carbonates and hydrogencarbonates of group 1 metals

     The properties of alkali metal salts of most oxoacids depend on the oxoanion present and not onm the cation; thus we tend to discuss salts of oxoacids under the appropriate acid. However, we single out the carbonates and hydrogencarbonates because of their importance. Whereas Li₂CO₃ is sparingly soluble in water, the remaining carbonates of the group 1 metals are very soluble.

In many countries, sodium carbonate (soda ash) and sodium hydrogencarbonate (commonly called sodium bicarbonate) are manufactured by the Solvay process (Figure 1.1), but this is being superseded where natural sources of the mineral trona, Na₂ CO₃.NaHCO₃.2H₂O, are available. Figure 1.1 shows that NH₃ can be recycled, but most waste CaCl₂ is dumped (e.g. into the sea) or used in winter road clearance. In 2001, ^_35 Mt of sodium carbonate was produced worldwide, 10.3Mt in the US. The US (a net exporter of Na₂CO₃) consumed ^_6.4 Mt of sodium carbonate in 2003; uses are summarized in Figure 1.2.

Sodium hydrogencarbonate, although a direct product in the Solvay process, is also manufactured by passing CO₂ through aqueous Na₂CO₃ or by dissolving trona in H₂O saturated with CO₂. Its uses include those as a foaming agent, a food additive (e.g. baking powder) and an effervescent in pharmaceutical products. The Solvay company has now developed a process for using NaHCO₃ in pollution control, e.g. by neutralizing SO₂ or HCl in industrial and other waste emissions.

     There are some notable differences between Na‏ and other alkali metal [CO₃]^2- and [HCO₃]^- salts. Whereas NaHCO₃ can be separated in the Solvay process by precipitation, the same is not true of KHCO₃. Hence, K₂CO₃ is produced, not via KHCO₃, but by the reaction of KOH with CO₂; K₂CO₃ has uses in the manufacture of certain glasses and ceramics. Among its applications, KHCO₃ is used as a buffering agent in water treatment and wine production. Lithium carbonate is only sparingly soluble in water; ‘LiHCO₃’ has not been isolated. The thermal stabilities of the group 1 metal carbonates with  increase down the group as r_M+‏ increases, lattice energy being a crucial factor. Such a trend in stability is common to all series of oxo-salts of the alkali metals.

The solid state structures of NaHCO₃ and KHCO₃ exhibit hydrogen bonding . In KHCO₃, the anions associate in pairs  whereas in NaHCO₃, infinite chains are present. In each case, the hydrogen bonds are asymmetrical. Sodium silicates are also of great commercial importance: