The Alkaline Earth Metals

advertisement
The Alkaline Earth Metals
Purpose:
To investigate some reactions of the Group 2A elements and gain some insight into the
properties of these alkaline earth metals.
Background:
The elements in Group 2A of the periodic table are called the alkaline earth metals. Like the
elements in Group 1A (the alkali metals), the elements in Group 2A are chemically active and
never found in nature in the elemental state. Like all members of a group, or family, the
elements in Group 2A share common characteristics.
The metallic character–the tendency to donate electrons during a chemical reaction–of the Group
2A elements increases as you down the group. The more metallic of these elements typically
react with water to form hydroxides and hydrogen gas. An example of such a reaction would be:
Ca(s) + 2H2O(l)

Ca(OH)2(s) + H2(g)
As metallic character increases (as you go down the group), the tendency for these elements to
form ions increases. Also, as you go down the group, the solubilities of the hydroxides formed
by the elements of this group increase. The more active the metal, the more basic its saturated
hydroxide solution.
The solubilities of alkaline earth compounds also show some interesting and useful tendencies.
For example, the sulfate compounds of alkaline earth metals show decreasing solubilities as you
go down the group. This characteristic is used as a means of separating and identifying metallic
ions of this group. Carbonates of all alkaline earth metals are quite insoluble.
In this experiment you will observe some of the characteristics of the alkaline earth metals
discussed here, and will write balanced chemical equations for the observed reactions.
Equipment:
Test tube clamp
Bunsen burner
Stirring rod
Test tube holder
Crucible tongs
Evaporating dish
Wash bottle and distilled water
safety goggles (worn at all times during the lab)
Wood splints
Test tubes, 18 x 150
Plastic reaction surface
Test tube rack
Ring stand
10-mL Graduated cylinder
Materials:
calcium turnings, Ca
magnesium ribbon, Mg
phenolphthalein solution
1 M ammonium oxalate, (NH4)2C2O4
1 M sodium carbonate, Na2CO3
1 M sulfuric acid, H2SO4
0.1 M magnesium nitrate, Mg(NO3)2
0.1 M strontium nitrate, Sr(NO3)2
0.1 M barium nitrate, Ba(NO3)2
0.1 M calcium nitrate, Ca(NO3)2
0.1 M Sodium chromate, Na2CrO4
Unknown salt solution
Procedure:
Part One Reaction of Calcium and Magnesium with Water
1. Pour about 5 mL of distilled water into a clean, dry medium test tube and clamp the test tube
on a ring stand. Add a piece of calcium metal to the water in the tube. Collect the gas generated
in an inverted medium test tube.
2. Test for the presence of hydrogen gas by inserting a burning wood splint into the upper part of
the inverted test tube.
3. Add a few drops of phenophthalein solution to the reactant tube. (A purple-red color
indicates the presence of OH- ions.) After making your observations discard the contents of the
test tube in the sink and clean the test tube with soap and water.
4. Repeat step 1 using a 10 cm piece of magnesium ribbon in place of the calcium. (Fold the
ribbon to completely submerge it in the water.) If no visible reaction occurs, heat the water to
boiling. Caution: The test tube should be clamped at a 45o angle and pointed away from
yourself and others.
5. Once the water is boiling turn off the gas, keep the test tube in the clamp, and allow the
reaction to proceed for several minutes.
6. Add a few drops of phenolphthalein to the reactant tube. Record your observations. Discard
the solution and take out the unreacted piece of magnesium. Uncoil the magnesium strip and
hold it at one end with the forceps. Place an evaporating dish under the magnesium and ignite
the strip in the Bunsen burner flame. Caution: Do not look directly into the light as the
magnesium. This could damage your eye. Turn off the burner.
Part Two Solubilities of Alkaline Earth Metals
7. Obtain a lab template and plastic wrap. Prepare the reaction surface for the experiment.
8. Add 2 drops of magnesium nitrate solution to the four areas on the reaction surface.
9. Add a few drops of 1 M sulfuric acid (this introduces the sulfate, SO42-, ion) to the sample of
magnesium nitrate. If a metal sulfate is insoluble in water a precipitate will be formed upon
addition of sulfuric acid. Record the solubility of each alkaline metal sulfate as either soluble
(S), or insoluble (I).
10. Add 1 M sodium carbonate to the second sample, 1 M ammonium oxalate to the third, and 1
M sodium chromate to the last sample.
11. Repeat steps 8 through 10 using calcium nitrate, strontium nitrate, and barium nitrate in
place of the magnesium nitrate. Record your results on the report sheet.
12. Dispose of the waste as directed in class.
Names_________________________________
_________________________________
________________________________
Date________________________
The Alkaline Earth Metals
Data and Observations
Part 1
Calcium and Water
Result of test for hydrogen gas:
Result of adding phenolphthalein:
Magnesium and Water
Result of adding phenolphthalein:
Observations during burning of magnesium ribbon:
Part 2
Solubilities of Salts of Group 2A Elements
Mg(NO3)2, Mg2+
Ca(NO3)2, Ca2+
Sr(NO3)2, Sr2+
Ba(NO3)2, Ba2+
Unknown
H2SO4
Na2CO3
(NH4)2C2O4
Na2CrO4
(SO42-)
(CO32-)
(C2O42-)
(CrO42-)
Unknown # _______
Identity of cation in unknown ________
Questions (Answer the following questions completely.)
1. List the alkaline earth metals tested in this experiment in order of increasing solubility.
2. Which is more reactive: magnesium or calcium?
3. Which group includes the more reactive metals: the alkali metals or the alkaline earth metals?
4. Write the chemical equation for the reaction of potassium and water.
5. Write the chemical equation for the reaction of magnesium and water.
4
Download
Related flashcards

Chemical properties

18 cards

Metallurgy

38 cards

Dyes

45 cards

Acids

25 cards

Analytical chemistry

34 cards

Create Flashcards