THE ANALYSIS OF THE GROUP V METALS

(Na, K & Mg)


PROCEDURE 1. Solution from the Group IV separation: Na+, K+ and Mg++. Add to this solution 1 drop of 4M ammonium oxalate (NH4)2C2O4 and 1 drop of 1M ammonium sulfate (NH4)2SO4. Separate and discard any precipitate that may form and use the solution for procedure (2).

PROCEDURE 2. Solution from (1): Na+, K+ & Mg++. To 2 drops of the solution from (1) or the Group V known or unknown add 1M CH3COOH until the solution is acid to litmus. Add 1 drop of this acidified solution to 5 drops of Sodium Reagent. Shake the mixture and set it aside for an hour. The formation of a yellow crystalline precipitate indicates the presence of sodium.

PROCEDURE 3. Use 10 drops of the solution from (1) or 10 drops of the Group V known or unknown: Na+, K+, Mg++. Add 4M aq. ammonia to the solution unit it is alkaline to litmus and then add 1 drop in excess. Now add 2 drops of 1M Na2HPO4 to the solution. The formation of a white crystalline precipitate, often slow in formation, confirms the presence of magnesium. Separate the mixture and save the solution for procedure (4). Dissolve the precipitate in a mixture of 2 drops of 1M acetic acid and 3 drops of water. Add 1 drop of Magnesium Reagent and an excess of 4M sodium hydroxide to the solution. The formation of a blue precipitate confirms the presence of magnesium.

PROCEDURE 4. Solution from (3): Na+, K+ & Mg++. Add 4 drops of conc. HNO3 to the solution held in a casserole, evaporate it to dryness, and then heat the dry residue for several minutes. After the casserole is cool, add 1 drop of 1M HCl and 5 drops of 4M acetic acid to the residue and boil the resultant solution. Now add 2 drops of this solution to 5 drops of a saturated solution of Na3Co(NO2)6. The formation of a yellow precipitate confirms the presence of potassium.

PROCEDURE 5. Original known or unknown solution for Group V or solution from procedure (1). Make flame tests on this solution and compare with known solutions of the ions in question. When testing for K+, observe the flame through a cobalt glass. Potassium gives a violet color to the flame. Sodium ions impart an intense yellow color to the flame. A trace of the sodium ion as a contaminant will give a yellow coloration to the flame, so do not rely entirely upon the flame test in reporting the presence of sodium.


Created by James R. Fromm (jfromm@3rd1000.com)