Disulfuric acid
| Disulfuric acid | |
|---|---|
| |
| IUPAC name | Disulfuric acid |
| Other names | Pyrosulfuric acid |
| Identifiers | |
| InChI | InChI=1/H2O7S2/c1-8(2,3)7-9(4,5)6/h(H,1,2,3)(H,4,5,6) |
| InChIKey | VFNGKCDDZUSWLR-UHFFFAOYAZ |
| Standard InChI | InChI=1S/H2O7S2/c1-8(2,3)7-9(4,5)6/h(H,1,2,3)(H,4,5,6) |
| Standard InChIKey | VFNGKCDDZUSWLR-UHFFFAOYSA-N |
| CAS number | [] |
| EC number | |
| ChemSpider | |
| Properties[1] | |
| Chemical formula | H2S2O7 |
| Molar mass | 178.14 g/mol |
| Appearance | colourless solid, very hygroscopic |
| Density | 1.9 g/cm3, solid (20 ºC) |
| Melting point |
35 °C |
| Boiling point |
decomp. |
| Solubility in water | reacts violently |
| Solubility in ethanol | reacts |
| Hazards[2] | |
| Material safety data sheet (MSDS) | ICSC |
| EU index number | 016-019-00-2 |
| GHS pictograms |  
|
| GHS signal word | DANGER |
| GHS hazard statements | H314, H335 |
| Flash point | non-flammable |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) | |
Disulfuric acid is a sulfur oxoacid. It is a major constituent of fuming sulfuric acid, oleum, and also a minor constituent of liquid anhydrous sulfuric acid (approx. 3.6 mmol/kg H2S2O7 and 4.4 mmol/kg HS2O7− at 25 ºC) due ionic self-dehydration:[3]
- 2H2SO4 ⇌ H3O+ + HS2O7−
- K (25 ºC) = 5.1 × 10−5
The acid is prepared by reacting excess sulfur trioxide with sulfuric acid:
- H2SO4 + SO3 → H2S2O7
Disulfuric acid is a strong acid and protonates sulfuric acid in the (anhydrous) sulfuric acid solvent system.[3]
- Ka (25 ºC, H2SO4) = [H3SO4+][HS2O7−]/[H2S2O7] = 1.4 × 10−2
There are salts of disulfuric acid, commonly called disulfates or pyrosulfates, e.g. potassium disulfate, K2S2O7. The disulfate ion, S2O72−, is a pair of corner-sharing SO4 tetrahedra, with S–Oµ–S = 124º, S–Oµ = 164.5 pm and S–Ot = 144 pm.
There are other related acids with the general formula H2O·(SO3)x though none are isolable. The trisulfate ion, S3O102−, and the pentasulfate ion, S5O162−, have been crystallographically characterised: the central sulfur atoms have tetrahedral coordination, with corner-sharing SO4 tetrahedra, but the terminal SO3 groups are almost planar, as in sulfur trioxide.[3]
References
- ↑ CRC Handbook of Chemistry and Physics, 62nd ed.; Weast, Robert C., Ed.; CRC Press: Boca Raton, FL, 1981; p B-154. ISBN 0-8493-0462-8.
- ↑ Index no. 016-019-00-2 of Annex VI, Part 3, to Regulation (EC) No 1272/2008 of the European Parliament and of the Council of 16 December 2008 on classification, labelling and packaging of substances and mixtures, amending and repealing Directives 67/548/EEC and 1999/45/EC, and amending Regulation (EC) No 1907/2006. OJEU L353, 31.12.2008, pp 1–1355 at p 400.
- ↑ 3.0 3.1 3.2 Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; pp 843, 845. ISBN 0-08-022057-6.
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