It most commonly occurs as a crystalline decahydrate, which readily effloresces to form a white powder, the monohydrate. Pure sodium carbonate is a white, odorless powder that is hygroscopic -absorbs moisture from the air.

It has a strongly alkaline taste, and forms a moderately basic solution in water. Sodium carbonate is well known domestically for its everyday use as a water softener. Historically it was extracted from the ashes of plants growing in sodium-rich soils, such as vegetation from the Middle East, kelp from Scotland and seaweed from Spain.

Because the ashes of these sodium-rich plants were noticeably different from ashes of timber -used to create potash-, they became known as 'soda ash'. It is synthetically produced in large quantities from salt -sodium chloride- and limestone by a method known as the Solvay process. The manufacture of glass is one of the most important uses of sodium carbonate. Sodium carbonate acts as a flux for silica, lowering the melting point of the mixture to something achievable without special materials. This 'soda glass' is mildly water-soluble, so some calcium carbonate is added to the melt mixture to make the glass produced insoluble. This type of glass is known as soda lime glass: 'soda' for the sodium carbonate and 'lime' for the calcium carbonate. Soda lime glass has been the most common form of glass for centuries.

Sodium carbonate is also used as a relatively strong base in various settings. For example, it is used as a pH regulator to maintain stable alkaline conditions necessary for the action of the majority of photographic film developing agents.

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