Sodium oxide
chemical compound
Sodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses. It is a white solid. However, the compound itself is rarely encountered and instead, the name "sodium oxide" is used to describe components of various materials such as glasses and fertilizers which contain oxides that include sodium and other elements.
Structure
The structure of sodium oxide has been determined by X-ray crystallography. Most alkali metal oxides M2O (M = Li, Na, K, Rb) crystallise in the antifluorite structure. In this motif the positions of the anions and cations are reversed relative to their positions in CaF2, with sodium ions tetrahedrally coordinated to 4 oxide ions and oxide cubically coordinated to 8 sodium ions.
Preparation
Sodium oxide is produced by the reaction of sodium with sodium hydroxide, sodium peroxide, or sodium nitrite:
2 NaOH + 2 Na → 2 Na2O + H2
To the extent that NaOH is contaminated with water, correspondingly greater amounts of sodium are employed. Excess sodium is distilled from the crude product.
A second method involves heating a mixture of sodium azide and sodium nitrate:
5 NaN3 + NaNO3 → 3 Na2O + 8 N2
Burning sodium in air produces a mixture of Na2O and sodium peroxide (Na2O2):
4 Na + O2 → 2Na2O
and
2 Na + O2 → Na2O2
A third, much less common, method involves a single displacement reaction when heating sodium metal with iron(III) oxide (rust):
6 Na + Fe2O3 → 3 Na2O + 2 Fe
the reaction is done in an inert atmosphere to avoid the reaction of sodium with the air instead.
Applications
Glassmaking
Glasses are often described in terms of their sodium oxide content although they do not really contain Na2O. Furthermore, such glasses are not made from sodium oxide, but the equivalent of Na2O is added in the form of "soda" (sodium carbonate), which loses carbon dioxide at high temperatures:
Na2CO3 → Na2O + CO2
Na2O + SiO2 → Na2SiO3
Na2CO3 + SiO2 → Na2SiO3 + CO2
A typical manufactured glass contains around 15% sodium oxide, 70% silica (silicon dioxide), and 9% lime (calcium oxide).
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