ammonium sulfate

Ammonium sulfate
IUPAC name	Ammonium sulfate
Other names	ammonium sulfate (2:1) diammonium sulfate sulfuric acid diammonium salt mascagnite Actamaster Dolamin
Identifiers
CAS number	7783-20-2 Y
SMILES	O=S(=O)(O)O.N.N
InChI	1/2H3N.H2O4S/c;;1-5(2,3)4/h2*1H3;(H2,1,2,3,4)
InChI key	BFNBIHQBYMNNAN-UHFFFAOYAI
ChemSpider ID	22944
Properties
Molecular formula	(NH4)2SO4
Molar mass	132.14 g/mol
Appearance	Fine white hygroscopic granules or crystals.
Density	1.769 g/cm3 (20 °C)
Melting point	235-280 °C, 508-553 K, 455-536 °F (decomposes)
Solubility in water	70.6 g/100 mL (0 °C) 74.4 g/100 mL (20 °C) 103.8 g/100 mL (100 °C)[1]
Solubility	insoluble in acetone, alcohol and ether
Critical relative humidity	79.2% (30 °C)
Hazards
EU Index	Not listed
NFPA 704	1 2 0
Flash point	Non-flammable
LD50	2840 mg/kg, rat (oral)
Related compounds
Other anions	Ammonium thiosulfate Ammonium sulfite Ammonium bisulfate Ammonium persulfate
Other cations	Sodium sulfate Potassium sulfate
Related compounds	Ammonium iron(II) sulfate
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Ammonium sulfate (IUPAC-recommended spelling; also ammonium sulphate in British English), (NH₄)₂SO₄, is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen as ammonium cations, and 24% sulfur as sulfate anions. In fertilizer the purpose of the sulfate is to reduce the soil pH.

Uses

It is used largely as an artificial fertilizer for alkaline soils. In the soil the sulfate ion is released and forms bisulfate, lowering the pH balance of the soil (as do other sulfate compounds such as aluminium sulfate), while contributing essential nitrogen for plant growth.

It is also used as an agricultural spray adjuvant for water soluble insecticides, herbicides, and fungicides. There it functions to bind iron and calcium cations that are present in both well water and plant cells. It is particularly effective as an adjuvant for 2,4-D (amine), glyphosate, and glufosinate herbicides.

It is also used in the preparation of other ammonium salts.

In biochemistry, ammonium sulfate precipitation is a common method for purifying proteins by precipitation. As such, ammonium sulfate is also listed as an ingredient for many United States vaccines per the Center for Disease Control.^[2]

Ammonium sulfate is also a food additive.^[3][4]

A saturated solution of ammonium sulfate in heavy water (D₂O) is used as an external standard in sulfur (³³S) NMR spectroscopy with shift value of 0 ppm.

It has also been used in flame retardant compositions acting much like Diammonium phosphate. As a flame retardant, it lowers the combustion temperature of the material, decreases maximum weight loss rates, and causes an increase in the production of residue or char.^[5]

Preparation

Ammonium sulfate is made by reacting synthetic ammonia (or by-product ammonia from coke-ovens) with sulfuric acid:^[6]

2 NH₃ + H₂SO₄ → (NH₄)₂SO₄

A mixture of ammonia gas and water vapor is introduced into a reactor that contains a saturated solution of ammonium sulfate and about 2 to 4% of free sulfuric acid at 60 °C. Concentrated sulfuric acid is added to keep the solution acidic, and to retain its level of free acid. The heat of reaction keeps reactor temperature at 60 °C.

Dry, powdered ammonium sulfate may be formed by spraying sulfuric acid into a reaction chamber filled with ammonia gas. The heat of reaction evaporates all water present in the system, forming a powdery salt.

Ammonium sulfate also is manufactured from gypsum (CaSO₄·2H₂O). Finely divided gypsum is added to an ammonium carbonate solution. Calcium carbonate precipitates out, leaving ammonium sulfate in the solution.

(NH₄)₂CO₃ + CaSO₄ → (NH₄)₂SO₄ + CaCO₃

Ammonium sulfate occurs naturally as the rare mineral mascagnite in volcanic fumaroles and due to coal fires on some dumps.^[7]

Reactions

Ammonium sulfate decomposes upon heating at 100 °C in an open system, forming ammonium bisulfate. As a salt of a strong acid (i.e. H₂SO₄) and weak base (i.e. NH₃), its solution is acidic; pH of 0.1M solution is 5.5.

In aqueous solution the reactions are those of NH₄⁺ and SO₄⁻² ions. For example, addition of barium chloride, precipitates out barium sulfate. The filtrate on evaporation yields ammonium chloride.

Ammonium sulfate forms many double salts (ammonium metal sulfates) when its solution is mixed with equimolar solutions of metal sulfates and the solution is slowly evaporated. Such double metal sulfates include ammonium cobaltous sulfate, ferric ammonium sulfate, ammonium nickel sulfate and ammonium cerous sulfate. ^[6]

References

Further reading

• Properties: UNIDO and International Fertilizer Development Center (1998), Fertilizer Manual, Kluwer Academic Publishers, ISBN 0-7923-5032-4.