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Ammonium chloride

physical science Maturity 5-7 Next article →

Ammonium chloride is an inorganic chemical compound with the formula NH4Cl. It is also known as an ammonium salt of hydrogen chloride. This substance appears as a white crystalline salt that dissolves very easily in water. When this salt is mixed with water, the resulting solution is mildly acidic. In its natural mineral form, it is called salammoniac.

Ammoniumchloride crystal 01
Ammoniumchloride crystal 01

This compound is important in many different fields, from large-scale farming to specialized scientific photography.

Chemically, ammonium chloride is created through specific reactions. One common method involves combining ammonia (NH3) with either hydrogen chloride gas or a hydrochloric acid solution. In a laboratory setting, this can be demonstrated by adding these two liquids to gas-washing bottles. As air is injected into the tubes, the ammonia and hydrogen chloride gases collide and react to form a solid product. Another major production method is the Solvay process. This industrial process is used to manufacture sodium carbonate (Na2CO3). It also serves a secondary purpose by minimizing the release of ammonia during industrial operations.

Ammonium chloride also shows interesting behaviors when heat is applied. When heated, the substance appears to sublime, which means it turns directly from a solid into a gas. However, it actually undergoes a reversible decomposition. This means the NH4Cl breaks down into ammonia and hydrogen chloride gases, which can then reform into the solid salt upon cooling.

Ammonium chloride pyrolyses and reforms
Ammonium chloride pyrolyses and reforms

The compound can also react with strong bases like sodium hydroxide to release ammonia gas. It similarly reacts with alkali-metal carbonates at high temperatures to produce ammonia, alkali-metal chloride, and carbon dioxide.

Historically, humans have been interacting with this salt for thousands of years. The Romans extracted the substance from deposits near the Temple of Ammon in Siwa. Because of this location, they named it *sal ammoniacus*, or Ammonian Salt, to honor the Siwan Berber god, Ammon. The name is derived from the ancient Greek word *ammoniakos*. The ancient writer Pliny also recorded a similar salt called *hammoniacum* in the Roman province of Cyrenaica. This name was used because the salt was found near the Temple of Jupiter Amun.

Agriculture is the most significant use for this chemical today. Approximately 90% of the world's production of ammonium chloride is used as a nitrogen source in fertilizers. The compound is roughly 26% nitrogen by weight. It is frequently used to fertilize crops like rice and wheat, particularly in Asia. Farmers must apply it at specific concentrations, usually between 50 and 100 milligrams of nitrogen per liter of water. This is equivalent to about 0.2 to 0.4 grams of ammonium chloride per liter. If used incorrectly, it can acidify the soil or cause chloride toxicity in sensitive plants like beans, grapes, or avocados.

Beyond the farm, ammonium chloride serves many specialized roles. In the ocean, giant squid use a solution of ammonium chloride throughout their bodies to maintain neutral buoyancy. This works because the solution is less dense than the surrounding seawater. In medicine, it acts as an expectorant in cough medicines by irritating the bronchial mucosa to produce fluid that is easier to cough up. It is also used as a systemic acidifying agent to treat certain medical conditions like metabolic alkalosis. In the food industry, it is known as sal ammoniac or E510. It is used to make cookies crisp and provides the distinct flavor for salty liquorice in many regions.

Finally, the compound has unique properties for science and art. In the 19th century, it was essential for albumen silver prints. Photographers mixed egg whites with ammonium chloride to coat paper, creating a smooth surface for light-sensitive silver chloride. This process helped produce fine details and warm tones in early photographs. In paleontology, scientists deposit ammonium chloride vapor onto fossils. This creates a brilliant white, inert layer of tiny crystals. This layer enhances the contrast of the fossil, making it easier to photograph three-dimensional specimens in high detail.

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08. Директна синтеза на амониум хлорид.webm
File:Ammonium chloride pyrolyses and reforms.jpg
Ammonium chloride pyrolyses and reforms.jpg
File:Ammoniumchloride crystal 01.jpg
Ammoniumchloride crystal 01.jpg
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