8 



PROPERTIES OF SOLUTIONS 



of organisms — in oceans, lakes, streams, soils, and raindrops — also contains 

 these gases in solution, and sometimes others as well. 



A given volume of water or any other liquid will hold only a limited 

 quantity of gas in solution at a given temperature. When no more of a 

 certain gas can be dissolved in a liquid it is said to be saturated with respect 

 to that gas. Gases vary widely in their solubility in water, but in general fall 

 into two groups: those which are sparingly soluble, and those which are 

 highly soluble. When only a small fraction of a unit volume of a gas will 

 dissolve in a unit volume of water the gas is classified in the sparingly soluble 

 group. When from one to many unit volumes of a gas will dissolve in one 

 unit volume of water it is classified in the highly soluble group. 



Oxygen, hydrogen, and nitrogen are familiar examples of gases belonging 

 to the first group, while carbon dioxide, ammonia, and hydrogen chloride are 

 examples of the second. When gases are highly soluble in water it is usually 

 evidence that a chemical reaction takes place between the gas and water. The 

 reactions between water and carbon dioxide and water and ammonia are 

 indicated in the following equations : 



CO2 + H2O 

 NH3 + H2O 



H2CO3 

 NH4OH 



In a solution of such gases not only are molecules of the gas present, but 

 also molecules of a compound formed by the reaction of the gas with water. 

 The apparently great solubility of gases such as these is due to the forma- 

 tion of relatively soluble compounds by the reaction of the gas with the 

 water. The solubilities of some common gases in water are shown in Table i. 



TABLE I SOLUBILITY OF SOME COMMON GASES IN WATER AT DIFFERENT TEMPERATURES 



WHEN THE PRESSURE OF THE GAS IS ONE ATMOSPHERE. 



Gas 



Carbon Dioxide 



Oxygen 



Nitrogen 



Hydrogen 



Volume of gas dissolved in one volume of 

 water (reduced to standard conditions) 



ID 



1. 194 

 o. 03 80 

 0.0186 

 0.0195 



20° C. 



0.878 

 0.0310 

 0.0154 

 0.0182 



30° c. 



0.665 

 0.0261 



0.0134 



0.0170 



In general, as also shown in Tabic i, an increase in temperature decreases 

 the solubility of a gas in a liquid. 



