A ammonia, with the formula NH3, is a colorless, toxic gas with a strong and unpleasant odor. It has a pyramidal geometry, in addition to being the most soluble gas in water that is known, precisely by the formation of hydrogen bonds. It is an important substance in the global nitrogen cycle.
It is widely used as a fertilizer, since the nitrogen It is a macronutrient for plants. Its main production process is the Haber-Bosch process, developed at the beginning of the 20th century. It is a substance that inspires care, as it has great toxic potential, and in certain cases, exposure to it can be fatal.
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summary about ammonia
- Ammonia is a molecule with the formula NH3, polar, soluble in water and of pyramidal geometry.
- It is a colorless, toxic gas with a strong, unpleasant odor.
- A good part of the ammonia produced is destined for the production of fertilizers, since nitrogen is a macronutrient for plants.
- The main way to obtain ammonia synthetically is through the Haber-Bosch process, developed at the beginning of the 20th century.
- Ammonia inspires caution, and exposure to this gas can cause serious problems, including death.
- Despite being known since ancient times, it was only isolated and characterized in the 18th century.
ammonia properties
- molecular formula: NH3.
- Molar mass: 17.031 g.mol-1.
- Fusion point: -77.73 °C.
- Boiling point: -33.33 °C.
- Density: 0.696g. L-1.
- Physical appearance: colorless gas.
- Solubility: very soluble in water (≈ 530 g. L-1 at 20 °C); soluble in ethanol It is ethyl ether.
- dipole moment: 1.47 D (polar molecule).
- molecular geometry: pyramidal.
What are the characteristics of ammonia?
Ammonia is a Colorless, toxic, pungent-smelling gas. It occurs in nature, mainly through the anaerobic decay of plant and animal matter, and is also detected in outer space. Some vegetables, combined with bacteria Rhizobium, are able to fix atmospheric nitrogen and thus produce NH3, at an important stage in the global nitrogen cycle.
When you react with oxygen, in a combustion, produces nitrogen gas and water:
4 NH3 +302 → 2N2 + 6H2O
Between the gases, ammonia has the highest solubility in water, a direct consequence of the formation of its hydrogen bond with H molecules2O. It also has a slightly basic character, due to the following ionization reaction:
NH3 (aq) + H2O(l) ⇌ NH4+ (aq) + OH- (here) KB = 1.8 x 10-5
The low value of KB shows that little ammonia ionizes, so even in dilute solutions the smell of ammonia is still noticeable.
What is ammonia for?
More of 80% of the world's ammonia production is used directly or not in agriculture. Among the fertilizers that are produced using ammonia are urea, ammonium phosphate, ammonium nitrate, and other nitrates. According to the United States Geological Survey, in 2018 the world production of ammonia was about 144 million tons, with the Asia the main producer, largely due to the China.
that all whyNitrogen is one of the macronutrients of plants. and, therefore, it is an essential element for its good growth.
ammonia too important in the synthesis of nitric acid, one of the most produced and traded chemical substances in the world. The process starts with the oxidation from NH3 to NO, through the combustion of ammonia at a temperature of 1200 K in the presence of a rhodium and platinum catalyst (Rh/Pt):
4 NH3 +502 → 4 NO + 6 H2O
The NO is then mixed with air and absorbed in a countercurrent of water, producing, after a few steps, nitric acid, with a concentration of about 60% by mass.
Among minor uses is the application of ammonia in the cosmetics industry and also in the composition of cleaning products and bleaches.
Read too: Ammonium nitrate — highly reactive compound used in fertilizers and explosives
Obtaining ammonia
The main form of ammonia production is by Haber-Bosch process, first developed in 1908 by the German chemist Fritz Haber and then adapted to industrial scale by the German chemist and engineer Carl Bosch between 1909 and 1913. Both were awarded the Nobel Prize of Chemistry for the feat.
![Swedish stamp from 1978 honoring scientist Fritz Haber. [1]](/f/4b0723ee95dab53774bdd0290996b108.jpg)
A The process reaction is as follows:
No2 + 3H2 ⇌ 2 NH3
Hydrogen is produced through the methane, CH4, with steam and air, producing CO and hydrogen gas. CO itself can also react with steam to produce more hydrogen gas.
CH4 + H2O → CO + 3 H2
CO + H2O → CO2 + H2
The challenge with the Haber-Bosch process is yield, and for a good yield to be achieved, the conditions thermodynamics must be very well adjusted, in a classic application of the principles of Physical Chemistry in systems in balance.
Being an exothermic reaction (ΔH = - 92 kJ.mol-1), the increase in temperature, despite increasing the speed of chemical reaction, decreases the yield of the reaction. At a given temperature, both the rate of the reaction and its yield are increased in a situation of high pressure. The presence of a catalyst also facilitates the process. Therefore, the ideal production conditions are with the temperature close to 450 °C, a pressure of 20,260 kPa and a heterogeneous Fe catalyst3O4 mixed with K2O, SiO2 and Al2O3.
Precautions with ammonia
Ammonia is a toxic gas, yet natural concentrations of this compound are not dangerous to us. Already for those who work with this substance, attention must be constant, since at higher levels of exposure NH3 can cause serious damage, such as irritation to the skin, us eyes, in the throat and lungs, in addition to the occurrence of coughs and burns. When the ammonia concentration is in the range of 2500 to 4000 ppm (mg. L-1) in the air, it causes the death of a human being in about 30 minutes and at higher concentration levels, such as 5000 to 10000 ppm, death is practically instantaneous.
Despite all this, ammonia not classified as a carcinogen by the International Agency for Research on Cancer (IARC).
history of ammonia
Although it is understood that ammonia has been known since ancient times, one of the first references to a solution water of this substance comes from the work of Raymond Lully, a Catalan missionary who lived between the thirteenth and XIV. The book The Skeptical Chemist (from English The Skeptical Chymist), from 1661 and authored by Robert Boyle, also mentions an aqueous solution of ammonia, in the same way that Johann Kunkel van Lowenstern mentions the gas in his works.
A discovery is credited to the Englishman Joseph Pristly*, who isolated and characterized the compound in 1773 by heating an aqueous solution of ammonia (which he called the “volatile spirit of ammonium salt”). At the time, Pristly referred to the gas as "alkaline air". In 1782, the Swedish chemist Torburn Olof Bergman suggested the name ammonia for “alkaline air” and, in 1785, the French chemist Claude Louis Berthollet determined the chemical composition of ammonia.
* The American Chemical Society also credits Swede Joseph Black, Irishman Peter Woulfe, and Swede Carl Wilhelm Scheele as scientists who isolated ammonia.
By Stefano Araujo Novais
Chemistry teacher
