By: Paul Gilmore III
Table of Contents
Paul Gilmore III
15 April 2013
Silver Iodide is an inorganic compound represented by the formula AgI that is used in cloud seeding, photography, and can also be used as an antiseptic. These are the three main ways the compound has been used throughout the history of the world. While the compound remains to be used there have been a few concerns raised that the compound silver iodide may be toxic to humans and other organism. This paper will discuss the uses of silver iodide, whether or not the compound is toxic, and the compound itself discussing silver iodides properties. II. Properties
Silver Iodide is found as a bright yellow solid. The compound is found in three different types of structures or phases. This change in structure or phase is related to the temperature the -compound is in. The B-phase or structure is the most common of the structures this structure is most stable below 147 degrees Celsius or 420 K. The B- phase is when the chemical has a wurtzite crystal structure (Figure 1)(Silver Iodide 1) and is bright yellow. In the B-phase silver iodide is commonly known as the mineral iodargyrite (Figure 2)(Silver Iodide 1). Silver iodide also is found in the a-phase when above 420 K or 147 degrees Celsius. This structure or phase has a body-centered cubic structure. In this form the silver centers are moved randomly between 2-4 coordinate sites randomly. Also in this phase the compound silver iodide is a fast conductor of ions, because of the Ag ions moving quickly throughout the compound. The structure changes between the B and s phase because of the silver sublattice melting. There is also another phase that exist under 147 degrees Celsius or 420 K called the y-phase but it is not as common as the B- phase. Throughout all the phases there are properties that are continuous. One continuous property being the molar mass of 234.77 g/mol. It appearance also seems to stay the same a bright yellow solid. The melting point of the compound is 558 degrees Celsius, 831 K 2743 degrees Fahrenheit. Silver iodides boiling point is 1506 degrees Celsius, 1779 K, 2743 degrees Fahrenheit. The compound also lacks an odor and is soluble in acid. Figure 2Figure 1 III. Cloud Seeding
Cloud Seeding is weather modification done purposely by humans to get certain results in weather. This is mostly done to control the amount of precipitation that occurs in a given area. The goal intent of cloud seeding most of the time is to increase the precipitation in a given area. However, this method of weather modification has been used to attempt to stop hail, fog, and hurricaines. The compound silver iodide happens to be the main chemical used in this form of weather modification. This is because of silver iodides crystalline structure similar to the structure of ice. Cloud seeding requires the clouds to contain supercooled liquid water, which is water in the liquid form colder than 0 degrees Celsius. This can be done by introducing silver iodide to the cloud. The silver iodide compound induces freezing through nucleation and cause the cloud to become supercooled (Sohaila and Pirhayati 85) . A problem with cloud seeding has been that many have discounted it. In 2010 the University of Israel stated that silver iodide may not be effective as we once believed. One problem with the effectiveness of cloud seeding is there is no true way to measure the effectiveness because one could not measure the amount of rain that would have been without the clouds being seeded. There have also been worries about cloud seeding’s effect on the environment and to the health of people and organism in the area. These worries have been brought up by the fact silver iodide is being used....
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