The Preparation of an Explosive: Nitrogen Triiodide Ammoniate
Yuri D. Blake
Department of Chemistry & Physics, Georgia College & State University,
Milledgeville, GA 31061
Conducted on: September 16, 2008
CHEM 3010L
under Dr. Julia K. Metzker
Abstract: Thislabinvolved the soaking of iodinecrystalsinconcentratedammonia, then drying of the compound to demonstratetheinstability and sensitivity of the newly produced nitrogen triiodide ammoniate compound by detonating it with the slightest of force producing a gust of purple iodine vapor and a loud snapping noise.
Introduction: Nitrogen triiodide is a highly reactive compound that when barely agitated, will explode in its unstable state; it is produced by the reaction of solid iodide crystals and concentrated ammonia, in which the iodine atoms are displaced by the hydrogen atoms as shown Fig 1.11. It is not a very practical compound do to its high instability and cost. Once the nitrogen triiodide is produced it remains stable until it is dry to form the nitrogen tri-iodide monoammine NI3·(NH3).
3I2 + NH3 -> NI3 + 3HI Fig 1.1
Spreading it out or making small piles ensures that the explosion will take place effectively. The explosion involves the release of nitrogen and iodine gases, producing a purple smoke and a snapping/popping noise. Nitrogen-nitrogen bonding is highly unstable as is nitrogen bonded to other oxidizing agents. The explosion in the experiment occurs due to nitrogen’s weak bonging, except in cases in which it is bonded to hydrogen, which makes nitrogen highly reactive. Due to these characteristics, the reaction is thermodynamically favorable to the formation of N2 1. Other nitrogen halides that have been synthesized are NF3 and NCl3, which are also volatile, but NF3 is more stable due to the low fluorine-fluorine bond energy and short bonds.
The first suggestion of the formula for nitrogen iodide was given by Bunsen in 1852, to be NH3 ∙ NI3, which supports the decomposition and reaction that takes place. In 1921, Eggert investigated this decomposition and came up with an equation to support the detonation that occurs in the reaction by the equation in Fig 1.2.3
8 NH3 ∙ NI3 à 5N2 + 6NH4I + I2 Fig. 1.2
During the reaction, the small central nitrogen atom is being crowded by the large iodine atoms leading to their unwanted non-bonded repulsive interactions as demonstrated in Fig 1.3 below:
Fig 1.3 The small central nitrogen atom is congested by the large iodine atoms, causing their unwanted repulsions.4
Experimental: One hundred three milligrams of solid iodine was placed in a 10-mL beaker equipped with a magnetic stirring bar. The beaker was set on the magnetic stirring hot plate and placed under the hood. One milliliter of concentrated ammonia was administered to the beaker and allowed to stir in suspension for five minutes. To isolate the product, the compound was spread out over several pieces of filter paper and a paper towel. The material was allowed to dry for about one hour. The reddish brown solid remaining formed the nitrogen triiodide monamine and at a distance, the solid was struck with the end of a yard stick. After the strike, the material immediately made a loud snap and a gust of purple, iodine gas was released.1
Data: Whileconductingtheexperiment,severalobservationsweremade.The iodinewasadeeppurplecrystal,whichstainseasily.Carefully added concentrated ammonia was added to the iodine, under the hood to prevent absorption or inhalation, which was a greenish color. The iodine reacted with the ammonia and was allowed to dry. While this occurred, the solution set in to a dark purplish color in its stable state and began to turn reddish brown as the ammonia evaporated off. Once the solution dried, the NI3 was immediately instable. NI3 explodes
Fig 3.
One mole of N2 is created at 944 kJ mol-1 and 3 I-I at 151 kJ mol-1 producing 1397 KJ mol-1. The change in energy is equal to the enthalphy of the reactants deducting the enthalphy of the products, giving the highly exothermic reaction (Fig. 3) and overall energy change of -437 kJ mol-1. 5
Results and Discussion: The iodine reacts with ammonia to produce the nitrogen triiodide ammoniate in its stable form. As it dries, the compound loses its stability due to the formation of the nitrogen gas, and causes an easy explosion. In the reaction, the iodine atoms are displacing the hydrogen atoms in ammonia, as shown.
Nitrogentriiodideishighlyunstablecompoundduetotheweakbondsofthenitrogentotheiodineatomsandthesizedifference(nitrogencannotholdtheiodineatoms). The compound was able to be transported and handled while in its stable form, but as it began to dry, it became much more sensitive as it became more and more unstable. Once the compound is dry and therefore unstable, the electrons of iodine atoms are forced together causing an unwanted repulsion (lone pair-lone pair repulsion), and therefore, the instability. The compound detonated upon striking and sounded off with a snap. A gust of purple iodine gas was released. A reddish orange burnt residue remained. (Fig 4)
Fig 4. Explosion conducted by Tiffany Shoham and Yuri Blake
Conclusion: This experiment was conducted successfully because the explosion did occur to prove our sample was prepared correctly. Although this compound is easily prepared, it is very dangerous and should be handled with caution. Future experiments may include repeating this laboratory and making the drying process more efficient by using larger or smaller quantities of sample or drying materials, to yield better explosion.
References:
1. Singh, M. Preparation of an Explosive: Nitrogen Triiodide Ammoniate. Microscale Inorganic Chemistry: A Comprehensive Laboratory Experience; J. Wiley: New York 1991; pp. 199-201
2. Chen, P.S. Entertaining Educational Chemical Demonstrations; Chemical Elements Publishing Co.: Camarillo, Ca 1974
3. Meldrum, F.R. "The Thermal Decomposition of Nitrogen Iodide" Bristol University The Royal Society: 1940. p410
4. Cotton, Simon. “Nitrogen Triiodide” http://www.chm.bris.ac.uk/motm/ni3/ni3j.htm
5 “Type of Explosives” <http://www.chem.shef.ac.uk/chm131- 2001/chb01ajb/types_of_explosives.html
Acknowledgements: I would like to thank my lab partner Tiffany Shoham. I would also like to thank Mehul Patel , Evan White and Leah Corley for helping me to revise my work.
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