por We explain what ammonium sulfate is, its chemical structure, physical and chemical properties, and uses
What is ammonium sulfate?
He ammonium sulphate It is an inorganic ternary and ammoniacal salt of sulfuric acid. Its chemical formula is (NH4)2SO4. Therefore, the stoichiometric ratios say that for every sulfate anion there are two ammonium cations interacting with it. This allows the neutrality of salt ((+1)∙2 + (-2)).
Its nomenclature is due to the fact that it is a salt derived from H2SO4, changing the suffix “uric” to “ate”. Thus, the two initial protons are replaced by NH4+, product of the reaction with ammonia (NH3). So, the chemical equation for its synthesis is: 2 NH3 + H2SO4 => (NH4)2SO4
Ammonium sulfate is also prepared by the reaction of ammonium carbonate with calcium sulfate: (NH4)2CO3 + CaSO4 => (NH4)2SO4 + CaCO3, precipitating lime carbonate, which is separated from the remaining liquid.
Ammonium sulfate is a storer of nitrogen and sulfur, both essential in the chemistry of soils and fertilizers.
Chemical structure of ammonium sulfate
The top image illustrates the molecular geometries of the NH4+ and SO42- ions. The red spheres correspond to the oxygen atoms, the white to the hydrogen atoms, the blue to the nitrogen atom and the yellow to the sulfur atom.
Both ions can be considered as two tetrahedrons, thus having three units that interact to form an orthorhombic crystalline arrangement. The sulfate anion is SO42- and is capable of donating or accepting four hydrogen bonds, just like the NH4+ cation.
Ammonium Sulfate Properties
Molecular weight
132.134 g/mol.
Physical appearance
White solid. White or brown orthorhombic crystals, depending on impurity levels.
Smell
Lavatory.
Melting point
280ºC This low melting point compared to other ionic compounds is due to the fact that it is a salt with monovalent cations (+1) and with dissimilar size ions, causing the solid to have low crystal lattice energy.
Solubility
76.4 g/100 g of water at 25ºC. This affinity for water is due to the great capacity of its molecules to solvate ammonium ions. On the other hand, it is insoluble in acetone and in alcohol; that is, in less polar solvents than water.
Density
1.77 g/cm3 at 25ºC.
Vapor pressure
1,871 kPa at 20ºC.
Flash point
26ºC.
pH
5.0 – 6.0 (25 ºC. 1 M solution). The slightly acidic pH is due to the hydrolysis of NH4+ in water, producing H3O+ at low concentrations.
Stability
Stable under suitable environmental conditions. In contact with strong oxidants it can catch fire.
Decomposition
It begins to decompose at 150ºC, releasing toxic vapors of sulfur oxide, nitrogen oxide and ammonium.
Corrosion
It does not attack iron or aluminum.
Ammonium Sulfate Uses
In the agriculture
Ammonium sulfate is used as a fertilizer on alkaline soils. The ammonium salt has in its composition 21% nitrogen and 24% sulfur. However, there are compounds that provide a greater amount of nitrogen than ammonium sulfate; the advantage of the latter is its high sulfur concentration.
Sulfur is essential in protein synthesis, since several amino acids—such as cystine, methionine, and cysteine—have sulfur. For these reasons, ammonium sulfate continues to be one of the most important fertilizers.
It is used on crops of wheat, corn, rice, cotton, potato, hemp, and fruit trees.
It lowers the pH of alkaline soils due to its contribution to the nitrification process carried out by microbes. Ammonium (NH4+) is used to produce nitrate (NO3–) and release H+: 2NH4+ + 4O2 => 2NO3– + 2H2O + 4H+. The increase in the concentration of hydrogen lowers the pH of alkaline soils and allows more use.
In addition to its use as a fertilizer, ammonium sulfate acts as an adjuvant to soluble insecticides, herbicides, and fungicides, which are sprayed on crops.
Sulfate is capable of sequestering ions present in the soil and in irrigation water that are necessary for the life of certain pathogens. Among the ions that ammonium sulfate captures are Ca2+, Mg2+, Fe2+ and Fe3+. This action enhances the microbicidal effect of the mentioned agents.
As analytical reagent
Ammonium sulfate acts as a precipitating agent in electrochemical analysis, in microbiological culture medium and in the preparation of ammonium salts.
In the precipitation and isolation of proteins
Ammonium sulfate is used in the isolation and purification of proteins, especially plasma proteins. A quantity of ammonium sulfate is added to the plasma until it reaches a certain concentration; thus, the precipitation of a group of proteins is caused.
The precipitate is collected by centrifugation and an additional amount of ammonium sulfate is added to the supernatant and, at a new concentration, another group of proteins is precipitated.
The repetition of the previous process in a sequential way allows the obtaining of different fractions of plasmatic proteins as a result.
Before the new technologies of molecular biology appeared, this procedure allowed the isolation of plasmatic proteins of great importance in medicine, for example: immunoglobulins, coagulation factors, etc.
In the industry
Ammonium sulfate acts by retarding the start of fire in the textile industry. It is used as an additive in the electroplating industry. Likewise, it is used in the production of hydrogen peroxide, ammonium chloride, etc.
Other uses
Ammonium sulfate is used as an osmotic pressure regulating agent and as a salt precipitating agent.
In the form of ammonium lauryl sulfate, it lowers the surface tension of water, thus allowing the separation of contaminants by increasing the hardness of the water.
It is an anticorrosive agent.
It is used as a food additive that regulates acidity in flour dough and bread.