194 NON-METALS AND THEIR COMBINATIONS. 



KC1 ^K- +Cl'j Xaa 

 NaN0 3 ^ N0' 3 + Na- J 



It 

 KN0 3 



Evidently molecules of four products will be present in this mixture, 

 and likewise in all similar ones. If all the products are readily solu- 

 ble and of large dissociating power, and the solution is rather dilute, 

 there are few undissociated molecules present. The mixture then is 

 practically a mixture of ions, and nothing can be observed by the 

 eye to have taken place. But if one of the new products is " insolu- 

 ble" in water, there are more of its ions present than can be main- 

 tained in a saturated solution of the same, the excess of ions unite to 

 form molecules, and the excess of molecules are removed by precipi- 

 tation. In this way one factor in the equilibrium is removed and the 

 action runs to completion. This principle is at the basis of all cases 

 of precipitation in chemical reactions. The precipitation of silver 

 chloride is a good example, and is represented thus : 



It 



NaN0 3 soluble. 



A simple equation, in which only the ions are represented, may be 

 used : 



Ag- + NO S ' + Na- + Cl' = AgCl 4- Na' 4- NO 3 '. 



The simplest equation of all is one which shows only those ions that 

 are actually involved in the precipitation, thus : 



Ag- 4- Cl' = AgCl. 



Reasoning parallel to the above may be applied when one of the 

 new products formed is a gas with slight solubility in water at ordi- 

 nary or higher temperatures, or a liquid which is volatile at elevated 

 temperature. In either case, the new product is removed as fast as 

 it is formed and the action runs to completion. In the liberation of 

 ammonia, the ionic equations are : 



2XH 4 C1 ^ 2C1' 4- 2NH 4 - 1 _ 



Ca(OH) 2 ; Ca- 4- 2(OHV / *~ 2 ^^*^H = 2H 2 O 4- 2NH 3 (gas) undissociated. 



It. 

 CaCl 2 soluble. 



Or, more simply, 



Ca- 4- 2(OH)' 4- 2NH 4 - 4- 2C1' == Ca' +2C1' 4- 2NH 4 OH. 



Ammonium hydroxide is only slightly ionized, and by heating is 

 easily broken up and driven out of solution as ammonia*gas. 



