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Ammonium dihydrogen phosphate

physical science Maturity 11-13 Next article →

Ammonium dihydrogen phosphate is a versatile chemical compound. Many people call it ADP or MAP for short. Its chemical formula is (NH4)(H2PO4). This substance is vital for modern life. It serves as a key ingredient in many agricultural fertilizers. It is also used in dry chemical fire extinguishers. Beyond these uses, it plays a role in optics and electronics. This compound helps us grow food, stay safe, and build technology.

Factories use a specific process to create monoammonium phosphate. They combine phosphoric acid with ammonia in exact proportions. This process is an exothermic reaction. This means the chemical reaction releases heat as it occurs. During this reaction, crystalline MAP begins to precipitate. Precipitation is when a solid forms out of a liquid solution. The resulting crystals often look like needles or elongated prisms.

This compound has unique physical properties. It is soluble in water. This means it can dissolve easily in water. When it crystallizes from water, it forms an anhydrous salt. This salt belongs to the tetragonal crystal system. However, it is practically insoluble in ethanol. The substance is also quite stable under heat. It can remain stable at temperatures up to 200 °C. If it reaches that temperature, it undergoes thermal decomposition. It breaks down into gaseous ammonia and molten phosphoric acid. At 125 °C, the partial pressure of the ammonia is 0.05 mm Hg.

Agriculture is the largest user of MAP by weight. It is a major component of fertilizers. It provides soil with two essential elements. These are nitrogen and phosphorus. Plants use these elements to grow. One common NPK label for this fertilizer is 12-61-0. This label tells us the specific contents of the mix. It contains 12% elemental nitrogen by weight. It also contains 61% phosphorus pentoxide. This amount is equivalent to 27% elemental phosphorus.

In the world of technology, ADP is very important. It is used in the field of optics. This is because of its birefringence properties. Birefringence means the crystal can split light into two rays. Because of its tetragonal structure, it has negative uniaxial optical symmetry. It is also used in the field of electronics. ADP crystals are piezoelectric. This means they can convert mechanical energy into electricity. This property is required for some active sonar transducers.

History shows how ADP changed electronic tools. In the 1950s, ADP crystals became widely used in transducers. They largely replaced quartz and Rochelle salt. There were two main reasons for this change. First, ADP crystals are easier to work with than quartz. Second, ADP is better than Rochelle salt for certain uses. Rochelle salt is deliquescent. This means it absorbs too much water from the air. ADP does not have this problem.

Even in nature, this compound can be found. It appears as a rare mineral called biphosphammite. This mineral forms in guano deposits. There is also a related compound called phosphammite. This is the monohydrogen counterpart. Phosphammite is even more scarce than biphosphammite. While it is a serious chemical, it is also used for fun. Because it is relatively non-toxic, it is used in toy kits. These kits allow people to grow recreational crystals. The crystals are often mixed with dyes to create different colors.

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