Lab 10
Denise Jenke
Chemistry 4/5
10/3/98
The Alkaline Earths—A Family in the Periodic Table
Introduction:
The periodic table arranges elements in order of increasing atomic numbers so that similar properties
recur in a set pattern. In this way elements in the same family have physical and chemical properties
which gradually change as one goes from the top of the column to the bottom. In this experiment we
examined one periodic property: reaction of the alkaline earth metals to form compounds of differing
solubility. As one goes down the family we should see a pattern or trend in the solubility of the
compounds formed.
Purpose:
The objective of this experiment was to confirm the order of the alkaline earth metals in the periodic table
by comparing the way they react with different compounds. In this case, the nitrate salts of barium,
calcium, magnesium and strontium were mixed with various carbonates, oxalates, sulfates and chromate
and the reactions were observed. If a precipitate was formed the resulting compounds was judged
insoluble, if no precipitate formed it was soluble. Our hypothesis is that by comparing the solubility of
these compounds we should be able to confirm the order of the alkaline earth metals; calcium,
magnesium, strontium, and barium, in order of decreasing solubility as they appear in the periodic table.
Procedure:
1. Into each of four test tubes add 1 ml of 1-M sulfuric acid.
2. Add 1 ml of 0.1 M of these compounds: magnesium nitrate, calcium nitrate, strontium nitrate, and
barium nitrate, one to each test tube.
3. Mix, observe the reaction and record observations.
4. Rinse out the test tubes.
5. Repeat Steps 1-4 three times substituting first 1 M sodium carbonate, then 0.25 M ammonium
oxalate and finally 1 M potassium chromate (plus 1 ml of 1 M acetic acid) for the 1 M sulfuric acid
in step 1.
6. Compare results and determine the order of the metals.
Observations:
Key: P = precipitate formed S = no precipitate formed
Compounds
1M sulfuric acid
mixed
1 M sodium
0.25 M
1 M potassium
carbonate
ammonium
chromate + 1 M
oxalate
acetic acid
Barium nitrate
P/white
P/white
P/white
P/white
Calcium nitrate
S
P/white
P/white
S
Magnesium
S
P/white
S
S
P/white solid
P/white
P/white
S
nitrate
Strontium nitrate
Data: Not applicable in this lab (in a "real" report this section would be eliminated)
Analysis:
Compounds mixed
Number of insoluble compounds formed
Barium nitrate
4
Strontium nitrate
3
Calcium nitrate
2
Magnesium nitrate
1
Insoluble Products of Chemical Reactions
Conclusion:
On the basis of the trends observed we list the alkaline earth metals in the way they should appear in the
periodic table: Mg, Ca, Sr, Ba, in order of decreasing solubility. We arranged them in this order based on
the following observations:
1. Barium compounds were least soluble; they formed precipitates when added to all four solutions.
2. Magnesium formed compounds that were the most soluble: they were insoluble only in the case
where magnesium nitrate was added to sodium carbonate.
3. Calcium formed two soluble compounds (with sulfuric acid and potassium oxalate) and strontium
formed only one soluble compound (with potassium chromate) so calcium compounds were
determined to be more soluble than strontium compounds.
The order of Mg, Ca, Sr, Ba is consistent with the properties of the cations in all of the precipitating
reagents.
In conclusion, we supported our hypothesis in this experiment, by comparing the solubility of the alkaline
earth compounds we could confirm the order of the alkaline earth metals; Mg, Ca, Sr, and Ba, in the
periodic table.
Possible sources of error in this experiment: contamination of solutions prior to lab or during lab by using
dirty test tubes. Since we supported our hypothesis and obtained the results we expected neither of these
sources lead to any significant error in this procedure.