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Chromic acid

Chromic acid
Dichromic acid
Structural formulae of dichromic acid (left) and chromic acid (right)
Dichromic acid (left) and chromic acid (right)
Names
IUPAC names
Chromic acid
Dichromic acid
Systematic IUPAC name
Dihydroxidodioxidochromium
Other names
Chromic(VI) acid
Tetraoxochromic acid
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.028.910 Edit this at Wikidata
EC Number
  • 231-801-5
25982
UNII
UN number 1755 1463
  • InChI=1S/Cr.2H2O.2O/h;2*1H2;;/q+2;;;;/p-2 checkY
    Key: KRVSOGSZCMJSLX-UHFFFAOYSA-L checkY
  • InChI=1/Cr.2H2O.2O/h;2*1H2;;/q+2;;;;/p-2/rCrH2O4/c2-1(3,4)5/h2-3H
    Key: KRVSOGSZCMJSLX-OOUCQFSRAZ
  • O[Cr](O)(=O)=O
  • O=[Cr](=O)(O)O
Properties
H2CrO4 (chromic acid)
H2Cr2O7 (dichromic acid)
Molar mass 118.008 g/mol (chromic acid)
218.001 g/mol (dichromic acid)
Appearance Dark purplish-red sand-like crystalline solid or powder[clarification needed]
Odor Odorless
Density 1.201 g/cm3[clarification needed]
Melting point 197 °C (387 °F; 470 K) [clarification needed]
Boiling point 250 °C (482 °F; 523 K) (decomposes)[clarification needed]
169 g/(100 mL)[clarification needed]
Acidity (pKa) −0.8 to 1.6 (chromic acid)
Conjugate base Chromate and dichromate
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 highly toxic, carcinogen, corrosive
GHS labelling:
GHS03: OxidizingGHS05: CorrosiveGHS06: ToxicGHS07: Exclamation markGHS08: Health hazardGHS09: Environmental hazard
Danger
H271, H300+H310+H330, H301, H314, H317, H334, H340, H341, H350, H361, H372, H410
P201, P202, P210, P220, P221, P260, P261, P262, P264, P270, P271, P272, P273, P280, P281, P283, P284, P285, P301+P310, P301+P330+P331, P302+P350, P302+P352, P303+P361+P353, P304+P340, P304+P341, P305+P351+P338, P306+P360, P308+P313, P310, P314, P320, P321, P322, P330, P333+P313, P342+P311, P361, P363, P370+P378, P371+P380+P375, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 0: Will not burn. E.g. waterInstability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazard COR: Corrosive; strong acid or base. E.g. sulfuric acid, potassium hydroxide
4
0
1
COR
Lethal dose or concentration (LD, LC):
51.9 mg/kg (H2CrO4·2Na, rat, oral)[2]
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 0.005 mg/m3[1]
REL (Recommended)
 TWA 0.001 mg Cr(VI)/m3[1]
IDLH (Immediate danger)
 15 mg Cr(VI)/m3[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Chromic acid is jargon for a solution formed by the addition of sulfuric acid to aqueous solutions of dichromate. It consists at least in part of chromium trioxide.[3]

The term chromic acid is usually used for a mixture made by adding concentrated sulfuric acid to a dichromate, which may contain a variety of compounds, including solid chromium trioxide. This kind of chromic acid may be used as a cleaning mixture for glass. Chromic acid may also refer to the molecular species, H2CrO4 of which the trioxide is the anhydride. Chromic acid features chromium in an oxidation state of +6 (and a valence of VI or 6). It is a strong and corrosive oxidising agent and a moderate carcinogen.

  1. ^ a b c NIOSH Pocket Guide to Chemical Hazards. "#0138". National Institute for Occupational Safety and Health (NIOSH).
  2. ^ "Chromic acid and chromates". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  3. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.

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