By Chris Deziel – Updated Mar 24, 2022
The carbonate ion (CO₃²⁻) combines with alkali metals to form a variety of essential industrial and household compounds. Two of the most widely used are sodium carbonate (Na₂CO₃) – commonly known as soda ash or washing soda – and calcium carbonate (CaCO₃), the mineral form of calcite that makes up chalk, limestone, and marble.
While calcium carbonate is found naturally in marble, chalk, limestone, and even the shells of marine organisms, sodium carbonate is traditionally extracted from trona ore or the mineral nahcolite (a naturally occurring form of sodium bicarbonate). Heating these raw materials releases the desired salt.
In addition, industry can manufacture “synthetic soda ash” by reacting calcium carbonate with sodium chloride:
CaCO₃ + 2 NaCl → CaCl₂ + Na₂CO₃
This seven‑step process yields a high‑purity product that is used in a range of applications.
Both salts are basic. In a 10 mM aqueous solution, sodium carbonate exhibits a pH of 10.97, while calcium carbonate’s pH is 9.91. Sodium carbonate is moderately soluble in water and is a common pH‑adjuster in swimming pools and industrial processes.
Calcium carbonate’s solubility is low in pure water but increases in the presence of dissolved CO₂, which forms carbonic acid. This property underlies the natural erosion of limestone formations by rainwater.
Glass manufacturers rely on sodium carbonate as a flux; it lowers the melting point of silica, making glass production more energy‑efficient. In homes, soda ash is used for water softening, pool sanitation, and dye fixing.
Calcium carbonate’s primary uses are in construction: it serves as a mortar additive, a key component of drywall and joint compound, and a pigment in paint. Gardeners apply it as a soil pH balancer, and it is also found in many antacids and calcium supplements.
