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Sodium sulfate

2007 Schools Wikipedia Selection. Related subjects: Chemical compounds

                           Sodium sulfate
                           Sodium sulfate

                               General
    Systematic name                                    Sodium sulfate
        Other names                      Sodium sulphate
                                           Salt cake
                                         Thenardite (mineral)
                                         Glauber's salt (decahydrate)
                                         Sal mirabilis (decahydrate)
                                         Mirabilite (decahydrate)
                                                                Trona
  Molecular formula                                        Na[2]SO[4]
           Hydrates                  Heptahydrate: Na[2]SO[4]·7H[2]O
                                      Decahydrate: Na[2]SO[4]·10H[2]O
         Molar mass           142.04214 g/mol ( anhydrous)
                              268.14924 g/mol (heptahydrate
                                        322.19514 g/mol (decahydrate)
         Appearance                          White crystalline solid,
                                                          hygroscopic
         CAS number                           [7757-82-6] (anhydrous)
                                            [7727-73-3] (decahydrate)
                             Properties
            Density                    2.68 g/cm^3, anhydrous
                                       (orthorhombic form)
                                            1.464 g/cm^3, decahydrate
Solubility in water                             4.76 g/100 ml (0 °C)
                                               42.7 g/100 ml (100 °C)
         In ethanol                                         insoluble
      Melting point                        884 °C (1157 K) anhydrous
                                                  32.4 °C decahydrate
                              Structure
       Coordination
           geometry                                                 ?
  Crystal structure                       monoclinic, orthorhombic or
                                                            hexagonal
                               Hazards
               MSDS                                     External MSDS
       Main hazards                                          Irritant
      R/S statement                                              None
       RTECS number                             WE1650000 (anhydrous)
           NFPA 704

                    0
                    2
                    0

                       Supplementary data page
      Structure and
         properties                                     n, ε[r], etc.
      Thermodynamic
               data                                   Phase behaviour
                                                   Solid, liquid, gas
      Spectral data                                   UV, IR, NMR, MS
                          Related compounds
       Other anions              Sodium hydrogen sulfate
                                          Sodium sulfite
                                        Sodium bisulfite
                                                    Sodium persulfate
      Other cations                     Lithium sulfate
                                        Potassium sulfate
                                                    Magnesium sulfate
          Except where noted otherwise, data are given for
                materials in their standard state (at 25°C, 100 kPa)
                                    Infobox disclaimer and references

   Sodium sulfate is an important compound of sodium. When anhydrous, it
   is a white crystalline solid of formula Na[2]SO[4]. The deca hydrate,
   Na[2]SO[4]•10H[2]O, is known as Glauber's salt. Sodium sulfate is
   mainly used for the manufacture of detergents and in the Kraft process
   of paper pulping, although it has many other uses. About half of the
   world's production is from the natural mineral form of the decahydrate
   (mirabilite), and half from by-products of chemical processes.

History

   Glauber's salt, the decahydrate also known as sal mirabilis, is named
   after Johann Glauber, who discovered it in the 17th century. The white
   or colorless crystals were originally used as a laxative.

Physical and chemical properties

   Na[2]SO[4] is chemically very stable, being unreactive toward most
   oxidising or reducing agents at normal temperatures. At high
   temperatures, it can be reduced to sodium sulfide. It is a neutral
   salt, which forms aqueous solutions with pH of 7. The neutrality such
   solutions reflects the fact that Na[2]SO[4] is derived, formally
   speaking, from a strong acid (sulfuric acid) and a strong base (sodium
   hydroxide). Sodium sulfate reacts with an equivalent amount of sulfuric
   acid to give an equilibrium concentration o the acid salt sodium
   hydrogen sulfate:

          Na[2]SO[4]( aq) + H[2]SO[4](aq) → 2 NaHSO[4](aq)

   In fact the equilibrium is very complex and dependent on concentration
   and temperature, with other acid salts being present.

   Na[2]SO[4] is a typical ionic sulfate, containing Na^+ ions and
   SO[4]^2− ions. Aqueous solutions can produce precipitates when combined
   with salts of Ba^2+ or Pb^2+, which form insoluble sulfates:

   Na[2]SO[4](aq) + BaCl[2](aq) → 2 NaCl(aq) + BaSO[4]( s)

   Sodium sulfate has unusual solubility characteristics in water, ^3 as
   shown in the graph below. Its solubility rises more than tenfold
   between 0 °C to 32.4 °C, where it reaches a maximum of 49.7 g
   Na[2]SO[4]per 100 g water. At this point the solubility curve changes
   slope, and the solubility becomes almost independent of temperature. In
   the presence of NaCl, the solubility of Na[2]SO[4] is markedly
   diminished. Such changes provide the basis for the use of sodium
   sulfate in passive solar heating systems, as well is in the preparation
   and purification of sodium sulfate.
   Graph showing solubility of Na2SO4 vs. temperature

   This nonconformity can be explained in terms of hydration, since 32.4
   °C corresponds with the temperature at which the crystalline
   decahydrate (Glauber's salt) changes to give a sulfate liquid phase and
   an anhydrous solid phase.

Occurrence

   About half of the world's production of the decahydrate (Glauber's
   salt) is from the natural mineral form mirabilite - found in lake beds
   in southern Saskatchewan, for example. In 1990, Mexico and Spain were
   the world's main producers of natural sodium sulfate (each around 500
   000 tonnes), with USSR, USA and Canada also important (around 350 000
   tonnes each).

   Anhydrous sodium sulfate occurs in arid environments as the mineral
   thenardite, which is less common than mirabilite. It slowly turns to
   mirabilite in damp air.

Manufacture

   About half of the world's sodium sulfate comes from natural sources
   (see above), while the other half is produced as a by-product of other
   processes. The most important of these is the production of
   hydrochloric acid from sodium chloride (salt) and sulfuric acid (the
   Mannheim process), in which case the Na[2]SO[4] is known as salt cake:

          2 NaCl + H[2]SO[4] → Na[2]SO[4] + 2 HCl

   Alternatively, Na[2]SO[4] can be produced from sulfur dioxide using the
   Hargreaves process:

          4 NaCl + 2 SO[2] + O[2] + 2 H[2]O → 2 Na[2]SO[4] + 4 HCl

   In the US and UK, Na[2]SO[4] is as a major by-product of the
   manufacture of sodium dichromate. Other sources of Na[2]SO[4] include a
   myriad of processes where leftover sulfuric acid is neutralised by
   sodium hydroxide. This method is also the most convenient laboratory
   preparation.

          2 NaOH( aq) + H[2]SO[4](aq) → Na[2]SO[4](aq) + 2 H[2]O( l)

   Bulk sodium sulfate is usually purified via the decahydrate form, since
   the anhydrous form tends to attract iron compounds and organic
   compounds. The anhydrous form is easily produced from the hydrated form
   by gentle warming.

Uses

   In 1995, bulk sodium sulfate sold for around $70 per tonne in the US,
   making it a very cheap material. Probably the largest use for sodium
   sulfate today is as a filler in powdered home laundry detergents. Total
   consumption of Na[2]SO[4] in Europe was around 1.6 million tonnes in
   2001, of which 80% was used for detergents. However this use is waning
   as domestic consumers are increasingly switching to liquid detergents
   that do not include the chemical.

   Another major use for Na[2]SO[4], particularly in the US, is in the
   Kraft process for the manufacture of wood pulp. Organics present in the
   "black liquor" from this process are burnt to produce heat, needed to
   drive the reduction of sodium sulfate to sodium sulfide. However, this
   process is being replaced to some extent by newer processes; use of
   Na[2]SO[4] in the US pulp industry declined from 980 000 tonnes in 1970
   to only 210 000 tonnes in 1990.

   The glass industry also provides another significant application for
   sodium sulfate, consuming around 30 000 tonnes in the US in 1990 (4% of
   total US consumption). It is used as a "fining agent", to help remove
   small air bubbles from molten glass. It also fluxes the glass, and
   prevents scum formation of the glass melt during refining.

   Sodium sulfate is important in the manufacture of textiles,
   particularly in Japan. It helps in "levelling", reducing negative
   charges on fibres so that dyes can penetrate evenly. Unlike the
   alternative sodium chloride, it does not corrode the stainless steel
   vessels used in dyeing.

   Glauber's salt, the decahydrate, was formerly used as a laxative. It
   has also been proposed for heat storage in passive solar heating
   systems.^6 This takes advantage of the unusual solubility properties
   (see above), and the high heat of crystallisation (78.2 kJ/mol). Other
   uses for sodium sulfate include frosting windows, in carpet fresheners,
   starch manufacture and as an additive to cattle feed. In the
   laboratory, anhydrous sodium sulfate is widely used as an inert drying
   agent for organic solutions; Na[2]SO[4] is added to the solution until
   the crystals no longer clump together.

Precautions

   Although sodium sulfate is generally regarded as non-toxic, handle it
   with care.

Suppliers/Manufacturers

     * Elementis Chromium
     * Meishan Dongpo District Yinfeng Chemical Co.
     * Cooper
     * Great LakesMinerals Co.
     * Chinatrona

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