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Copper iodide

Copper(I) iodide
Copper(I) iodide
Names
IUPAC name
Copper(I) iodide
Other names
Cuprous iodide
Identifiers
3D model (Jmol)
ChemSpider
ECHA InfoCard 100.028.795
PubChem CID
Properties
CuI
Molar mass 190.45 g/mol
Appearance White powder
when impure: tan or brownish
Odor odorless
Density 5.67 g/cm3
Melting point 606 °C (1,123 °F; 879 K)
Boiling point 1,290 °C (2,350 °F; 1,560 K) (decomposes)
0.0042 g/100 mL
1 x 10−12
Solubility soluble in ammonia and potassium solutions
insoluble in dilute acids
Vapor pressure 10 mm Hg (656 °C)
-63.0·10−6 cm3/mol
2.346
Structure
zincblende
Tetrahedral anions and cations
Hazards
Safety data sheet Sigma Aldrich
GHS pictograms GHS-pictogram-exclam.svgGHS-pictogram-pollu.svg
H302, H315, H319, H335, H400, H410
P261, P273, P305+351+338, P501
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
US health exposure limits (NIOSH):
PEL (Permissible)
TWA 1 mg/m3 (as Cu)
REL (Recommended)
TWA 1 mg/m3 (as Cu)
IDLH (Immediate danger)
TWA 100 mg/m3 (as Cu)
Related compounds
Other anions
Copper(I) fluoride
Copper(I) chloride
Copper(I) bromide
Other cations
silver(I) iodide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
YesY  (what is YesYN ?)
Infobox references

Copper(I) iodide is the inorganic compound with the formula CuI. It is also known as cuprous iodide. It is useful in a variety of applications ranging from organic synthesis to cloud seeding.

Pure copper(I) iodide is white, but samples are often tan or even, when found in nature as rare mineral marshite, reddish brown, but such color is due to the presence of impurities. It is common for samples of iodide-containing compounds to become discolored due to the facile aerobic oxidation of the iodide anion to molecular iodine.

Copper(I) iodide, like most "binary" (containing only two elements) metal halides, is an inorganic polymer. It has a rich phase diagram, meaning that it exists in several crystalline forms. It adopts a zinc blende structure below 390 °C (γ-CuI), a wurtzite structure between 390 and 440 °C (β-CuI), and a rock salt structure above 440 °C (α-CuI). The ions are tetrahedrally coordinated when in the zinc blende or the wurtzite structure, with a Cu-I distance of 2.338 Å. Copper(I) bromide and copper(I) chloride also transform from the zinc blende structure to the wurtzite structure at 405 and 435 °C, respectively. Therefore, the longer the copper – halide bond length, the lower the temperature needs to be to change the structure from the zinc blende structure to the wurtzite structure. The interatomic distances in copper(I) bromide and copper(I) chloride are 2.173 and 2.051 Å, respectively.

Copper(I) iodide can be prepared by heating iodine and copper in concentrated hydriodic acid, HI. In the laboratory however, copper(I) iodide is prepared by simply mixing an aqueous solution of sodium or potassium iodide and a soluble copper(II) salt such copper sulfate.

The CuI2 immediately decomposes to iodine and insoluble copper(I) iodide, releasing I2.

This reaction has been employed as a means of assaying copper(II) samples, since the evolved I2 can be analyzed by redox titration. The reaction in itself may look rather odd, as using the rule of thumb for a proceeding redox reaction, Eooxidator − Eoreductor > 0, this reaction fails. The quantity is below zero, so the reaction should not proceed. But the equilibrium constant for the reaction is 1.38*10−13. By using fairly moderate concentrates of 0.1 mol/L for both iodide and Cu2+, the concentration of Cu+ is calculated as 3*10−7. As a consequence, the product of the concentrations is far in excess of the solubility product, so copper(I)iodide precipitates. The process of precipitation lowers the copper(I) concentration, providing an entropic driving force according to Le Chatelier's principle, and allowing the redox reaction to proceed.


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