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Ammonium Sulfate Formula Properties and Uses

What is ammonium sulfate?

Ammonium sulfate is ternary and ammoniacal inorganic salt of sulfuric acid. Its chemical formula is (NH 4 ) 2 SO 4 . Therefore, the stoichiometric proportions say that for each sulfate anion there are two ammonium cations interacting with it. This allows for the neutrality of the salt ((+1) ∙ 2 + (-2)).

Its nomenclature is due to the fact that it is a salt derived from H 2 SO 4, changing the suffix “uric” for “to”. Thus, the two initial protons are replaced by NH +, a product of the reaction with ammonia (NH 3 ). Then, the chemical equation for its synthesis is: 2 NH 3  + H 2 SO 4 => (NH 4 ) 2 SO 4

Ammonium sulfate is also prepared by reacting ammonium carbonate with calcium sulfate: (NH 4 ) 2 CO 3  + CaSO 4 => (NH 4 ) 2 SO 4  + CaCO 3, precipitating calcium carbonate, which is separated from the remaining liquid.

Ammonium sulfate is a nitrogen and sulfur buffer, both essential in soil and fertilizer chemistry.

Chemical structure of ammonium sulfate

Chemical structure of ammonium sulfate

The upper image illustrates the molecular geometries of NH + and SO 2- 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 tetrahedra, thus having three units that interact to form an orthorhombic crystal arrangement. The sulfate anion is SO 2-  and is capable of donating or accepting four hydrogen bonds, just like the NH + cation.

Properties of ammonium sulfate

Molecular weight

132.134 g / mol.

Physical appearance

Solid white. White or brown orthorhombic crystals, depending on impurity levels.

Odor

Lavatory.

Melting point

280 ° C. This melting point, low compared to other ionic compounds, is due to the fact that it is a salt with monovalent cations (+1) and with dissimilar ions in their sizes, causing the solid to have low crystalline lattice energy.

Solubility

76.4 g / 100 g of water at 25 ° C. 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 alcohol; that is, in solvents less polar than water.

Density

1.77 g / cm 3 at 25 ° C.

Vapor pressure

1,871 kPa at 20 ° C.

Flashpoint

26 ° C.

pH

5.0-6.0 (25 ° C. 1M solution). The slightly acidic pH is due to the hydrolysis of NH + in water, producing H 3 O + at low concentrations.

Stability

Stable in suitable environmental conditions. In contact with strong oxidants, it can ignite.

Decomposition

It begins to decompose at 150 ºC, releasing toxic fumes of sulfur oxide, nitrogen oxide, and ammonium.

Corrosion

It does not attack iron or aluminum.

Uses of ammonium sulfate

In the agriculture

  • Ammonium sulfate is used as a fertilizer in 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 concentration of sulfur.
  • Sulfur is essential in protein synthesis since several amino acids – such as cysteine, methionine, and cysteine ​​- have sulfur. For these reasons, ammonium sulfate continues to be one of the most important fertilizers.
  • It is used in the crops of wheat, corn, rice, cotton, potatoes, hemp, and fruit trees.
  • It lowers the pH of alkaline soils due to its contribution to the nitrification process carried out by microbes. Ammonium (NH + ) is used to produce nitrate (NO  ) and release H + : 2NH +  + 4O 2  => 2NO   + 2H 2 O + 4H + . Increasing the hydrogen concentration lowers the pH of alkaline soils and allows more use.
  • In addition to its use as a fertilizer, ammonium sulfate acts as an adjunct 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 necessary for certain pathogens’ life. Among the ions that ammonium sulfate captures are Ca 2+, Mg 2+, Fe 2+, and Fe 3+. This action enhances the microbicidal effect of the mentioned agents.

As an 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 ones. An amount of ammonium sulfate is added to the plasma to bring it to 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, precipitation of another group of proteins occurs.

The repetition of the previous process in a sequential way allows a result the obtaining of different fractions of plasmatic proteins.

Before the new technologies of molecular biology appeared, this procedure allowed the isolation of plasma proteins of great importance in medicine, for example, immunoglobulins, coagulation factors, etc.

In the industry

Ammonium sulfate acts by retarding the start of the fire in the textile industry. It is used as an additive in the electroplating industry. It is also used to produce hydrogen peroxide, ammonium chloride, etc.

Other uses

  • It is used as an osmotic pressure regulating agent and salt precipitating agent.
  • In the form of ammonium lauryl sulfate, it lowers the surface tension of the water, thus allowing the separation of contaminants by increasing the hardness of the water.
  • It is an anti-corrosion agent.
  • It is used as a food additive that regulates acidity in flour dough and bread.

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