Among the compounds of nitrogen with hydrogen, a special place belongs to ammonia. It is the most important product of chemical production and is used in many fields of human activity. In our article, we will familiarize ourselves with the molar mass of ammonia and study its basic physical and chemical properties.
Molecule structure
The substance has the formula NH 3 , hydrogen atoms are bonded to the central nitrogen particle by covalent polar bonds. Common electron pairs are strongly displaced to the nitrogen atom; therefore, the molecules are dipoles. Between them weak hydrogen bonds arise, which determine the excellent solubility of the compound in water. So, one of its volume can absorb up to 700 parts of NH 3 . The molar mass of ammonia is 17 g / mol. A solution of a substance in water is called ammonia or ammonia water. It is used in medicine in fainting conditions, since inhaling the vapor of a substance excites centers of respiration in the cerebral cortex.
Physical characteristic
Gaseous ammonia is almost twice lighter than air, has no color. When cooled to -33.4 or increased pressure, it quickly liquefies, passing into a colorless liquid phase. Gas is easily recognized, because the smell of ammonia is specific and very harsh.
The compound is readily soluble in water, forming ammonia. Upon boiling, the NH 3 molecules rapidly evaporate. Ammonia is a toxic substance, therefore, all chemical experiments with it require conducting under the hood with great care. Inhalation of gas vapors causes irritation of the mucous membrane of the organ of vision, pain in the stomach and shortness of breath.
Ammonium hydroxide
In a solution of ammonia water there are three types of particles: ammonia hydrates, anions of hydroxyl groups and ammonium cations NH 4 + . The presence of hydroxide ions gives the ammonia solution an alkaline reaction. It can be detected using indicators, for example, colorless phenolphthalein, which becomes raspberry in ammonia water. In the process of the interaction of hydroxyl anions with ammonium cations, ammonia particles are formed again, the molar mass of which is 17 g / mol, as well as water molecules. When they interact with each other, the particles are bound by hydrogen bonds. Therefore, an aqueous solution of the substance can be expressed by the formula NH 4 OH; it is called ammonium hydroxide. The compound exhibits weak alkaline properties.
Features of the NH4 + ion
A complex ammonium ion is formed using the donor-acceptor mechanism for the formation of covalent bonds. The nitrogen atom acts as a donor and provides two of its electrons, which become common. A hydrogen ion gives up a free cell, becoming an acceptor. As a result of the combination of ammonium cations and hydroxide ions, ammonia molecules appear, the smell of which is immediately felt, and water. The equilibrium of the reaction shifts to the left. In many substances, ammonium particles are similar to positive ions of monovalent metals, for example, in the salt formulas: NH 4 Cl, (NH 4 ) 2 SO 4 — ammonium chloride and sulfate.
Acid Reactions
Ammonia reacts with many inorganic acids to form the corresponding ammonium salts. For example, as a result of the interaction of perchloric acid and NH 3 we obtain ammonium chloride:
NH 3 + HCl = NH 4 Cl
This is a joining reaction. When heated, ammonium salts decompose, while gaseous ammonia is released, the boiling point of which is -33.34 ° C. They also have good solubility in water and are capable of hydrolysis. Ammonium salts decompose upon heating, and gaseous ammonia is released. They also have good solubility in water and are capable of hydrolysis. If the ammonium salt is formed by a strong acid, then its solution has an acid reaction. It is caused by an excess of hydrogen ions, which can be detected using an indicator - litmus, which changes its violet color to red.
How is molar mass measured
If a portion of a substance contains 6.02 × 10 23 structural units: molecules, atoms or ions, then we are talking about a quantity called the Avogadro number. It corresponds to the molar mass, g / mol is the unit of its measurement. For example, 17 grams of ammonia contains the number of Avogadro molecules or 1 mol of a substance, and 8.5 grams contains 0.5 mol, etc. Molar mass is a specific unit used in chemistry. It is not equivalent to physical mass. There is another unit of measure that is used in chemical calculations. This is a mass of 1 mole of ammonia equivalent. It is equal to the product of the molar mass and the equivalence factor. It is called the molar mass of the equivalent of ammonia and has a dimension of mol / L.
Chemical properties
Ammonia gas is a combustible substance. In an atmosphere of oxygen or hot air, it burns with the formation of free nitrogen and water vapor. If a catalyst is used in the reaction (platinum or trivalent chromium oxide), then the products of the process will be different. This is nitrogen monoxide and water:
NH3 + O2 → NO + H2O
This reaction is called catalytic oxidation of ammonia. It is redox, it has ammonia, the molar mass is 17 g / mol, it exhibits strong reducing properties. It is also able to react with copper oxide, reducing it to free copper, gaseous nitrogen and water. The gas can react with concentrated hydrochloric acid even in the absence of water. Known experience, which is called: smoke without fire. One glass rod is immersed in ammonia, and the other in concentrated chloride acid, then they are brought together. The appearance of white smoke is observed, which is formed by the resulting small crystals of ammonium chloride. The same effect can be achieved by placing tubes with two solutions side by side. The equation of ammonia with perchloric acid was given by us above.
With strong heating, the molecules of the substance decompose into free nitrogen and hydrogen:
2NH3 ⇄ N2 + 3H2
How to recognize an NH4 + ion
Ammonium salts react not only with acids, but also with alkalis. As a result, gaseous ammonia is released, which is easily determined by the olfactory organ. This proves that this salt contains ammonium ion.
A more accurate indicator that the interaction of alkali and ammonium sulfate releases the NH 4 + cation is a moist universal litmus paper. She changes color from red to blue.
Industrial synthesis of ammonia
A gaseous compound is produced by direct reaction of a hydrogen compound obtained by conversion from water and nitrogen extracted from air. The process is catalytic (using metallic iron containing impurities of potassium and aluminum oxides). At the same time, the fact that the boiling point of ammonia is -33.4 ° C is taken into account. The exothermic reaction of the synthesis of ammonia requires an increase in pressure in the reacting gas mixture to 450 - 460 ° C. To increase the practical yield of the product in a reversible ammonia synthesis reaction, the purity of the reagents is controlled, and the temperature in the synthesis column is not allowed to increase.
Where is ammonia and its salts used?
Physical and chemical characteristics of a substance determine its use in various fields of industry. Its greatest amount is used for the synthesis of nitric acid, nitrogen-containing ammonium salts, soda according to the ammonia method, urea. In refrigeration plants, the substance is used, due to its ability to evaporate, while absorbing excess heat. Ammonia water and liquid ammonia are used as nitrogen fertilizer.