24 Preparation of Substances 



When the two salts are dissolve! in water 

 all four ions, K+, Na+, CI", NOs", exist as 

 well as all possible combinations of these. 

 As water evaporates the least soluble com- 

 bination of ions, sodium chlorid, w^ill come out 

 of solution tirst, so that the reaction procedes 

 by metathesis, 



KCl + NaNOs = KNO3 + NaCl. 



It is to be noted in this reaction that as the 

 Na and CI ions form the least soluble sub- 

 stance so do the two ions remaining after 

 these unite, K+ and NOs", form the most 

 soluble combination. Either circumstance 

 would be sufficient to determin the direc- 

 tion of the reaction. 



The change in solubility of the potassium 

 nitrate in hot and cold solution is very great. 

 When hot potassium nitrate is many times 

 more soluble than sodium chlorid; at 33°, 

 their molar solubilities are equal and below 

 that temperature potassium nitrate is less 

 soluble, being about one-half that of sodium 

 chlorid at 10°. 



A graphic representation of the solubilities 

 of these salts will be of aid to the student. 

 Such figures are found in the following texts: 

 Kahlenberg, p. 435; Alexander Smith, p. 131; 

 Blanchard, Synthetic Inorganic Chemistry, 

 p. 26. 



