Sodium oxide
Names IUPAC name Other names Identifiers ChemSpider ECHA InfoCard 100.013.827 EC Number UNII UN number 1825 Properties Na2O Molar mass 61.979 g·mol−1 Appearance white solid Density 2.49 g/cm3 Melting point 1,132 °C (2,070 °F; 1,405 K) Boiling point 1,950 °C (3,540 °F; 2,220 K) sublimates sublimates at 1275 °C Reacts to form NaOH Solubility Reacts with ethanol −19.8·10−6 cm3/mol Structure Antifluorite (face centered cubic), cF12 Fm3m, No. 225 Tetrahedral (Na+); cubic (O2−) Thermochemistry 72.95 J/(mol·K) 73 J/(mol·K)[1] −416 kJ/mol[1] −377.1 kJ/mol Hazards Occupational safety and health (OHS/OSH): corrosive, reacts violently with water GHS labelling: [2] H314 P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P405, P501 NFPA 704 (fire diamond) Flash point nonflammable Safety data sheet (SDS) ICSC 1653 Related compounds Sodium hydroxide
Sodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses. It is a white solid but the compound is rarely encountered. Instead “sodium oxide” is used to describe components of various materials such as glasses and fertilizers which contain oxides that include sodium and other elements. Sodium oxide is a component.
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.[3][4]
Sodium oxide is produced by the reaction of sodium with sodium hydroxide, sodium peroxide, or sodium nitrite:[5]
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.[6]
A second method involves heating a mixture of sodium azide and sodium nitrate:[6]
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 known method involves a single displacement reaction when heating sodium metal with iron(III) oxide (rust):
6 Na + Fe2O3 → 3 Na2O + 2 Fe
the reaction should be done in an inert atmosphere to avoid the reaction of sodium with the air instead.
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). The sodium carbonate “soda” serves as a flux to lower the temperature at which the silica mixture melts. Such soda-lime glass has a much lower melting temperature than pure silica and has slightly higher elasticity. These changes arise because the Na2[SiO2]x[SiO3]-based material is somewhat more flexible.
Sodium oxide reacts readily and irreversibly with water to give sodium hydroxide:
Na2O + H2O → 2 NaOH
Because of this reaction, sodium oxide is sometimes referred to as the base anhydride of sodium hydroxide (more archaically, “anhydride of caustic soda”).
