Editing Sulfuric acid (section)

== Physical properties ==

===Grades of sulfuric acid===
Although nearly 100% sulfuric acid solutions can be made, the subsequent loss of [[sulfur trioxide|{{chem2|SO3}}]] at the boiling point brings the concentration to 98.3% acid. The 98.3% grade, which is more stable in storage, is the usual form of what is described as "concentrated sulfuric acid". Other concentrations are used for different purposes. Some common concentrations are:<ref name="Columbia">{{cite book |chapter=Sulfuric Acid|chapter-url=http://www.encyclopedia.com/topic/sulfuric_acid.aspx|title=The Columbia Encyclopedia |edition=6th |year=2009 |access-date=16 March 2010}}</ref><ref name="EB11">{{cite book|chapter=Sulphuric acid|title=Encyclopædia Britannica|edition=11th|year=1910–1911|volume=26|pages=65–69|title-link=Encyclopædia Britannica Eleventh Edition}} Please note, no EB1911 wikilink is available to this article</ref>
{| class="wikitable"
|-
! Mass fraction<br />{{chem2|H2SO4}}
! Density<br />(kg/L)
! Concentration<br />(mol/L)
! Common name
|-
| <29% || 1.00–1.25 || align=center| <4.2 || diluted sulfuric acid
|-
| 29–32% || 1.25–1.28 || align=center| 4.2–5.0 || battery acid<br />(used in [[lead–acid batteries]])
|-
| 62–70% || 1.52–1.60 || align=center| 9.6–11.5 || chamber acid<br />fertilizer acid
|-
| 78–80% || 1.70–1.73 || align=center| 13.5–14.0 || tower acid<br />Glover acid
|-
| 93.2% || 1.83 || align=center| 17.4 || 66 [[Baumé scale|°Bé]] ("66-degree Baumé") acid
|-
| 98.3% || 1.84 || align=center| 18.4 || 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 the lead chamber itself (<70% to avoid contamination with [[nitrosylsulfuric acid]]) and tower acid being the acid recovered from the bottom of the Glover tower.<ref name="Columbia"/><ref name="EB11"/> 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, "10 M" sulfuric acid (the modern equivalent of chamber acid, used in many [[titration]]s), 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&nbsp;°C (176&nbsp;°F) or higher.<ref name="EB11"/>

===Sulfuric acid===
Sulfuric acid contains not only {{chem2|H2SO4}} molecules, but is actually an equilibrium of many other chemical species, as it is shown in the table below.
{| class="wikitable sortable"
|+colspan=2|Equilibrium of pure sulfuric acid<ref name="greenwood"/>
!Species
!mMol/kg
|-
|{{chem2|HSO4-}}
| 15.0
|-
|{{chem2|H3SO4+}}
| 11.3
|-
|{{chem2|H3O+}}
| 8.0
|-
|{{chem2|HS2O7-}}
| 4.4
|-
|{{chem2|H2S2O7}}
| 3.6
|-
|{{chem2|H2O}}
| 0.1
|}
Sulfuric acid is a colorless oily liquid, and has a vapor pressure of <0.001 mmHg at 25&nbsp;°C and 1 mmHg at 145.8&nbsp;°C,<ref name="OEHHA">{{cite book |chapter=Sulfuric acid|chapter-url=http://oehha.ca.gov/air/chronic_rels/pdf/sulfuric.pdf|title=Determination of Noncancer Chronic Reference Exposure Levels Batch 2B December 2001|year=2001|archive-url=https://web.archive.org/web/20030522222447/http://oehha.ca.gov/air/chronic_rels/pdf/sulfuric.pdf|access-date=1 October 2012|archive-date=22 May 2003}}</ref> and 98% sulfuric acid has a vapor pressure of <1 mmHg at 40&nbsp;°C.<ref name="Rhodia">{{cite web|url=http://www.rhodia.com/our_company/businesses/documents/Sulfuric_Acid_98.pdf|archive-url=https://web.archive.org/web/20110107022427/http://www.rhodia.com/our_company/businesses/documents/Sulfuric_Acid_98.pdf|url-status=dead|archive-date=7 January 2011|title=Sulfuric Acid 98%|year=2009|access-date=2 July 2014|publisher=rhodia.com}}</ref>

In the solid state, sulfuric acid is a molecular solid that forms [[Monoclinic crystal system|monoclinic crystals]] with nearly trigonal lattice parameters. The structure consists of layers parallel to the (010) plane, in which each molecule is connected by [[hydrogen bond]]s to two others.<ref name="kemnitz"/> [[Hydrate]]s {{chem2|H2SO4*''n''H2O}} are known for ''n'' = 1, 2, 3, 4, 6.5, and 8, although most intermediate hydrates are stable against [[disproportionation]].<ref>{{cite journal |last1=Giauque |first1=W. F. |last2=Hornung |first2=E. W. |last3=Kunzler |first3=J. E. |last4=Rubin |first4=T. R. |title=The Thermodynamic Properties of Aqueous Sulfuric Acid Solutions and Hydrates from 15 to 300K. 1 |journal=Journal of the American Chemical Society |date=January 1960 |volume=82 |issue=1 |pages=62–70 |doi=10.1021/ja01486a014|bibcode=1960JAChS..82...62G }}</ref>

===Polarity and conductivity===

[[Anhydrous]] {{chem2|H2SO4}} is a very [[chemical polarity|polar]] liquid, having a [[Relative permittivity|dielectric constant]] of around 100. It has a high [[Electrical resistivity and conductivity|electrical conductivity]], a consequence of [[autoprotolysis]], i.e. self-[[protonation]]:<ref name=greenwood>{{Greenwood&Earnshaw2nd}}</ref>
:{{chem2 |2 H2SO4 <-> H3SO4+ + HSO4- }}
The [[equilibrium constant]] for autoprotolysis (25&nbsp;°C) is:<ref name=greenwood/>
:{{chem2|[H3SO4]+[HSO4]-}} =  2.7 × 10<sup>−4</sup>

The corresponding [[Self-ionization of water|equilibrium constant for water]], ''K''<sub>w</sub> is 10<sup>−14</sup>, a factor of 10<sup>10</sup> (10 billion) smaller.

In spite of the viscosity of the acid, the effective [[molar conductivity|conductivities]] of the {{chem2|H3SO4+}} and {{chem2|HSO4-}} ions are high due to an intramolecular proton-switch mechanism (analogous to the [[Grotthuss mechanism]] in water), making sulfuric acid a good conductor of electricity. It is also an excellent solvent for many reactions.