EXPERIMENT QA2
Alkaline Earth Metal Ion
Qualitative Analysis
The chemistry of the Alkaline Earth Metals (Group II) Ions are very similar, however they
do have slightly different solubilities with the appropriate Anion Reagent. In this
experiment you will examine the anions capable of separating the Metal ions and you will
devise a separation scheme that will allow you to successfully identify the contents of an
unknown containing a mixture of the metal ions.
SOLUTIONS
Ba(NO3)2
Sr(NO3)2
Ca(NO3)2
Mg(NO3)2
REAGENTS
K2CrO4
(NH4)2 C2O4
(NH4)2 SO4
NH3
--->
--->
--->
--->
Cation Used
Ba2+
Sr2+
Ca2+
Mg2+
--->
--->
--->
--->
Anions Used
CrO42Chromate
C2O42Oxalate
2SO4
Sulfate
OH1Hydroxide
Barium
Strontium
Calcium
Magnesium
PROCEDURE:
Reagent\Soln
Ba2+
Sr2+
Ca2+
Mg2+
2CrO4
C2O42SO42OH11. In a 96 well reaction plate place a couple drops of each SOLUTION. Add a couple
drops of each REAGENT to each SOLUTION and make observations. Your data table
should look as above:
2. Using the data from above, devise a SEPARATION SCHEME that will allow you to
separate a mixture of the alkaline earth metal ions from each other. Mr. Godfrey will
explain how in class. A skeletal framework for your separation is provided on the back.
Have your scheme OK’d by the teacher before you go any further!!
3. Obtain an unknown from the teacher. Record its code letter in your data book. Add
about 1 cm of the unknown to a small test tube and add your first reagent. You MUST
follow the separation scheme you developed!!
a. Add reagents drop wise; If no precipitate is observed follow your scheme to the
next reagent.
b. If, after you add a few drops of a reagent you get a precipitate you must remove
all of that precipitate before you can go on. To do this, add several drops of reagent until
you no longer see precipitate forming. Centrifuge. To the centrifuged test tube and
solution, add another drop of reagent. If no more precipitate forms, drive on. If more
precipitate forms, add enough reagent to get it all then re-centrifuge.
Ba+2, Sr2+, Ca2+, Mg2+
Reagent:
Soln
PPT
3 Cations
PPT
Reagent:
2 Cations
PPT
Reagent:
1 Cation
PPT
Reagent:
PROCESSING THE DATA:
In your abstract, explain the ions you have and don’t have. Your lab grade will be based
upon
a. A well written abstract
b. The correct identification of all unknown ions.
c. Well documented data.
d. A completed separation scheme showing the correct formulae of all reagents
and precipitates.
ADDITIONAL, OPTIONAL PROCEDURE: FLAME Test
1. Add 1 mL of the appropriate cation solution (except magnesium) solution to 1 ml of the
carbonate reagent in a small test tube. CENTRIFUGE, decant and discard the liquid.
Add 6 M HCl to the carbonate precipitate to dissolve it. Just a drop or two will do.
2. Get a flame test loop. Dip the loop into the solution from above then into a Bunsen
burner flame and note the color.
3. Repeat steps 1 & 2 using a fresh sample of the unknown.