Sulfate

Sulfates, salts or esters of sulfuric acid. The salts include the sulfate anion [ SO4 ] 2 - and the hydrogen sulfate anion [ HSO 4 ] -. The esters of sulfuric acid have the general formula R -O- SO2 -O- R ', this R and / or R' are organic radicals,

  • 2.1 General

Nomenclature

Primary and secondary sulfates

The salts of the dibasic acid is sulfuric acid (H2SO4 ) can be divided into sulfates and hydrogen sulfates (also referred to as primary and secondary sulfates ). For monovalent cations MI the sum formulas MIHSO4 and MI2SO4 apply:

Alums and vitriols

Alums are double salts of mono- and trivalent cations with the general empirical formula Mimiii ( SO4) 2 · H2O 12, the main representative of the group of alums is the potassium aluminum sulfate ( potassium alum ). Vitriols however, are the hydrated sulfates of divalent transition group metals ( copper sulphate, ferrous sulphate, etc.).

Sulfate complexes

Sulfate groups can occur in complexes as ligands. The ligands are referred to in this case as [ Tetraoxosulfato (-2 )] or [ sulfato (-2) ]. Following recommendations of the Nomenclature bear sulfite (SO3) 2 - the suffix- sulphate and as Trioxosulfat or [ Trioxosulfat (IV ) ] denotes.

Esters of sulfuric acid

Sulfuric acid esters are sometimes referred to as sulfates, because the names often end in- sulphate. Simple esters such as dimethyl sulfate are strong alkylating agent. Esters with longer hydrocarbon radicals and sulfonic acid salts are surfactants usually. These esters also include the important applications of fatty alcohol sulfates.

  • Monoester; For example, sodium lauryl sulfate, a surfactant which has been used in shampoos.
  • Diesters; For example, dimethyl sulfate, a reactant which is used in laboratory and technique for methylation.

Properties

General

Most sulfates are soluble in water. Exceptions are little or poorly soluble sulfates of alkaline earth metals calcium, strontium and barium, and lead (II ) sulfate.

In particular, the alkali and alkaline earth metal are thermally very stable. Sulfates of trivalent metal cations decompose in the heat to the corresponding oxides and sulfur trioxide:

Hydrogensulfates are known as salts of alkali metals. They are soluble in water. When heated, these salts are disulfates salts of disulphuric form.

Sulfuric acid is a strong dibasic acid. In a one molar aqueous solution of the acid are virtually no H2SO4 molecules, but essentially HSO 4 - ions. Only just over 1% of the HSO 4 - ion deprotonate to SO42 -. The bisulfate anion ( HSO4 - ) can act both as an acid and as a base, so it is amphoteric. The pKa value of the hydrogen sulfate ion is 1.89.

Once one bisulfate salt in water, is formed in an equilibrium reaction, a mixture of bisulfate and sulfate ions. Therefore, one can use hydrogen sulfates as moderately strong acid, the acid strength is significantly higher than that of acetic acid ( pKa = 4.76 ). Owing to these properties hydrogensulfates may be used in buffer solutions. The buffer area is located in the highly acidic range. Because of their acidic reaction in water, they are used for example in toilet cleaners.

Occurrence

Sulfates provide for many metallic elements, the most important mineral compounds dar. sources of sulfate in the soil rock are eg anhydrite (CaSO4 ), gypsum (CaSO4 · 2 H2O) and Alabaster (CaSO4 · 2 H2O). Biological source (bacterial ) sulphate formation of sulfide and sulfur-containing biomass constituents (eg proteins). Sulfates are present in varying amounts in groundwater. For drinking water obtained therefrom is considered by the German Drinking Water Regulation, a limit of 250 mg / l

Structure of the sulfate ion

The sulfate ion is built tetrahedral, the SO bonds are all of equal value and of equal length. The bonding can be described either by resonance structures with delocalized π - bonds and two negatively charged oxygen atoms or by charge separation with doubly positively charged sulfur atom and negative charge on each oxygen atom. It is isoelectronic with the perchlorate ion. From the molecular orbital diagram showing how the binding and hypervalency can be explained. It is assumed with four singly occupied atomic orbitals a doubly positively charged sulfur atom. These orbitals are combined with four singly occupied 2p orbitals of the singly negatively charged oxygen atoms. There arise four binding four and σ antibonding orbitals, of which only the bonding are completely filled, and thus the tetrahedral molecular structure with four localized single bonds. The unoccupied antibonding? P * orbitals are then combined with one fully occupied p orbital of three oxygen atoms, there arise three bonding and three antibonding π orbitals, of which again only the bonding orbitals are occupied. This results in three π - bonds, which are on the whole molecule, ie via the sulfur atom and all four oxygen atoms, delocalized.

Proof

Sulfates are detected chemically with barium chloride or barium hydroxide solution in hydrochloric acid. The result is a sparingly soluble precipitate of white barium sulfate:

The acid is added to reduce interference, since other anions such as carbonate or sulfite form with barium in water also poorly soluble but soluble in acids salts.

In water analysis, see also titrimetric method application for the quantitative determination.

Examples

  • Alum ( potassium aluminum sulfate, KAl (SO4) 2 · 12 H 2 O, and other alums, such as ammonium iron ( III) sulphate )
  • Aluminite ( Al 2 [( OH) 4SO4 ] · 7 H2O, a mineral )
  • Anhydrite (calcium sulfate, CaSO4, crystal water free - with crystal water as gypsum, white, insoluble in water - see below)
  • Lead (II ) sulfate ( PbSO4, formed by sulfuric acid acting on the lead plates in car batteries, white, insoluble in water )
  • Calcium aluminate, Ca6Al2 [( OH) 12 | (SO4 ) 3] · 26 H2O
  • Barite ( barium sulfate, BaSO4 )
  • Alum (potassium chromium sulfate hydrate, chromium ( III) potassium sulfate dodecahydrate, KCr ( SO4) 2 · 12 H2O) and similar alums
  • Cobalt (II ) sulfate ( CoSO4 · 7 H2O, a vitriol )
  • Gypsum ( hydrous calcium sulfate, CaSO4 · 2 H2O) and Alabaster ( crystalline calcium sulfate)
  • Iron (II ) sulfate ( FeSO4 ) Iron vitriol of crystallization also called green vitriol
  • Potassium hydrogen sulfate ( ( KHSO 4 ), as acid drain cleaners on the market)
  • Levosalbutamol · sulfate (CAS No. 148563-16-0 ), the salt of a basic amine
  • Magnesium sulfate ( MgSO4 ) of crystallization also known as Epsom salt
  • Manganese (II ) sulfate ( MnSO4, of crystallization also called Manganvitriol, pale pink )
  • Mohr's salt, also: Ammonium iron (II ) sulfate, a bright green double salt of ammonium and iron (II ) sulfate
  • Referred sodium sulfate ( Na2SO4) of crystallization as Glauber's salt
  • Sodium hydrogen sulfate ( NaHSO 4 )
  • Nickel sulfate ( NiSO4 ) of crystallization also called Nickel sulfate, green
  • Copper (II ) sulfate, also known as blue vitriol of crystallization, light blue
  • Zinc sulphate ( ZnSO4 · 7 H2O, zinc vitriol )

Prototypes of vitriols, alums and other sulfates are:

Lead(II) sulfate Equilibrium constant Hypervalent molecule Water chemistry analysis Baryte Chrome alum Cobalt(II) sulfate Manganese(II) sulfate Iron(III) sulfate
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