Silver iodide

Silver iodide
Names
Other names
Silver(I) iodide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.125
EC Number 232-038-0
UNII
Properties
AgI
Molar mass 234.77 g/mol
Appearance yellow, crystalline solid
Odor odorless
Density 5.675 g/cm3, solid
Melting point 558 °C (1,036 °F; 831 K)
Boiling point 1,506 °C (2,743 °F; 1,779 K)
3×10−7g/100mL (20 °C)
8.52 × 10 −17
Solubility soluble in acid
−80.0·10−6 cm3/mol
Structure
hexagonal (β-phase, < 147 °C)
cubic (α-phase, > 147 °C)
Thermochemistry
115 J·mol−1·K−1[1]
−62 kJ·mol−1[1]
Hazards
Safety data sheet Sigma-Aldrich
not listed
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform 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
0
2
0
Flash point Non-flammable
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

Silver iodide is an inorganic compound with the formula AgI. The compound is a bright yellow solid, but samples almost always contain impurities of metallic silver that give a gray coloration. The silver contamination arises because AgI is highly photosensitive. This property is exploited in silver-based photography. Silver iodide is also used as an antiseptic and in cloud seeding.

Structure

The structure adopted by silver iodide is temperature dependent:[2]

The golden-yellow crystals on this mineral sample are iodargyrite, a naturally occurring form of β-AgI.

Preparation and properties

Silver iodide is prepared by reaction of an iodide solution (e.g., potassium iodide) with a solution of silver ions (e.g., silver nitrate). A yellowish solid quickly precipitates. The solid is a mixture of the two principal phases. Dissolution of the AgI in hydroiodic acid, followed by dilution with water precipitates β-AgI. Alternatively, dissolution of AgI in a solution of concentrated silver nitrate followed by dilution affords α-AgI.[4] If the preparation is not conducted in the absence of sunlight, the solid darkens rapidly, the light causing the reduction of ionic silver to metallic. The photosensitivity varies with sample purity.

Cloud seeding

Cessna 210 equipped with a silver iodide generator for cloud seeding

The crystalline structure of β-AgI is similar to that of ice, allowing it to induce freezing by the process known as heterogeneous nucleation. Approximately 50,000 kg are used for cloud seeding annually, each seeding experiment consuming 10–50 grams.[5]

Safety

Extreme exposure can lead to argyria, characterized by localized discoloration of body tissue.[6]

References

  1. 1 2 Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A23. ISBN 0-618-94690-X.
  2. ↑ Binner, J. G. P.; Dimitrakis, G.; Price, D. M.; Reading, M.; Vaidhyanathan, B. (2006). "Hysteresis in the β–α Phase Transition in Silver Iodide" (PDF). Journal of Thermal Analysis and Calorimetry. 84 (2): 409–412. doi:10.1007/s10973-005-7154-1.
  3. ↑ Hull, Stephen (2007). "Superionics: crystal structures and conduction processes". Rep. Prog. Phys. 67: 1233–1314. doi:10.1088/0034-4885/67/7/R05.
  4. ↑ O. Glemser, H. Saur "Silver Iodide" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1036-7.
  5. ↑ Phyllis A. Lyday "Iodine and Iodine Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. doi:10.1002/14356007.a14_381
  6. ↑ "Silver Iodide". TOXNET: Toxicogy Data Network. U.S. National Library of Medicine. Retrieved 9 March 2016.
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