form oxides. All the oxides have a greater or less tendency
to combine with water or with other oxides. In general the oxides
of metals combine with water to form bases, and the oxides of non-
metals combine with water to form acids.- Sodium Oxide and Water. Support a porcelain cru-
cible cover on a triangle and heat it to redness; while it is
thus hot, place upon it, by means of iron pincers, a piece of
sodium the size of a small pea. Remove the burner and let
the sodium burn. When cold dissolve the white oxide in a few
cubic centimeters of water and test the solution with litmus.
Notice some effervescence when the oxide is dissolving. Note
that the solution turns litmus blue and feels very slippery
when rubbed between the fingers.
When sodium burns in an abundance of air an oxide of the
formula Na 2 O 2 and called sodium peroxide is formed. When
sodium peroxide is treated with water it reacts according to the
equation
2Na 2 O 2 + 2H 2 O -> 4NaOH + O 2
thus losing one-half of its oxygen and yielding soluble sodium
hydroxide. If the peroxide is heated with sodium out of contact
with the air sodium oxide, Na20, is formed. This compound
has half as much oxygen to a given weight of sodium as the per-
oxide. Sodium oxide reacts with water to form sodium hydroxide
without the liberation of oxygen.
Na 2 O + H 2 0 -> 2NaOHSodium hydroxide, NaOH, is very soluble in water; it is one of the
strongest bases.- Calcium Oxide and Water. The well-known sub-
stance " quicklime " is calcium oxide. Calcium oxide could be
made by burning bits of calcium, but the oxide quickly coats
over the surface of the metal, and it is difficult to make the
interior portions of the lump react. For this experiment
take a lump of quicklime out of a recently opened container.
Cover it with water in a porcelain dish and then pour off the
excess of water that did not soak into the porous lump. Note