Sodium pyrosulfate

Sodium pyrosulfate

Names
IUPAC name Disodium disulfate
Other names Disulfuric acid disodium salt Sodium disulfate Sodium pyrosulphate
Identifiers
Jmol-3D images	Image
SMILES [Na+].[Na+].[O-]S(=O)(=O)OS(=O)(=O)[O-]
Properties
Chemical formula	Na2S2O7
Molar mass	222.12 g/mol
Appearance	White crystalline solid
Density	2.658 g/cm3
Melting point	400.9 °C (753.6 °F; 674.0 K)
Boiling point	460 °C (860 °F; 733 K) (decomposition)
Solubility in water	Hydrolyzes
Thermochemistry
Std enthalpy of formation (ΔfHo298)	-1,717.6--1,907 kJ/mol
Hazards
Safety data sheet	None
Flash point	Non-flammable
Related compounds
Related compounds	Sodium bisulfate Sodium metabisulfite Sodium persulfate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Sodium pyrosulfate (also known as disodium disulfate) is a sodium salt of disulfuric acid, with the formula Na₂S₂O₇.

Properties

Chemical

Sodium pyrosulfate decomposes when heated above 460 °C to give sodium sulfate and sulfur trioxide:

Na₂S₂O₇ → Na₂SO₄ + SO₃

This reaction is a convenient way of obtaining sulfur trioxide, as it does not require complex installation and the pyrosulfate precursor, sodium bisulfate, is readily available.

Sodium pyrosulfate hydrolyzes in water to sulfuric acid.

Physical

Sodium disulfate is a white salt, soluble in water.

Availability

Sodium pyrosulfate is rarely available from suppliers. Sigmaaldrich used to sell sodium disulfate fused with sodium bisulfate.

Preparation

Sodium pyrosulfate can be easily made by heating sodium bisulfate at temperatures between 200-400 °C:

2 NaHSO₄ → Na₂S₂O₇ + H₂O

However, other authors indicate different temperature decomposition ranges.

Projects

• Make sulfur trioxide
• Make ammonium pyrosulfate

Handling

Safety

Sodium pyrosulfate rapidly hydrolyzes in contact with water, releasing sulfuric acid, which is corrosive.

Storage

In closed bottles, away from any moisture.

Disposal

Add it in large amounts of water to hydrolyze it, then carefully neutralize the acid with a base.

References

Relevant Sciencemadness threads

• oleum & SO3