Copper(I) iodide
_iodide.jpg) |
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| Names | |
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IUPAC name
Copper(I) iodide
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| Other names
Cuprous iodide
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| Identifiers | |
7681-65-4 
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| 3D model (Jmol) | Interactive image |
| ChemSpider |
22766
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| ECHA InfoCard | 100.028.795 |
| PubChem | 24350 |
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| 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 | |
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Solubility product (Ksp)
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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 | |
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Refractive index (nD)
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2.346 |
| Structure | |
| zincblende | |
| Tetrahedral anions and cations | |
| Hazards | |
| Safety data sheet | Sigma Aldrich |
| GHS pictograms |
 
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| H302, H315, H319, H335, H400, H410 | |
| P261, P273, P305+351+338, P501 | |
| NFPA 704 | |
| Flash point | Non-flammable |
| US health exposure limits (NIOSH): | |
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PEL (Permissible)
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TWA 1 mg/m3 (as Cu) |
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REL (Recommended)
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TWA 1 mg/m3 (as Cu) |
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IDLH (Immediate danger)
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TWA 100 mg/m3 (as Cu) |
| Related compounds | |
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Other anions
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Copper(I) fluoride Copper(I) chloride Copper(I) bromide |
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Other cations
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silver(I) iodide |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| 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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