Posted by ROSHAN B.S on Aug. 23, 2014, 10:15 p.m.
Although nearly 99% sulfuric acid can be made, the subsequent loss of SO
3 at the boiling point brings the concentration to 98.3% acid. The 98% grade is more stable in storage, and is the usual form of what is described as "concentrated sulfuric acid." Other concentrations are used for different purposes. Some common concentrations are:[9][10]
| Mass fraction H2SO4 | Density (kg/L) | Concentration (mol/L) | Common name |
|---|---|---|---|
| 10% | 1.07 | ~1 | dilute sulfuric acid |
| 29–32% | 1.25–1.28 | 4.2–5 | battery acid (used in lead–acid batteries) |
| 62–70% | 1.52–1.60 | 9.6–11.5 | chamber acid fertilizer acid |
| 78–80% | 1.70–1.73 | 13.5–14 | tower acid Glover acid |
| 98% | 1.83 | ~18 | concentrated sulfuric acid |
"Chamber acid" and "tower acid" were the two concentrations of sulfuric acid produced by the lead chamber process, chamber acid being the acid produced in lead chamber itself (<70% to avoid contamination with nitrosylsulfuric acid) and tower acid being the acid recovered from the bottom of the Glover tower.[9][10] They are now obsolete as commercial concentrations of sulfuric acid, although they may be prepared in the laboratory from concentrated sulfuric acid if needed. In particular, "10M" sulfuric acid (the modern equivalent of chamber acid, used in many titrations) is prepared by slowly adding 98% sulfuric acid to an equal volume of water, with good stirring: the temperature of the mixture can rise to 80 °C (176 °F) or higher.[10]
Sulfuric acid reacts with its anhydride, SO
3, to form H
2S
2O
7, called pyrosulfuric acid, fuming sulfuric acid, Disulfuric acid or oleumor, less commonly, Nordhausen acid. Concentrations of oleum are either expressed in terms of % SO
3 (called % oleum) or as %H
2SO
4 (the amount made if H
2O were added); common concentrations are 40% oleum (109% H
2SO
4) and 65% oleum (114.6%H
2SO
4). Pure H
2S
2O
7 is a solid with melting point 36 °C.
Pure sulfuric acid has a vapor pressure of <0.001 torr at 25 °C and 1 torr at 145.8 °C,[11] and 98% sulfuric acid has a <1 mmHg vapor pressure at 40 °C.[12]