Sodium nitrate

Sodium nitrate (also known as Chilean saltpeter) is a sodium salt with the chemical formula NaNO₃.

Properties

Chemical

Sodium nitrate decomposes in the presence of a metal to yield sodium nitrite

2NaNO₃ → 2NaNO₂ + O₂

Reaction with sulfuric acid produces nitric acid

2NaNO₃ + H₂SO₄ → 2HNO₃ + Na₂SO₄

Potassium nitrate, typically more desired as an oxidizer than sodium nitrate, can be produced in a somewhat impure form by cooling a hot saturated solution containing the proper molar amounts of both sodium nitrate and potassium sulfate. Because sodium sulfate is much less soluble than potassium nitrate, most of it will crystallize out of solution fairly quickly.

Physical

Sodium nitrate is a white solid which is very soluble in water. Unlike its potassium counterpart, sodium nitrate is hygroscopic. It's soluble in methanol, ethanol, ammonia, and hydrazine, but not in acetone.

Availability

Sodium nitrate is sold as a meat curing salt and food additive, sometimes in pharmacies. It can also be bought in larger quantities as fertilizers, which are often impure. Sodium nitrate is cheaper to produce than buy in places with easy access to ammonium nitrate.

Preparation

Sodium nitrate is prepared industrially by neutralizing nitric acid with sodium carbonate or sodium bicarbonate.

2 HNO₃ + Na₂CO₃ → 2 NaNO₃ + H₂O + CO₂

HNO₃ + NaHCO₃ → NaNO₃ + H₂O + CO₂

An easier route involves mixing a solution of sodium hydroxide and ammonium nitrate, which can be made even easier with the use of sodium bicarbonate or carbonate:

NH₄NO₃ + NaOH → NaNO₃ + NH₄OH

NH₄NO₃ + NaHCO₃ → NaNO₃ + NH₃ + H₂O + CO₂(Requires heating in solution to complete)

2 NH₄NO₃ + Na₂CO₃ → 2 NaNO₃ + 2 NH₃ + H₂O + CO₂(Requires heating in solution to complete)

Since ammonium hydroxide will quickly decompose in the basic conditions to release ammonia, the solution will contain fairly pure sodium nitrate, though heating may be required to finish decomposing it:

NH₄OH → NH₃ + H₂O

This reaction should be performed outside or in a fume hood. The reaction is self-sustaining and proceeds very quickly with wet sodium hydroxide and more slowly in dry conditions, but with the carbonate or bicarbonate is easily controlled and requires a long period of boiling of the solution.

Projects

• Making sodium nitrite
• Poor man's aqua regia
• Smoke bombs

Handling

Safety

Sodium nitrate is not very toxic, and as long as it is not consumed it's safe to handle. Medical studies indicate that long-term consumption increases the risk of several illnesses, such as stomach cancer, diabetes mellitus and Alzheimer.

Because it's hygroscopic, sodium nitrate is a poor oxidizer unless kept completely dry, through much effort, until it is used.

Storage

Sodium nitrate should be stored in closed containers, due to its hygroscopicity.

Disposal

Sodium nitrate doesn't require special disposal, although its best to avoid releasing it in the environment due to its sodium content.