Editing Sodium carbonate (section)

==Hydrates==
Sodium carbonate is obtained as three [[hydrate]]s and as the anhydrous salt:
* sodium carbonate decahydrate ([[natron]]), Na<sub>2</sub>CO<sub>3</sub>·10H<sub>2</sub>O, which readily [[efflorescence|effloresces]] to form the monohydrate.
* sodium carbonate heptahydrate (not known in mineral form), Na<sub>2</sub>CO<sub>3</sub>·7H<sub>2</sub>O.
* sodium carbonate monohydrate ([[thermonatrite]]), Na<sub>2</sub>CO<sub>3</sub>·H<sub>2</sub>O. Also known as '''crystal carbonate'''.
* anhydrous sodium carbonate (natrite), also known as calcined soda, is formed by heating the hydrates. It is also formed when sodium hydrogencarbonate is heated (calcined) e.g. in the final step of the [[Solvay process]].
The decahydrate is formed from water solutions crystallizing in the temperature range −2.1 to +32.0&nbsp;°C, the heptahydrate in the narrow range 32.0 to 35.4&nbsp;°C and above this temperature the monohydrate forms.<ref>{{cite journal|title=On the transition temperatures of the transition temperatures of the hydrates of sodium carbonate as fix points in thermometry |journal=Journal of the American Chemical Society |volume=36 |issue=3 |pages=485–490 |author= T.W.Richards and A.H. Fiske|doi=10.1021/ja02180a003 |year=1914 |url=https://zenodo.org/record/1428987}}</ref> In dry air the decahydrate and heptahydrate lose water to give the monohydrate. Other hydrates have been reported, e.g. with 2.5 units of water per sodium carbonate unit ("Penta hemihydrate").<ref>{{cite web |url=http://www.minsocam.org/ammin/am15/am15_69.pdf |author=A. Pabst |title=On the hydrates of sodium carbonate }}</ref>

===Washing soda===
Sodium carbonate decahydrate (Na<sub>2</sub>CO<sub>3</sub>·10H<sub>2</sub>O), also known as washing soda, is the most common hydrate of sodium carbonate containing 10 molecules of [[water of crystallization]]. Soda ash is dissolved in water and crystallized to get washing soda.

:{{chem2 | Na2CO3 + 10 H2O -> Na2CO3*10H2O }}

It is one of the few metal [[carbonate]]s that is soluble in water.