CARBON DIOXIDE ABSORPTION BY ALCOHOLS 



179 



(8.9a) MgCO, (or CaCOs) ^f= 

 (8.9b) COr- + CO2 + HoO ^ 



Mg+^ (or Ca++) + CO3- 

 =^ 2 HCO3- 



(8.9) 



MgCOs (or CaCOa) + CO2 + H2O ^ 



=^ Mg++ (or Ca++) + 2 HCOr 



the dissolution of one mole of alkaline earth carbonate is coupled with the absorption 

 of one mole carbon dioxide from the air. The equihbrium (8.9) has been studied by 

 Tillmans and Heublein (1912), Auerbach (1912), Tillmans (1919, 1921), Johnston and 

 Wilhamson (1916), Frear and Johnston (1929), and Kline (1929). Table 8. VI contains 

 some results. 



Table 8.VI 

 Solubility of CO2 in Presence of Alkaline Earth Carbonates at 25° C. 



The "natural" concentration of bicarbonate ions in solution is 

 increased by the presence of calcium carbonate, by a factor of 500 in 

 air, and a factor of 140 in pure carbon dioxide. The effect of magnesium 

 carbonate is ten times stronger. One-half of this bicarbonate comes 

 from the solid salt and the other half from the atmosphere. 



The solubility of carbon dioxide in water is decreased by the presence 

 of electrolytes (salting-out effect). For salt concentrations found in 

 plant saps (~ 10~^ mole/liter), this depression may be of the order of 

 5-10% (cf. Quinn and Jones 1936, pp. 97 and 102). 



2. Carbon Dioxide Absorption by Alcohols 



Plants contain, in addition to aqueous phases (cell sap and cytoplasm), phases of a 

 predominantly "Upoid" character. Chloroplasts, in particular, are rich in hpoids. 

 The carbon dioxide distribution between atmosphere and plant cells can therefore be 

 affected by the solubility of carbon dioxide in hpoids. In general, carbon dioxide is 

 more soluble in organic solvents, than in water — 3 times more soluble in toluene and 

 benzene, 3.5 times more in ethanol, and 7.5 times more in acetone. In true lipids, 

 the solubiUty may well be even higher. 



The "physical" solution of carbon dioxide in organic solvents is often enhanced 

 by chemical reactions, analogous to hydration. As in water, the effect of chemical 

 solvation is small in pure solvents, but becomes large when occasion is given for the 

 formation of anions, analogous to the bicarbonate ions in water. 



In the case of alcohols, for example, the molecular solvation equilibrium 



(8.10) 0C=0 + ROH . OC— OH 



I 

 OR 



