Is Ammonium Chloride Flammable?

Is Ammonium Chloride Flammable?

Ammonium chloride (NH4Cl) is not flammable. But it can produce dangerous fumes in a fire. Additionally containers containing this substance can explode under severe circumstances.

Ammonium chloride is a white solid in its pure form. Chemically it is a weak acid and can react with a series of other substances. Ammonium chloride can react violently with silver nitrate (AgNO3), potassium perchlorate (KClO4), bromine trifluoride (BF3) among others.

If ammonium chloride goes in contact with a fire or it is subjected to very high temperatures dangerous gases can be released as a result of decomposition of ammonium chloride. Possible gases released in said circumstances include nitrogen dioxide (NO2), hydrochloric acid (HCl) and ammonia (NH3).

General Properties of Ammonium Chloride

Ammonium chloride is a white crystalline solid. It has a solubility in water of around 35% (weight/volume). Ammonium chloride occurs naturally as a relatively rare mineral called salammoniac.

Below are represented some data regarding ammonium chloride.

Molecular formulaNH4Cl
Molecular weight53.5 g/mol
Density1.52 g/cm3
Boiling point520 ºC (decomposition takes place under this temperature)
Vapor pressure at 20 ºC0.01 atm
Flash Point, autoignition temperature, explosive limitsNo data

When ammonium chloride is solubilized in water the temperature of the water decreases. This means that, unlike most dissolutions, the dissolution of ammonium chloride in water absorbs heat from the vicinity.

The passage of NH4Cl + H2O to NH4+ and Cl is endothermic (that is why the temperature drops when ammonium chloride is solubilized in water). This process is an uncommon case because most endothermic processes do not occur without adding energy to the system.

One of the main means of ammonium chloride production is by the Solvay process. The salamoniac mineral is found in areas with volcanic activity near fumaroles (vents that release fumes).

Ammonium chloride is considered a weak acid when it is solubilized in water. A solution of 5% ammonium chloride has a pH of around 5 (a weakly acidic solution). Ammonium Chloride can be formed as the product of the acid-base reaction of hydrochloric acid (HCl) and ammonia (NH3) in an aqueous solution.

As it can be seen in the above chemical equation, the formation of ammonium chloride from hydrochloric acid and ammonia is a reversible reaction. This means that ammonium chloride and water can form hydrochloric acid. In this case heat favors the formation of HCl and NH3.

When heating ammonium chloride it can appear to be just evaporation, however it decomposes, forming dangerous hydrochloric acid gas and ammonia gas. Ammonia gas can be explosive at high concentrations. Besides, hydrochloric acid corrodes metals.

Ammonium Chloride Dangerous Reactions

Even Though ammonium chloride is non-flammable, non-combustible and non-explosive, ammonium chloride can react with some chemicals and produce unstable substances that pose fire hazards.

As a general rule, ammonium chloride reacts violently with strong oxidizing agents and strong basic agents.Following, the chemical reactions of ammonium chloride with silver nitrate and potassium chlorate are briefly presented.

Ammonium Nitrate Can Be Produced from Ammonium Chloride And Silver Nitrate

Ammonium nitrate (NH4NO3) can act as a strong oxidizing agent in the presence of a combustible material and heat. Ammonium nitrate can be formed from the chemical reaction of ammonium chloride and silver nitrate.

This reaction usually requires these two chemicals to be mixed in a solution of a liquid capable of solubilizing both of them. An example of such a liquid is water. If ammonium nitrate is dissolved in water it is very unlikely to promote an explosion.

Ammonium Chloride and Potassium Perchlorate Chemical Reaction

Ammonium chloride reacts violently with potassium perchlorate (KClO4) to form ammonium perchlorate (NH4ClO4) and potassium chloride (KCl). Not only is this reaction violent, the formed product ammonium perchlorate is an explosive chemical.

Ammonium perchlorate is a very strong oxidizing agent, in its presence combustible materials such as cotton based clothing can be ignited.

Ammonium Chloride Common Applications

About 90% of the produced ammonium chloride is used to produce fertilizers such as chloro ammonium phosphate (NH3ClPO4). Other applications for ammonium chloride include:

  • On the preparation of metals to be galvanized, soldered or tin-coated as a flux.
  • In the production of dry cells of electric batteries.
  • To create cooling water baths in laboratories.
  • In paleontology and archaeology, as a photographic contrasting agent.
  • In cough medicine.
  • Flavoring agent in licorice.

Hazards of Exposure to Ammonium Chloride

Overall, exposure to ammonium chloride has moderate hazards such as:

  • Skin irritation if in contact with skin.
  • Shortness of breath, cough, nausea, and headache if inhaled (at moderate temperature ammonium chloride vapor pressure greatly exceeds the American Conference of Governmental Industrial Hygienists). 

At ordinary temperature and pressure the vapor pressure of ammonium chloride corresponds to around 1300 ppm. Therefore, the most common means of exposure to this chemical is the contact with its fumes, which are finely divided particles dispersed in the air.

These fumes may cause severe eye irritation. Furthemore, under perpetual exposure an asthma-like allergy can take place. It is also possible for kidney function to be affected.

