Sodium oxide

Sodium oxide
IUPAC name Sodium oxide
Other names Disodium oxide
Identifiers
CAS number	Y
PubChem
EC number
UN number	1825
Jmol-3D images	Image 1
SMILES [O-2].[Na+].[Na+]
InChI InChI=1S/2Na.O/q2*+1;-2
Properties
Molecular formula	Na2O
Molar mass	61.98 g mol−1
Appearance	white solid
Density	2.27 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
Sublimation conditions	sublimates at 1275 °C
Solubility in water	reacts violently to form NaOH
Solubility	reacts with ethanol
Structure
Crystal structure	Antifluorite (face centered cubic), cF12
Space group	Fm3m, No. 225
Coordination geometry	Tetrahedral (Na+); cubic (O2–)
Thermochemistry
Specific heat capacity C	72.95 J/mol·K
Std molar entropy So298	73 J/mol·K[1]
Std enthalpy of formation ΔfHo298	-416 kJ/mol[1]
Gibbs free energy ΔG	-377.1 kJ/mol
Hazards
MSDS	ICSC 1653
GHS pictograms	[2]
GHS hazard statements	H314[2]
GHS precautionary statements	P280[2]
EU Index	not listed
EU classification	C
R-phrases	R14, R8, R34, R35
S-phrases	(S1/2), S8, S26, S27, S36/37/39, S43, S45
Main hazards	corrosive, reacts violently with water
NFPA 704	0 2 1 OX
Flash point	non-flammable
Related compounds
Other anions	Sodium sulfide Sodium selenide Sodium telluride
Other cations	Lithium oxide Potassium oxide Rubidium oxide Caesium oxide
Related sodium oxides	Sodium peroxide Sodium superoxide
Related compounds	Sodium hydroxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Y   Y/N?)

Sodium oxide (SOX) is a chemical compound with the formula Na₂O. It is used in ceramics and glasses, though not in a raw form. It is the base anhydride of sodium hydroxide, so when water is added to sodium oxide NaOH is produced.

Na₂O + H₂O → 2 NaOH

The 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]

Preparation

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

Na₂O₂ + 2 Na → 2 Na₂O

2 NaNO₂ + 6 Na → 4 Na₂O + N₂

Most of these reactions rely on the reduction of something by sodium, whether it is hydroxide, peroxide, or nitrite.

Burning sodium in air will produce Na₂O and about 20% sodium peroxide Na₂O₂.

6 Na + 2 O₂ → 2 Na₂O + Na₂O₂

Alternatively, sodium carbonate can be heated to 851 °C, producing carbon dioxide and sodium oxide.

Na₂CO₃ → Na₂O + CO₂

Applications

Glass making

Sodium oxide is a significant component of glasses and windows although it is added in the form of "soda" (sodium carbonate). Sodium oxide does not explicitly exist in glasses, since glasses are complex cross-linked polymers. Typically, 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 melts. Soda glass has a much lower melting temperature than pure silica, and has slightly higher elasticity. These changes arise because the silicon dioxide and soda react to form sodium silicates of the general formula Na₂[SiO₂]_x[SiO₃].

Na₂CO₃ → Na₂O + CO₂

Na₂O + SiO₂ → Na₂SiO₃

References

External links

• Sodium oxide information at Webelements.
• External MSDS Data Sheet.