Ammonium nitrate, like some other ammonium compounds, is unstable both at high temperatures and at high pH. At high temperatures it decomposes into nitrous oxide and water, while in highly basic aqueous conditions ammonia is evolved, leaving the nitrate ion in solution.
In a very useful double replacement reaction, ammonium nitrate can be reacted with sodium hydroxide or sodium carbonate in somewhat differing procedures to yield sodium nitrate, an oxidizer that is usually preferable to ammonium nitrate, and ammonia gas, which can be channeled into cold water to produce a solution. When sodium hydroxide is used, the chemicals should be added in dry form to a round-bottom or erlenmeyer flask with a stopper and gas tubing ready to channel the ammonia. Upon the addition of a small amount of water or ice a vigorous reaction begins. If sodium carbonate, which is cheaper and safer, is used instead, the two reactants must be combined in solution and the solution heated until the reaction is complete, when ammonia can no longer be smelled.
Ammonium nitrate can decompose very violently if mixed with a fuel such as diesel or kerosene and hit by a shock wave. This mixture is a high explosive called ANFO(ammonium nitrate-fuel oil). In addition to being very dangerous, detonation of ANFO is very likely to be heard very far away and will almost certainly lead to trouble with the law, so it is not advised.
Ammonium nitrate appears typically as a hard off-white white crystalline solid or as prills, such as those found in instant cold packs. The dissolution of ammonium nitrate in water is very endothermic, making it useful for cooling baths. While it is already very soluble in cold water, ammonium nitrate is extremely soluble in boiling water, at 1024 grams/mL. These factors make re-crystallization difficult, as instead of crystals you are more likely to end up with a large brick of wet ammonium nitrate. Boiling a solution completely to dryness is very dangerous, as rapid decomposition will begin if the solid heats too much, producing nitrous oxide, a potent oxidizer. While only mildly hygroscopic, it is very difficult to dry ammonium nitrate after crystallization, and it is nearly impossible to do without the use of an oven or desiccator.
Due to the use of ammonium nitrate in explosives, the availability of this chemical varies greatly with the country it is being purchased in. It is easily obtainable in often nearly pure form in cheap instant cold packs at pharmacies in the United States. Larger amounts can sometimes be found as a fertilizer, either by itself or with calcium nitrate. In many other countries, however, it is not only sold but restricted or altogether illegal due to fear of its use in bombings.
Ammonium nitrate is a sensitive oxidizer, though not as sensitive as chlorates or perchlorates, and mixtures of it with organic compounds pose a great danger in substantial amounts. If mixed with bases, toxic and irritating ammonia gas is given off, and in high heat ammonium nitrate decomposes to form nitrous oxide, which can be a dangerous airborne oxidizer in enclosed spaces. While not a matter of physical safety, the purchase, possession, or synthesis of ammonium nitrate is often frowned upon by law enforcement, and may require a license in some jurisdictions.
Ammonium nitrate should be stored in closed containers or bags as it is mild hygroscopic, away from any reducing agents or bases.
Ammonium nitrate can be safely released in the environment, in small quantities, except water bodies.