Sodium oxide

Sodium oxide

Names
IUPAC name Sodium oxide
Other names Disodium oxide Natrium oxide (historic) Soda Sodium oxidosodium
Identifiers
CAS Number	1313-59-3 Y
3D model (JSmol)	Interactive image
ECHA InfoCard	100.013.827
EC Number	215-208-9
PubChem CID	73971
UNII	3075U8R23D Y
UN number	1825
CompTox Dashboard (EPA)	DTXSID0049781
InChI InChI=1S/2Na.O/q2*+1;-2
SMILES [O-2].[Na+].[Na+]
Properties
Chemical formula	Na2O
Molar mass	61.979 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 to form NaOH
Solubility	Reacts with ethanol
Magnetic susceptibility (χ)	−19.8·10−6 cm3/mol
Structure
Crystal structure	Antifluorite (face centered cubic), cF12
Space group	Fm3m, No. 225
Coordination geometry	Tetrahedral (Na+); cubic (O2−)
Thermochemistry
Heat capacity (C)	72.95 J/(mol·K)
Std molar entropy (S⦵298)	73 J/(mol·K)[1]
Std enthalpy of formation (ΔfH⦵298)	−416 kJ/mol[1]
Gibbs free energy (ΔfG⦵)	−377.1 kJ/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	corrosive, reacts violently with water
GHS labelling:
Pictograms	[2]
Hazard statements	H314
Precautionary statements	P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P405, P501
NFPA 704 (fire diamond)	3 0 1 W
Flash point	nonflammable
Safety data sheet (SDS)	ICSC 1653
Related compounds
Other anions	Sodium sulfide Sodium selenide Sodium telluride Sodium polonide
Other cations	Lithium oxide Potassium oxide Rubidium oxide Caesium oxide
Related sodium oxides	Sodium peroxide Sodium superoxide Sodium ozonide
Related compounds	Sodium hydroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

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.

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.^[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

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).

A third much less known method involves 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.

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). 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.

Reactions

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").

References

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