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Arginine

Explosion of NI3

Introduction

This experiment demonstrates the awesome power of decomposition reactions. However, as the following warning notes, this awesome power can be dangerous, and if this experiment is carried out, it must be done with care.

The experiment consists of two parts. The first makes the nitrogen triiodide (or, as some chemists would say, nitrogen triodide).  The second decomposes it in a flash.

WARNING AND DISCLAIMER

This experiment, if done at all incorrectly, can pose a RISK OF PROPERTY DAMAGE OR INJURY. Do not attempt to carry this out if you are at all unsure of the exact procedure to follow, or if you lack any of the required supplies or equipment. 

The International Order of Nitrogen, its officers, and/or its members are not responsible for your actions.  Carry this out at your own risk.

One of the reactants (solid iodine) used in this experiment may be regulated by the U.S. Drug Enforcement Administration.  Do not do anything outside the bounds of the law.

Update (16 Jan 2003): We were advised that outdoor supply stores such as REI sell iodine tablets for drinking water purification.

Read the entire procedure TWICE before starting the experiment!

Reactions In Summary

3I2 (s) + 5NH3 (aq) --> 3NH4I (aq) + NH3*NI3 (s)

2NH3*NI3 (s) --> 5N2 (g) + 6NH4I (s) + 9I2 (g)

Facilities

To do this experiment safely, you will need to have ready access to the following:

  • Fume hood
  • Water supply
  • Eye wash station
  • Emergency shower

Supplies and Equipment

The following are listed in the order they will be used.

  • 0.5 g solid iodine (see note above reaction summary)
  • 2.0 mL 15M ammonia or ammonium hydroxide (we were told that even household ammonia, in the right amount, will work; do stoichiometry)
  • Safety glasses
  • One small mortar and pestle
  • One chemical spatula
  • One 100 mL laboratory beaker
  • One glass stirring rod
  • Two pieces of thick filter paper
  • Ringstand with attached ring slightly smaller than the filter paper
  • 50 mL ethanol
  • Safety shield
  • Paper
  • Marker
  • Meter stick or other long rod
  • Transparent, masking, or duct tape
  • Feather or wax paper
  • Earplugs

Procedure

Before going any further, be sure to have read the warning and disclaimer.

Almost every reactant and product in the experiment is corrosive and highly damaging to living tissue.  Treat accordingly.

Clean up any spills immediately.  Remove any clothing that touches and chemicals.  Flush any contacted skin with water for several minutes.  Use an eye wash station if eyes are affected.  If chemicals contact a large area of the body, use an emergency shower.  If any non-skin area of the body or a large region of the skin is contacted, seek medical attention immediately.

  1. Put on safety glasses.
  2. Do steps 2 to 5 in a fume hood.
  3. If the iodine is in pellet/crystal form, add the iodine to the mortar.  Carefully crush with the pestle.
  4. Using the chemical spatula, add the iodine to the beaker.
  5. Pour the ammonia or ammonium hydroxide into the beaker.
  6. Let react for five minutes, stirring with the stirring rod occasionally.
  7. While the reaction occurs, set up the ringstand on a lab bench in a corner, with the filter paper stacked, resting on the ring.
  8. Decant the liquid into the sink (or designated disposal receptacle) and flush down with water.
  9. Using the spatula, transfer the solid to the filter paper.
  10. If any solid remains in the beaker, add the ethanol and let sit overnight in the fume hood before flushing down the sink.
  11. Carefully wash the spatula and stirring rod with water.
  12. Place the safety shield in front of the ring stand.
  13. Write "Danger!  Contact Explosive!  Do NOT Touch!  Contact (your name) for information." on the paper with the marker.
  14. Attach the paper with tape to the shield.
  15. Wait 45 minutes or until the solid on the filter paper has dried.
  16. While waiting, tape the feather or some folded wax paper to the end of the meter stick or rod.
  17. Insert earplugs and make sure that the area is clear for a three meter radius (observers should also wear earplugs)..
  18. Staying as far away from the ringstand as possible, roll the feather or wax paper in the solid on the filter paper.
  19. Observe results.
  20. If nothing happens, wait another 15 minutes and repeat steps 15 to 18.
  21. If nothing happens again, clear the area and drip water on the solid.
  22. Once saturated with water, dump the contents in the beaker containing ethanol and stir so that no solid remains in contact with air.
  23. Complete step 10.

What's Happening

When the aqueous ammonia is added to the iodine, a redox reaction occurs, resulting in solid nitrogen triiodide in complex with ammonia, surrounded by aqueous ammonium iodide. After decanting, some water remains and keeps the nitrogen triiodide relatively stable.   However, when the moisture evaporates, the nitrogen triiodide becomes unstable, partially due to the large radius of iodine. The kinetic energy of the feather or wax paper serves as the activation energy for a rapid and violent decomposition reaction, completely obliterating the nitrogen triiodide (and probably the filter paper) as the atoms reform into diatomic gases, with ammonium iodide residue.

Questions

If you fully understand what's happening in this reaction, see if you can answer the following questions for yourself:

  1. Why is it important that the iodine be solid and not in solution?
  2. Why do both ammonia and ammonium hydroxide work as reactants?
  3. If 1 g I2 is reacted at 100% efficiency with excess NH3 (aq), and the resulting NI3 is decomposed at 100% efficiency, in a 1.0 L steel vessel (so no volume change), initially at thermodynamic equilibrium with the surroundings (298 K, 1.0 atm pressure), and the temperature of the vessel is held constant during the reaction, what will the final pressure in the vessel be? Assume "ideal" conditions. You will need some knowledge of the gas laws. Hint: the pressure increase will be due to the introduction of additional moles of gas into the vessel. Also, you may neglect the volume of the initial solid.
  4. How do the pH values of the reactants and products compare?
  5. What is the driving force behind the decomposition (why is nitrogen triiodide so unstable)?
  6. Would you expect something similar to occur with nitrogen tribromide (if you could make it)?  Why?

Author: C. Shultz

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