Name: ____________________________
Reactivity of Alkaline Earth Metals
Introduction:
The elements on Group 2A of the periodic table are called the alkaline earth metals. Why do they have
such a strange-sounding name? They were given the name because they were first isolated from compounds in
which they were combined with oxygen. These were called “earths” by early chemists. The alkaline part of the
name came from the fact that they formed basic, or alkaline, solutions in water. The group is composed of
beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra).
All alkaline earth metals have two valence electrons, which they tend to give up rather easily, making
them quite reactive. In fact, they are so reactive that they are never found uncombined in nature. In order for
these shinny white metals to remain in their un-reacted state, they must be protected from air and water.
Magnesium and calcium, for example, are obtained in their elemental state by a chemical process called
electrolysis, and then stored in airtight containers.
In this investigation, you will explore the reactivity of magnesium and calcium, two of the more
common alkaline earth metals. In order to test how the metals react, you will add water to the metals and
observe the reactions. If the metal does react with water, it will produce an alkaline solution. To see if the
solution is alkaline, we will use a chemical indicator called phenolphthalein. Phenolphthalein turns pink in the
presence of a base (an alkaline solution) but remains colorless if there is no base. If there is no reaction, the
solution will not turn pink with phenolphthalein. You will then compare the reactivity of these metals with that
of aluminum, which is a member of Group 3A (13).
To test how the metals react with oxygen, we will burn small pieces of magnesium and aluminum and
test the products with the phenolphthalein indicator.
Pre Lab Discussion:
1. What are some of the properties shared by alkaline earth metals?
2. How many valence electrons do the alkaline earth metals have in their elemental state?
3.
What are some of the hazards of working with metals that are as active as the alkaline earth metals? What
precautions should you follow?
4. If a piece of metal, such as calcium or magnesium, reacts with atmospheric oxygen, would you expect the
product to have a greater or lesser mass than the reacting metal? Why?
5. What does a pink color with phenolphthalein indicate?
6. How should you dispose of the products of the reaction of calcium and water?
Procedure:
Part A – Reaction of Metals with Water
1. Put on your goggles. Open the petri dish and put a small layer of water in the bottom using your distilled
water bottle.
2. Obtain a piece of calcium from your teacher and put it in the dry side of the petri dish. Write down your
observations of the un-reacted calcium.
3. Without touching the calcium, put the piece of calcium into the dish with water and immediately cover the
dish. CAUTION: the reaction products of calcium and water can cause skin irritation. Write down your
first observations. If any piece of metal is un-reacted, lift the cover at an angle away from you and gently
squirt the metal with a little more water. Replace the cover over the petri dish immediately. Repeat if
necessary until there is no further reaction. Write down your final observations of the calcium and the
reaction products.
4. When the reaction is completely finished, open the petri dish and place a drop of phenolphthalein on the
reaction products. Record the color change, if any, that occur over the next three minutes.
5. Using a squirt bottle, rinse out your petri dish into the container for calcium waste as directed by your
teacher. Make sure to completely rinse out all products from the first reaction.
6. Obtain a piece of magnesium ribbon from your teacher. Use a small piece of steel wool to clean the Mg
ribbon. Record the appearance of the clean Mg ribbon.
7. Place the Mg ribbon into one side of the petri dish. Add a small layer of water and observe the reaction, if
any.
8. Add a couple drops of phenolphthalein to the Mg and water and record any color changes that you observe.
9. Repeat Steps 6-8 with a small piece of aluminum in the other side of the petri dish.
10. Using the forceps, remove and dry the solid pieces of magnesium and aluminum for use in Part B.
11. Pour the solutions from the petri dishes down the drain. Wash all the petri dishes with water and dry them.
Part B – Reaction of Metals with Oxygen (Combustion Reaction)
1. Place a small amount of water into each of the sides of the petri dish.
2. Light the burner. CAUTION: The gases produced in Part A are explosive. Before lighting the burner,
make sure everyone is finished with Part A.
3. Hold the magnesium ribbon over the flame with the crucible tongs. As soon as it lights, hold the burning
magnesium over the wire gauze square. CAUTION: Do not look directly at the burning magnesium, as it
can damage your eyes. Keep loose hair and clothing away from the fire. When the fire is out, examine the
products of the burn and record your observations in the Data Table.
4. Place the product of the burn into the water in one side of the petri dish and add a drop of phenolphthalein
solutions. Record your observations.
5. Repeat Steps 3 and 4 with the aluminum foil. Record your observations. If attempts to burn the aluminum
are unsuccessful, drop a microspatula of aluminum oxide into the water of the petri dish. Place a drop of
phenolphthalein solution on the aluminum oxide and record your observations.
6. Wash the contents of the two petri dishes down the drain with excess water and dry the dishes. Clean up
your work area and wash your hands before leaving the laboratory.
Observations:
Part A: Data Table 1
Step
Description
2
unreacted Ca
3
Ca + water (initial)
3
Ca + water reaction products (final)
4
Ca + water + phenolphthalein
6
unreacted Mg
6
Mg after cleaning with steel wool.
7
Mg + water
8
Mg + water + phenolphthalein
9 (6)
unreacted Al
9 (7)
Al + water
9 (8)
Al + water + phenolphthalein
Observations
Part B: Data Table 2
Step
Description
3
Mg burning
4
Burned Mg + phenolphthalein
5 (3)
Al burning
5 (4)
burned Al (or Al2O3) + phenolphthalein
Observations
Conclusion:
1. Phenolphthalein turns pink in basic, or alkaline, solutions. Did the reactions of the alkaline earth metals
with water produce alkaline solutions?
2. What evidence do you have that there was a pattern of reactivity in the alkaline earth metals?
3. List Mg, Ca and Al in order of reactivity.