Potassium nitrite

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Potassium nitrite
Names
IUPAC name
Potassium nitrite
Preferred IUPAC name
Potassium nitrite
Other names
E249
Nitrous acid, potassium salt
Properties
KNO2
Molar mass 85.10379 g/mol
Appearance Deliquescent white or slight yellow solid
Odor Odorless
Density 1.914986 g/cm3
Melting point 440.02 °C (824.04 °F; 713.17 K)
Boiling point 537 °C (999 °F; 810 K) (decomposes)
281 g/100 ml (0 °C)
312 g/100 ml (25 °C)
413 g/100 ml (100 °C)
Solubility Very soluble in liq. ammonia
Slightly soluble in alcohol
Vapor pressure ~0 mmHg
Thermochemistry
-369.8 kJ/mol
Hazards
Safety data sheet Sigma-Aldrich
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
200 mg/kg (rat, oral)
108 mg/kg (rabbit, oral)
Related compounds
Related compounds
Sodium nitrite
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Potassium nitrite is the inorganic compound with the chemical formula KNO2.

Properties

Chemical

Potassium nitrite reacts at an extremely slow rate with a liquid ammonia solution of potassium amide at room temperatures, and in the presence of ferric oxide or cobaltic oxide, to form nitrogen and potassium hydroxide.

Heating potassium nitrite above 538 °C will cause it to decompose violently and even explode.

Physical

Potassium nitrite is a white or slightly yellowish hygroscopic solid, very soluble in water. It is insoluble in most organic solvents, although it shows some solubility in low-chain alcohols which increases with temperature.

Availability

Potassium nitrite is sold by chemical suppliers. Can also be bought online.

Preparation

A quick and clean route to potassium nitrite is by bubbling an excess of nitric oxide through a solution of potassium hydroxide, with the NO being obtained by dissolving copper metal in nitric acid. Make sure to purge the air inside the installation first with nitrogen, to prevent the oxidation of nitric oxide to nitrogen dioxide, which will contaminate your final product with potassium nitrate.

Very pure potassium nitrite can be obtained by reacting nitrous acid (which can be obtained by adding dinitrogen trioxide to pure water) with a solution of potassium hydroxide.

2 KOH + N2O3 → 2 KNO2 + H2O

A simpler route involves melting potassium nitrate above 400 °C, which produces potassium nitrite and oxygen, although this route requires temperature control and the resulting hot KNO2 is susceptible to reverting back to KNO3 in the presence of oxygen/air. This method is the industrial route to potassium nitrite.

The thermal reduction of potassium nitrate with calcium sulfite will also yield potassium nitrite.

KNO3 + CaSO3 → KNO2 + CaSO4

A very simple route involves heating a mixture of potassium nitrate using starch and potassium hydroxide. This method has been tested by many hobby chemists and potassium nitrite has been identified as a product in the reaction mixture. However, the yield of this route is poor and purifying the potassium nitrite from the reaction mixture has been shown to be difficult.

Projects

  • Make alkyl nitrites
  • Make nitrous oxide
  • Destroy azides
  • Make azo compounds
  • Electrochemical grinding
  • Meat curing
  • Make nitromethane

Handling

Safety

Potassium nitrite is a strong oxidizer and may accelerate the combustion of other materials, although its hygroscopicity limits this. Like other nitrite salts, potassium nitrite is toxic if swallowed, and laboratory tests suggest that it may be mutagenic or teratogenic, due to the production of nitrosamines. Gloves and safety glasses are recommended when handling potassium nitrite.

Storage

In closed bottles, in a dry place, away from any acids.

Disposal

Potassium nitrite can be oxidized to the less harmful potassium nitrate by heating it in air until it melts but kept below 500 °C, then allowed to oxidize to potassium nitrate. A quicker route involves using an oxidizing agent, like hydrogen peroxide, either as solution or as percarbonate, which also oxidizes it to nitrate. The resulting KNO3 can then be used as fertilizer, provided it's not contaminated with nitrite or heavy metals.

Mixing it with a flammable material (like powdered sugar) and igniting it is another simple route, albeit more dangerous and somewhat less reliable due to KNO2 hygroscopicity and the possibility of various organic side products being produced.

References

Relevant Sciencemadness threads