34 



ANALYSIS FOR THE GROUl 



-KING 



3. Magnesium and the alkaline earths give a flocculent precipitate 

 which, in small quantities, does not interfere with the test. The sodium 

 precipitate adheres in part to the walls of the test-tube while the flocculent 

 precipitate can be removed easily by decanting. 



4. The sodium precipitate has a great tendency to form a supersatu- 

 rated solution. Rubbing the inside of the test tube with a stirring rod aids 

 the precipitation. Sodium should not be considered absent until the solution 

 has stood at least an hour or better overnight. Very often the compound 

 comes down in the form of a few crystals rather than as a precipitate. 



5. The flame test is not to be depended upon for the detection of sodium 

 because of its extreme delicacy. The amounts of sodium introduced from 

 the utensils, filter paper and dust give enough sodium to color the flame but 

 not sufficient to detect by the pyroantimonate test. 



Outline for the Analysis of Magnesium, Potassium and 

 Sodium. 



Filtrate from the Alkaline Earth Group Precipitation. 



(P.l) Evaporate. Add NH^OH and H3PO4. Filter. 



White granular ppte. 

 MgNH.PO^ 



(P.2) Extract with HjSO^. Add 

 alcohol. Filter. 



Ppte. 

 Alkaline 



Earth 



Sulphates 



Reject. 



Filtrate: 



(P.3) 



Add NH4OH and 



H3PO4 White 



gran. ppte. 



MgNH^PO^. 



.". Mg+ + 



Filtrate: (P.4) 

 Evaporate to dryness. Ignite. Dis 

 solve in HjO. Bubble in NO and 

 NO,. Boil. 



1/4 Solution. 



(P.5) Add 



Na.,Co(N02)6 



Yellow ppte. 



K,NaCo(NOj)r,. 



(P.6) 



Boil. Add 

 Naj Co(N0.)6 

 Yellow ppte. 

 K2NaCo(N02)6. 



.-. K+ 



3/4 Solution. 



(P.7) 



Add KjH.Sb.O; 



White cryst. ppte. 



Na2H2Sb,07. 



Na+ 



