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.
3.
4.
How many valence electrons do the alkaline earth metals have in their elemental state?
What are some of the hazards of working with metals that are as active as the alkaline earth metals?
What precautions should you follow?
Do these metals like to gain or lose electrons?
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
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.
1.
1.
2.
3.
4.
5.
6.
Part B – Reaction of Metals with Oxygen (Combustion Reaction)
Place a small amount of water into each of the sides of the petri dish.
Light the burner. CAUTION: The gases produced in Part A are explosive. Before lighting the burner,
make sure everyone is finished with Part A.
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.
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.
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.
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.
Conclusion Part 2
Are magnesium and calcium more reactive with oxygen in the air than aluminum? What evidence
from the lab supports your answer?
Using the periodic table, do you think strontium would be more or less reactive than calcium?
Which of the metals in the lab do you think was used as the first photography flash?
Explain why aluminum was chosen as the comparison point for this lab. It may be helpful to consider
other choices that could have made as well as why it would be useful to have a metal with reactions
like aluminum.
Aluminum is a metal commonly used in making electrical and structural materials. Based on your
results, why does this make sense?
Part 3: Demonstrations—We are now going to look at 2 metals from a different group on the periodic table.
We are going to look at Sodium and Potassium.
What group are these 2 metals in on the periodic table?
How many valence electrons do they have?
Are these metals more or less reactive than the group 2 metals? Why do you think this is the case?
Which is more reactive between Sodium and Potassium? Why do you think this is the case?
Do these metals turn the water alkaline? What is causes water to become basic?
Part 4 Another property of these properties of Group IIA is the ability to form a precipitate, or solid substance,
as a result of a chemical reaction. The precipitate cannot dissolve in water and eventually settles to the bottom
of the container. In this investigation, you will compare the abilities of the alkaline earth elements to form
precipitates as a result of a chemical reaction.
Materials (per group)
Safety goggles
Spot plate
Sheet of notebook paper
Dropper bottles of:
magnesium nitrate
calcium nitrate
strontium nitrate
barium nitrate
potassium carbonate
potassium sulfate
potassium chromate
Mg(N03)2
Ca(N03)2
Sr(N03)2
Ba(N03)2
K2C03
K2S04
K2CrO4
Procedure
1. Place the spot plate in the center of a sheet of notebook paper so that there are 4 spots running down
and 3 spots running across. See Figure 1.
2. Along the side of the notebook paper next to each of the four spots, write the names of the four alkaline
earth elements that are present in each nitrate compound listed in the materials you are using. Write
them in the same order in which they are listed. See Figure 1.
Figure 1.
3. Along the top of the notebook paper next to each of the three spots, write the names of the three
substances that are combined with potassium in the materials you are using. See Figure 1.
4. Put on your safety goggles.
 Place 3 drops of potassium carbonate in each of the four spots under the word “carbonate.”
 Place 3 drops of potassium sulfate in each of the four spots under the word “sulfate.”
 Place potassium chromate in each of the four spots under the word “chromate.”
*Be very careful not to mix the liquid from one spot with the liquid from another.
5. Take the dropper bottle of magnesium nitrate and place 3 drops in each of the three spots in the row
labeled “magnesium.” Observe each spot carefully and record the result in the Data Table.
*Remember you are looking for a precipitate to form.
6. Repeat this procedure using the dropper bottles containing
 calcium nitrate in the row labeled “calcium”
 strontium nitrate in the row labeled “strontium”
 barium nitrate in the row labeled “ barium”
*Be very careful not to mix the liquid from one spot with the liquid from another.
6. After recording your results, wash your spot plate thoroughly with soapy water and a brush.
Pre-Lab:
Define the term precipitate: ______________________________________________________________
Observations
DATA TABLE
Alkaline earth metal
Magnesium
Calcium
Strontium
Barium
Carbonate
Sulfate
Chromate
Conclusions
1.Was there any evidence of a chemical reaction occurring in any of the spots? ______________________
Explain your answer.
__________________________________________________________________________________
__________________________________________________________________________________
2. Which alkaline earth element formed the smallest number of precipitates? _______________________
3. Which alkaline earth element formed the greatest number of precipitates? _______________________
4. What is the relationship between the number of precipitates formed and the location of the alkaline
earth element on the periodic table?
_________________________________________________________________________________
_____________________________________________________________________________________
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5. If the ability of an alkaline earth element to form a precipitate is an indication of its ability to
chemically react with other substances, which is the most reactive element?
_______________________
The least reactive?____________________________
6. List the alkaline earth metals (used in this lab) in order of their chemical reactivity, starting with the
most reactive. 1.(most) _______________________
2. ___________________________
3. ___________________________
4. __________________________