THE ANALYSIS OF THE GROUP IV METALS

(Ba, Sr & Ca)


PROCEDURE 1. Precipitation of the Group IV Ions. Ba++, Sr++ and Ca++. Evaporate the solution (10 drops of a Group IV known or unknown or the solution from the Group III separation) to dryness and ignite in a casserole to expel ammonium salts. Dissolve the residue in a mixture of 1 drop of 12M HCl and 12 drops of H2O Make the solution alkaline by adding 4M aq. ammonia. Add just one drop of aq. ammonia in excess. Add 2 drops of 1M ammonium carbonate (NH4)2CO3, or more if necessary, to effect complete precipitation, and warm the mixture in a hot water bath. Allow the mixture to cool; separate the precipitate and reserve the solution for the Group V Analysis.

PROCEDURE 2. Precipitation from (1): BaCO3, SrCO3 and CaCO3. Dissolve the precipitate in a mixture of 2 drops of 4M acetic acid (CH3COOH) and 4 drops of 1M ammonium acetate (NH4C2H3O2). Add 1 drop of 1M potassium chromate (K2CrO4) to the solution. The formation of a yellow precipitate indicates the presence of barium. Separate the mixture and reserve the solution for procedure (3). Dissolve the precipitate barium chromate (BaCrO4) in 2 drops of 12M HCl. Make a flame test on the solution for the barium ion. The barium ion imparts a greenish-yellow color to the Bunsen flame. Add 1 drop of 4M sulfuric acid (H2SO4) to the remainder of the solution. A white precipitate (BaSO4) confirms the presence of barium.

PROCEDURE 3. Solution from (2): Sr++ and Ca++. Add 4M aq. ammonia to the solution until the color changes from orange to yellow. Now add enough ethanol (CH3CH2OH) equal to the volume of the solution. The formation of a fine yellow precipitate indicates strontium chromate (SrCrO4). Separate the mixture and reserve the solution for procedure (4). Dissolve the precipitate in 2 drops of 12M HCl and make a flame test on the solution for the strontium ion. A crimson color imparted to the flame is characteristic of the strontium ion.

PROCEDURE 4. Solution from (3): Ca++. Heat the solution to boiling and add 2 drops of 0.4M ammonium oxalate ((NH4)2C2O4). The formation of a white precipitate confirms the presence of calcium. Dissolve the precipitate in 12M HCl and make a flame test on the solution. Calcium ions impart a brick red color to the flame.


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