Sodium carbonate Na2CO3 soda

Sodium carbonate decahydrate, Na2CO3-10H2O, was once widely used as washing soda. It is still sometimes added to water to precipitate Mg2+ and Ca2+ ions as carbonates, as in... 

If you wish, you can remove some of these ions (mainly Ca2+(aq), Mg2+(aq), and Fe2+(aq)) yourself. For relatively small volumes of water (such as enough to fill a bathtub or a washing machine), you can add sodium carbonate decahydrate, Na2CO3-10H2O. This compound is commonly called washing soda. It is an inexpensive way to add carbonate ion to the water. The carbonate ions precipitate the unwanted ions. 

Sodium carbonate, Na2C03, is a white, crystalline solid known commercially as soda ash. Large amounts of soda ash are used in the manufacture of glass. The hydrated compound, Na2CO3-10H2O,is known as washing soda. 

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