What Is Solubility of Sodium Carbonate in Water?

Sodium Carbonate "Washing Soda"

Sodium carbonate--Na₂CO₃·7H₂O--is derived from the reaction between carbonic acid and sodium hydroxide. Because carbonic acid is a weak acid and sodium hydroxide is a strong base, sodium carbonate is a basic salt. The reaction is:

2NaOH + H₂CO₃ ' Na₂CO₃ + 2H₂O

Electropositive Sodium

Sodium metal is very electropositive. It readily gives up its outermost electron to form the ion Na⁺. Sodium thus forms ionic, not covalent, bonds. Sodium carbonate in water splits into ions.

Sodium Ions

Sodium ions have an aqueous coordination number of four. This means each sodium ion will be surrounded by four water molecules. This lessens charge density because the charge migrates across eight hydrogen atoms.

Empirical Results

Empirically, sodium carbonate's solubility in water is 216 grams/liter of water at 20 degrees Celsius. This is the maximum amount that will dissolve. Such a solution is "saturated."

Molarity

The chemist likes to speak in terms of molarity, which is the number of grams dissolved in one liter of water, divided by the molecular weight. In those terms, a saturated solution of sodium carbonate is 2.0 molar.

Uses

Such a concentrated solution of a strong base is useful in many ways. Historically, sodium carbonate, also called soda ash and washing soda, was used to make soap and to clean laundry.

The largest application of solid sodium carbonate is in glass manufacturing.

References

• Science Direct: Coordination numbers of alkali metal ions in aqueous solutions

Resources

• The Greenhouse: "Washing Soda"