Solubility of Alkaline Earth Metal Compounds
BACKGROUND:
NAME
The alkaline earth metals - beryllium, magnesium, calcium, strontium, barium, and radium - are a reactive
group of metals. Because they combine easily with many other elements, the alkaline earth elements are not
found on Earth in the form of their free metals. The alkaline earth metals react with water, acids and bases,
and many nonmetals, including oxygen, sulfur, and the halogens.
Similarities and differences among the elements on the periodic table give rise to periodic trends, both across
rows and within columns of the table. Recognizing periodic trends and chemical properties of the elements
is important to understanding the full value of the periodic table. In this experiment, you will observe a
series of reactions (chemical reactivity and solubility) for several alkaline earth metals. From this data, you
will be able to determine the periodic trend for the metals within a group.
OBJECTIVES:
 Identify periodic trends in the solubility of the alkaline earth metals.
 Determine the trends within a group.
PROCEDURE:
Equipment:
1 12 well plate
Drop bottles of
Na2CO3
Na2SO4
K2CrO4
Pipettes of metal chlorides
MgCl2
CaCl2
SrCl2
BaCl2
1. You will use your reaction well plate or dish for part B. In this part, you will mix 4 known metal
chloride solutions (MgCl2, CaCl2, SrCl2, BaCl2) with 3 testing solutions (Na2CO3, Na2SO4, and K2CrO4).
Each of the four known metal solutions contains a member of the alkaline earth family (Mg2+, Ca2+, Sr2+,
Ba2+).
2. Set up a grid of the metal chlorides, such that there is a row with 3 wells for each metal chloride. Place 34 drops of a single metal chloride in each of 3 wells in the row. Continue with the other 3 metal chlorides,
until there are 4 rows with 3 wells of each metal chloride.
3. Add 3-4 drops of Na2CO3 to one column of the well plate, so that 1 well of each of the metals reacts with
Na2CO3. Repeat with Na2SO4 and K2CrO4. Carefully observe each well, and note whether a precipitate
(solid or cloudy solution) forms, the amount of precipitate produced and the speed with which it forms.
Record your observations in the data table.
.
Data Table:
Na2CO3
Na2SO4
K2CrO4
Alkaline Earth Ion
Mg++
Ca++
Sr++
Ba++
ANALYSIS QUESTIONS 1. Write a balanced equation for each of the mixtures that formed a precipitate
2. Underline the product that is the precipitate. How do you know which of the two salts will precipitate?
3. Which alkaline earth formed the most precipitates? The fewest?
4. What is the valence electron configuration for each of these metals? How does the charge on all of these
ions relate to the electrons in the valence (outermost) shell?
5. Write a general statement that describes the periodic trend in the solubility of alkaline earth metal
compounds.
6. Based on your answer to problem 6, what would you predict would happen if you preformed the same
experiment with BeCl2? RaCl2?
7. How does the solubility of these alkaline earths compare with the solubility of Na+?