What is Sodium Nitrate?
Sodium nitrate is an inorganic nitrate salt of an alkali metal with the chemical formula NaNO3. Commonly referred to as Chile saltpeter, this compound consists of a sodium cation (Na+) and a nitrate anion (NO3–). At room temperature, sodium nitrate exists as a white, crystalline solid which is highly soluble in water.
This compound is non-flammable. However, it is a strong oxidizing agent and can react with many flammable compounds in a violent manner. NaNO3 decomposes explosively when heated to temperatures above 538oC.
Rich deposits of sodium nitrate can be found in some South American countries such as Chile and Peru. The primary applications of this compound are in agriculture (fertilizers) and pyrotechnics.
Sodium nitrate features an ionic bond between one Na+ ion and one NO3– ion. The structure of an NaNO3 molecule is illustrated below.
The nitrate anion has a trigonal planar structure in which 3 oxygen atoms are bonded to a central nitrogen atom. The negative charge on this ion is delocalized due to resonance. Therefore, the nitrogen atom a charge of +1 whereas each oxygen atom carries a charge of -⅔. The net formal charge on the NO3– is -1.
The industrial synthesis of sodium nitrate involves the neutralization of nitric acid with sodium carbonate, sodium bicarbonate, or sodium hydroxide. The chemical equations for these reactions are listed below.
- NaHCO3 + HNO3 → NaNO3 + H2O + CO2
- Na2CO3 + 2HNO3 → 2NaNO3 + CO2 + H2O
- NaOH + HNO3 → NaNO3 + H2O
It is important to note that the reaction between sodium hydroxide and nitric acid is a highly exothermic one (since NaOH is a strong base and HNO3 is a strong acid). Therefore, an alternate method of preparing sodium nitrate is by reacting sodium hydroxide with ammonium nitrate instead of nitric acid. The chemical reaction is:
NH4NO3 + NaOH → NH4OH + NaNO3
Alternately, ammonium nitrate can be reacted with sodium carbonate or sodium bicarbonate.
Na2CO3 + 2NH4NO3 → (NH4)2CO3 + 2NaNO3
NaHCO3 + NH4NO3 → NH4HCO3 + NaNO3
Properties of NaNO3
|Molar Mass||84.99 grams per mole|
|Density||2.257 grams per cubic centimeter|
|Melting Point||308oC (581 K)|
|Boiling Point||380oC (653 K, Decomposes)|
- Sodium nitrate is a crystalline solid which is white in color.
- It has two crystal structures – rhombohedral and trigonal.
- This compound has a sweet odor.
- The solubility of NaNO3 in water corresponds to 91.2g/100mL at a temperate of 25o
- This compound is also highly soluble in ammonia.
- When dissolved in water, sodium nitrate dissociates into Na+ and NO3–
- It is a very strong oxidizing agent; it reacts violently with reducing agents.
- At high temperature, this compound is known to explosively decompose.
What are the Uses of Sodium Nitrate?
Owing to its high solubility in water, low cost, and nitrogen content, sodium nitrate is used in several fertilizers. Some other uses of this compound are listed below.
- Hybrid forms of aqua regia can be prepared with the help of NaNO3. These hybrids also have the ability to dissolve gold.
- This compound is widely used as a food additive since it acts as a preservative.
- Sodium nitrate is used as an oxidizer in several types of fireworks.
- It is also a component of some instant cold packs.
- NaNO3 is one of the components used for the storage and transfer of heat in some solar power plants.
- In order to promote the growth of Nitrosomonas bacteria, this compound is added to the wastewater in several wastewater treatment plants.
Sodium nitrate is also used in several rocket propellants and is known to be a substitute for potassium nitrate in gunpowder.
Sodium nitrate was referred to as ‘white gold’ in the 19th century. Wars have been waged over lands that were rich in sodium nitrate. The war of the Pacific, which was waged between 1879 and 1884, is commonly referred to as the saltpeter war. The South American country of Chile fought against Bolivia and Peru in order to obtain territory in the Atacama desert (which was rich in sodium nitrate).
The development of the Haber process led to a decrease in the demand for saltpeter. This is because NaNO3 could now be produced synthetically with the help of ammonia. Eventually, the mining of NaNO3 from natural deposits became obsolete.
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