Sodium oxide
A white solid used in glassmaking and ceramics.
Sodium oxide, with the formula Na2O, is a white solid used in ceramics and glasses. However, the pure compound is seldom found; instead, the term "sodium oxide" refers to the sodium-containing oxide components in materials like glasses and fertilizers.
Its structure, determined by X-ray crystallography, follows the antifluorite pattern common to most alkali metal oxides (M2O for M = Li, Na, K, Rb). In this arrangement, the positions of anions and cations are swapped compared to calcium fluoride (CaF2): sodium ions are tetrahedrally coordinated to four oxide ions, while each oxide ion is cubically coordinated to eight sodium ions.
Sodium oxide can be prepared by reacting sodium with sodium hydroxide, sodium peroxide, or sodium nitrite: 2 NaOH + 2 Na → 2 Na2O + H2. If the sodium hydroxide contains water, extra sodium is needed, and excess sodium is distilled from the crude product. Another method heats sodium azide with sodium nitrate: 5 NaN3 + NaNO3 → 3 Na2O + 8 N2. Burning sodium in air yields a mix of Na2O and sodium peroxide (Na2O2) via 4 Na + O2 → 2 Na2O and 2 Na + O2 → Na2O2. A less common route involves a single displacement reaction between sodium metal and iron(III) oxide (rust): 6 Na + Fe2O3 → 3 Na2O + 2 Fe, carried out in an inert atmosphere to prevent sodium reacting with air.
In glassmaking, glasses are often described by their sodium oxide content, though they do not actually contain Na2O. Instead, the equivalent is added as soda (sodium carbonate), which loses carbon dioxide at high temperatures: Na2CO3 → Na2O + CO2, then Na2O + SiO2 → Na2SiO3, or overall Na2CO3 + SiO2 → Na2SiO3 + CO2. A typical manufactured glass contains about 15% sodium oxide, 70% silica, and 9% lime. The soda acts as a flux, lowering the melting temperature of the silica mixture. This soda-lime glass melts at a much lower temperature than pure silica and is slightly more elastic, due to the flexibility of the Na2[SiO2]x[SiO3]-based material.
Sodium oxide reacts readily and irreversibly with water to form sodium hydroxide: Na2O + H2O → 2 NaOH. Because of this, it is sometimes called the base anhydride of sodium hydroxide (or, archaically, "anhydride of caustic soda").
- formula
- Na2O
- appearance
- White solid
- crystal_structure
- Antifluorite structure
- coordination
- Sodium ions tetrahedrally coordinated to 4 oxide ions; oxide cubically coordinated to 8 sodium ions
- key_reaction
- Reacts irreversibly with water to give sodium hydroxide
Lore & Background
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, where the positions of anions and cations are reversed relative to CaF2. Sodium oxide is produced by several methods, including 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, and 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). 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, done in an inert atmosphere to avoid reaction of sodium with air.
Reader's Guide
Sodium oxide is significant primarily for its role in glassmaking, where glasses are often described in terms of their sodium oxide content although they do not really contain Na2O. 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. A typical manufactured glass contains around 15% sodium oxide, 70% silica, and 9% lime. The sodium carbonate serves as a flux to lower the temperature at which the silica mixture melts, producing soda-lime glass with a much lower melting temperature than pure silica and slightly higher elasticity. These changes arise because the Na2[SiO2]x[SiO3]-based material is somewhat more flexible. Sodium oxide also reacts readily and irreversibly with water to give sodium hydroxide, and is sometimes referred to as the base anhydride of sodium hydroxide.
Did You Know?
- Sodium oxide crystallises in the antifluorite structure, where sodium ions are tetrahedrally coordinated to 4 oxide ions and oxide ions are cubically coordinated to 8 sodium ions.
- It can be produced by 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).
- Sodium oxide reacts irreversibly with water to give sodium hydroxide, and is sometimes called the base anhydride of sodium hydroxide.
More in Sodium Compounds 1-24
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