In the case of accidents in which ammonium chloride exposure has occurred, immediate medical attention must be taken. Below some first aid measures are listed:

  • Skin Contact: Immediately flush skin with water and disinfectant soap, and use an emollient on the irritated area.
  • Eye Contact: Rinse eye(s) with water for at least 15-20 minutes. Protect the unexposed eye.
  • Ingestion: Rinse mouth thoroughly with water. Do NOT induce vomiting.
  • Inhalation: Move to fresh air and administer artificial respiration if needed.

Some Precautions Measures to Avoid Ammonium Chloride Exposure Hazards

Ideally, any direct exposure would be avoided. In order to decrease the chances for exposure the following measures are recommended in the workplace:

  • Wearing proper protective clothing, eyewear and impermeable gloves.
  • Ensure that adequate ventilation and eyewash stations are properly installed in areas where ammonium chloride is being handled.
  • In case of uncertainty of clothes contamination, change into clean clothing should take place.

Additionally, the concentration of airborne particles of ammonium chloride should be monitored. 

In the event of a fire going in the workplace where ammonium chloride is being handled it must be considered toxic and explosive gases (ammonia, hydrochloric acid and nitrogen dioxide).

Conclusion

Ammonium chloride has no direct fire hazards associated with it. This chemical does have some indirect fire hazards associated with it. These fire hazards involve laborious conditions such as long exposure to heat followed by subjection to an existing fire.

More specifically, prolonged heating of ammonium chloride in a confined space could lead to an ammonia gas built up which in turn could lead to an explosion.But such a scenario is very unlikely to take place.

Ammonium chloride, as most chemicals, should never be mixed with other chemicals without the proper knowledge of the possible outcomes and safety precautions in place.

Frequently Asked Questions (FAQ):Is Ammonium Chloride Flammable?

Is Ammonium Chloride Explosive?

No, ammonium chloride is not explosive under ordinary conditions. Ammonium chloride can go through a chemical reaction with silver nitrate and produce ammonium nitrate, which is capable of generating an explosion in the presence of fuel and high heat.

What Happens When Ammonium Chloride is Heated?

At ordinary temperatures and pressure ammonium chloride is a white solid with a vapor pressure of around 0.01 atm. As it is heated the amount of ammonium chloride in the air increases proportionally to the temperature. At 338 ºC (1 atm) ammonium chloride is observed to start to chemically decompose into hydrochloric acid gas and ammonia gas. Hydrochloric acid is extremely corrosive and can violently react with basic materials. Ammonia gas is an explosive and toxic substance. At a temperature of 520 ºC, a significant portion of ammonium chloride may have decomposed but any remaining ammonium chloride will go to the gaseous phase.

Is Ammonium Chloride Hazardous?

Ammonium chloride has some hazards associated with exposure by skin contact and inhalation. Ammonium chloride has a lethal median oral dose of 1.65 g/Kg in rats, meaning ingestion at such a dose causes the death of an average of  50% of the tested rats.

Is Ammonia A Fire Hazard?

Yes, ammonia (NH3) has fire associated hazards. Tanks containing ammonia have an inherent risk of explosion if they are damaged or heated. Fires that go in contact with ammonium chloride can lead to the formation of ammonia.

What Should You Not Mix With Ammonium Chloride?

There is an extensive list of chemicals that should not be mixed with ammonium chloride. These chemicals include oxidizing agents such as sodium hypochlorite (main ingredient of bleach besides water), strongly basic chemicals such as sodium hydroxide and some silver salts (silver nitrate for example). In extremely unlikely scenarios ammonium chloride can ultimately lead to the formation of highly toxic chloramine gas (NH2Cl), if ammonia is first produced from ammonium chloride decomposition and subsequently mixed with bleach.

What Happens WHen You Mix Water and Ammonium Chloride?

The solid ammonium chloride will readily dissolve in water forming the dissociated ions of ammonium chloride NH4+ and Cl. The maximum amount of ammonium chloride that can be dissolved in one liter of water is around 35 g. Passing this amount the extra ammonium chloride will not be dissolved and remain visible in the solution. Simultaneously to the dissolution, the frask in which this mixing takes place will start to cool, that is because the dissociation of ammonium chloride in water is an endothermic process (a process that absorbs heat from the system).

What Do You Use Ammonium Chloride For?

The vast majority of ammonium chloride is used in the production of fertilizers. A smaller fraction of ammonium chloride is used in some medicinal treatments for coughs. Ammonium chloride is also used in some categories of electric batteries as well as a contrasting agent in photography.

References

Jay A. Young. Journal of Chemical Education 2005 82 (11), 1618

DOI: 10.1021/ed082p1618. https://doi.org/10.1021/ed082p1618 

Medical use:

Shelly Rainforth Collins PharmD, BCGP, in Gahart’s 2022 Intravenous Medications, 2022. Chapter 1.

Safety Data Sheets as Provided in the Merk website:

https://www.sigmaaldrich.com/US/en/sds/aldrich/254134

GLASNER, A., WEIDENFELD, L. Thermal Decomposition of Potassium Perchlorate. Nature 166, 109–110 (1950). https://doi.org/10.1038/166109a0 

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