Salts of oxoacids carbonates and hydrogencarbonates

The alkali metal oxides, peroxides and superoxides react with water according to equations 10.11-10.13. One use of KO2 is in breathing masks where it absorbs H2O producing O2 for respiration and KOH, which absorbs exhaled CO2 (reaction 10.14). 

Sodium peroxide reacts with CO2 to give Na2C03, rendering it suitable for use in air purification in confined spaces (e.g. in submarines) KO2 acts similarly but more effectively. 

Although all the group 1 peroxides decompose on heating according to equation 10.15, their thermal stabilities depend on cation size Li202 is the least stable peroxide, while CS2O2 is the most stable. The stabilities of the superoxides (with respect to decomposition to M2O2 and O2) follow a similar trend. 

Ozonides, MO3, containing the paramagnetic, bent [03] ion (see Section 15.4), are known for all the alkali metals. The salts KO3, Rb03 and CSO3 can be prepared from the peroxides or superoxides by reaction with ozone, but this method fails, or gives low yields, for LiOs and NaOs. These ozonides have recently been prepared in liquid ammonia by the interaction of CSO3 with an ion-exchange resin loaded with either Li or Na ions. The ozonides are violently explosive. 

An ion-exchange resin consists of a solid phase (e.g. a zeolite) which contains acidic or basic groups which may exchange with cations or anions, respectively, from solutions washed through the resin an important application is in water purification (see Box 15.3). 

The properties of alkali metal salts of most oxoacids depend on the oxoanion present and not on 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 Li2C03 is sparingly soluble in water, the remaining carbonates of the group 1 metals are very soluble. 

The chloralkali industry produces huge quantities of NaOH and CI2 by the electrolysis of aqueous NaCl (brine). 

Note that the anode discharges CI2 rather than O2 even though, from values of it appears easier to oxidize H2O than CN. This observation is a consequence of the overpotential required to release O2 and is explained more fully in worked example 17.3. 

Aqueous NaOH from the electrolytic process is evaporated to give solid NaOH (caustic soda) as a white, translucent solid 

A technician checking mercury cells in the cell room of a plant producing CI2 and NaOH. 

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