naoh + al(oh)3

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Sodium aluminate

Crystal structure with sodium in yellow, aluminium in grey, and oxygen in red[1]

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Sodium metaaluminate sample

IUPAC name

Sodium aluminate

Other names

Sodium aluminium oxide,
Sodium metaaluminate
Aluminate, ((AlO2)1−), sodium


CAS Number

  • 1302-42-7 check

3D model (JSmol)

  • Interactive image
ECHA InfoCard 100.013.728 Edit this at Wikidata
EC Number
  • 215-100-1

PubChem CID

  • 14766
  • 2VMT26903W check

CompTox Dashboard (EPA)

  • DTXSID90872314 DTXSID3051206, DTXSID90872314 Edit this at Wikidata


  • InChI=1S/Al.Na.2O/q-1;+1;;



  • O=[Al-]=O.[Na+]


Chemical formula

Molar mass 81.97 g/mol
Appearance white powder (sometimes light-yellowish)
hygroscopic/ when dissolved in water a colloidal Đen solution is formed
Odor odorless
Density 1.5 g/cm3
Melting point 1,650 °C (3,000 °F; 1,920 K)

Solubility in water

highly soluble
Solubility Insoluble in alcohol[2]

Refractive index (nD)

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Crystal structure


Heat capacity (C)

73.6 J/mol K

Std molar
entropy (S298)

70.4 J/mol K

Std enthalpy of
formation fH298)

-1133.2 kJ/mol

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

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Infobox references

Sodium aluminate is an inorganic chemical that is used as an effective source of aluminium hydroxide for many industrial and technical applications. Pure sodium aluminate (anhydrous) is a white crystalline solid having a formula variously given as NaAlO2, NaAl(OH)4 (hydrated),[3] Na2O·Al2O3, or Na2Al2O4. Commercial sodium aluminate is available as a solution or a solid.
Other related compounds, sometimes called sodium aluminate, prepared by reaction of Na2O and Al2O3 are Na5AlO4 which contains discrete AlO45− anions, Na7Al3O8 and Na17Al5O16 which contain complex polymeric anions, and NaAl11O17, once mistakenly believed vĩ đại be β-alumina, a phase of aluminium oxide.[4][5]


Anhydrous sodium aluminate, NaAlO2, contains a three-dimensional framework of corner linked AlO4 tetrahedra. The hydrated khuông NaAlO2·5/4H2O has layers of AlO4 tetrahedra joined into rings and the layers are held together by sodium ions and water molecules that hydrogen bond vĩ đại O atoms in the AlO4 tetrahedra.[6]


Sodium aluminate is manufactured by the dissolution of aluminium hydroxide (Al(OH)3) in a caustic soda (NaOH) solution. Aluminium hydroxide (gibbsite) can be dissolved in 20–25% aqueous NaOH solution at a temperature near the boiling point. The use of more concentrated NaOH solutions leads vĩ đại a semi-solid product. The process must be carried out in steam-heated vessels of nickel or steel, and the aluminium hydroxide should be boiled with approximately 50% aqueous caustic soda until a pulp forms. The final mixture has vĩ đại be poured into a tank and cooled; a solid mass containing about 70% NaAlO2 then forms. After being crushed, this product is dehydrated in a rotary oven. The resulting product contains 90% NaAlO2 and 1% water, together with 1% không lấy phí NaOH.

Reaction of aluminium metal and alkali[edit]

Sodium aluminate is also formed by the action of sodium hydroxide on elemental aluminium which is an amphoteric metal. The reaction is highly exothermic once established and is accompanied by the rapid evolution of hydrogen gas. The reaction is sometimes written as:

2Al + 2NaOH + 2H2O → 2NaAlO2 + 3H2

However, the species produced in solution is likely vĩ đại contain the [Al(OH)4] ion or perhaps the [Al(H2O)2(OH)4] ion.[7]


In water treatment it is used as an adjunct vĩ đại water softening systems, as a coagulant aid vĩ đại improve flocculation, and for removing dissolved silica and phosphates.

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In construction technology, sodium aluminate is employed vĩ đại accelerate the solidification of concrete, mainly when working during frost.

Sodium aluminate is also used in the paper industry, for fire brick production, alumina production and so sánh forth.

Sodium aluminate solutions are intermediates in the production of zeolites.[8][9]


  1. ^ Kaduk, James A.; Pei, Shiyou (1995). "The Crystal Structure of Hydrated Sodium Aluminate, NaAlO2•5/4H2O, and Its Dehydration Product". Journal of Solid State Chemistry. 115 (1): 126–139. doi:10.1006/jssc.1995.1111.
  2. ^ The Merck Index. 10th ed. Rahway, New Jersey: Merck Co., Inc., 1983., p. 1229
  3. ^ "Aluminium".
  4. ^ "Identification and characterisation of three novel compounds in the sodium–aluminium–oxygen system", Marten G. Barker, Paul G. Gadd and Michael J. Begley, J. Chem. Soc., Dalton Trans., 1984, 1139–1146, doi:10.1039/DT9840001139
  5. ^ Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN 0-12-352651-5
  6. ^ "The Crystal Structure of Hydrated Sodium Aluminate, NaAlO2·5/4H2O, and Its Dehydration Product", James A. Kaduk, Shiyou Pei, Journal of Solid State Chemistry, 115, 1, 1995, 126–139, doi:10.1006/jssc.1995.1111
  7. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  8. ^ Lankapati, Henilkumar M.; Lathiya, Dharmesh R.; Choudhary, Lalita; Dalai, Ajay K.; Maheria, Kalpana C. (2020). "Mordenite-Type Zeolite from Waste Coal Fly Ash: Synthesis, Characterization and Its Application as a Sorbent in Metal Ions Removal". ChemistrySelect. 5 (3): 1193–1198. doi:10.1002/slct.201903715. S2CID 213214375.
  9. ^ Alan Dyer, (1994), Encyclopedia of Inorganic Chemistry, R. Bruce King (ed.), John Wiley & Sons, ISBN 0-471-93620-0

See also[edit]

  • Bayer process
  • Bauxite