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Reactivity of Alkaline Earth Metal


									Reactivity of Alkaline Earth Metal                                 Name__________________________

35 Points                                                          Period________Date______________

Background: The elements in Group IIA (2) 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 shiny white metals to remain in their unreacted 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 to decide if reactivity increases or decreases going down a group in the
periodic table. Then you will compare their reactivity with aluminum which is in Group IIIA (13) across
to the right of magnesium to decide if reactivity increases or decreases going across a period on the
periodic table.

Hypothesis: Among the metals on the periodic table reactivity ____________________ across a period

              and _____________________ down a group.

Prelab Questions:

   1. What common substances do alkaline earth metals react quickly with? ______________________

   2. How many valence electrons do the alkaline earth metals have in their elemental state? _________

   3. What are some hazards of working with very reactive 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 the phenolphthalein solution indicate? _________________________

   6. How should you dispose of the calcium & water reaction products? _________________________

Materials:    goggles        apron                  3 covered plastic petri dishes       marking pencil
              forceps        spoon                  phenolphthalein dropper bottle       wash bottle
              Al foil        Ca metal               Mg ribbon                            steel wool
              striker        Bunsen burner          aluminum oxide (Al2O3)               crucible tongs

        Wear your goggles and lab apron at all times during the investigation. Avoid touching calcium
metal or calcium oxide (the reaction product) directly. Any skin or clothing that comes in direct contact
with calcium metal or its reaction products should be washed with large quantities of water. If the
exposed skin feels slippery, continue to rinse it with water.
        Make sure no open flames are present in the laboratory when reacting calcium with water because
the gas that is produced can be explosive. Carry out this reaction in a covered petri dish.
        Make sure that everyone is finished with Part A before doing Part B. Tie back hair and loose
clothing to avoid any fire hazard. When you burn magnesium, avoid looking directly at the flame, which
is hot and burns very bright. Note the caution directions within the procedure for more specifics.


Part A

   1. Put on your goggles and lab apron. Obtain 3 sets of petri dishes from the lab bench and mark the
      covers with Ca, Mg and Al using your grease pencil.
   2. Remove the covers and rest them open side up on the lab bench. Obtain a 4 cm strip of
      magnesium ribbon, a small piece of aluminum foil and a few small pieces of calcium and place in
      the separate petri dishes. Be sure to use a spoon for the calcium; do not touch the calcium
      directly. Record the appearance of each meal in Data Table 1 before starting the experiment.
   3. Using the wash bottle with distilled water, squirt a small amount of water into the Calcium labeled
      petri dish and place the calcium metal into the water. Immediately put the cover on the dish and
      observe the reaction for several minutes. Record your observations in Data Table 1. Caution: the
      reaction products of calcium and water and cause skin irritation, observe through the cover.
   4. If any piece of metal is left unreacted, lift the cover at angle away from you and gently squirt the
      metal with more distilled water. Place the cover over the petri dish again immediately. Repeat if
      necessary until there is no further reaction.
   5. Open the petri dish and place a drop of phenolphthalein on the reaction products. Record the color
      change, if any, which occurs.
   6. Follow steps #3-5 with the magnesium strip and then with the aluminum foil. You need not place
      the covers on the dishes. Record your results in Data Table 1.
   7. Using the wash bottle, rinse the products of the calcium metal reaction into the trash. Put the
      metals from the other solutions in the trash and rinse the petri dishes with water, dry them and
      clean up your station.

Part B

   8. Using only the Al and Mg marked petri dishes, obtain another piece of aluminum and magnesium.
   9. Light the lab 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 Data Table 2.
   10. Place the products of the burn into the water in the petri dish labeled Mg and add a drop of
       phenolphthalein solution. Record your observations.
   11. Repeat steps 9 and 10 with the aluminum foil. Record your observations. If attempts to burn
       aluminum are unsuccessful, obtain the aluminum oxide powder from the supply table and add a
       very small scoop to the water in the petri dish labeled Al. Place a drop of phenolphthalein solution
       on the aluminum oxide and record your observations.
   12. Wash the contents of the two petri dishes down the drain with excess water and dry the dishes.
       Clean up and wash your hands before leaving the laboratory.


                      Data Table 1 Observations of Alkaline Earth Metals
 Step            Reaction Description                                Observations
   2         Appearance of unreacted Ca
   2         Appearance of unreacted Mg
   2         Appearance of unreacted Al
   3         Ca + water
   5         Ca + water + phenolphthalein
   6         Mg + water
   6         Mg + water + phenolphthalein
   6         Al + water
   6         Al + water + phenolphthalein

                      Data Table 2 Comparisons of Alkaline Earth Metals
 Step            Reaction Description                                Observations
   9         Mg burning
   10        Burned Mg + phenolphthalein
   11        Al burning
   11        Al2O3 + phenolphthalein

Conclusions: Use the results of this experiment to answer
                                                                                  Group Number
the following question. Among the metals on the
                                                                                     2       13
periodic table reactivity ____________________ across a period
                                                                              3     Mg       Al

and _____________________ down a group.
                                                                              4     Ca
(2 points)
                                                                              5     Sr
Questions: (22 points)

1. Unreacted calcium and magnesium metal are shiny when they are pure. If the metals you worked with
   were not shiny, explain why.


2. Would you describe the reaction of calcium in water as being exothermic (energy releasing) or

  endothermic (energy absorbing)? ________________ Why? _________________________________

3. Phenolphthalein appears pink in a basic or alkaline solution. Did calcium react with water to produce

  an alkaline solution? ________How do you know? __________________________________________

4. Did magnesium react with water to produce an alkaline solution? ________How do you know?


5. Groups of metals change in reactivity from the top to the bottom of the periodic table. Alkaline Earth

  metals get more / less reactive as you go down the group. (circle one)

6. Did aluminum react with water? _______ How do you know? _________________________________

7. Are magnesium and calcium more reactive with oxygen in the air than aluminum? _________ Explain.


8. When you added phenolphthalein to the solutions of the magnesium and aluminum powder it

   turned pink / stayed clear. This means the solutions were acidic / basic. Name another term for

   basic: _________________________.

9. Look at strontium (Sr) on the periodic table. Would you expect it to be more or less reactive than

  calcium? ___________ Explain. ________________________________________________________

10. Which of the metals in this lab could you use for a camera flash? _________ Why? _______________


11. Would you expect to find calcium metal used in electrical wiring or structural materials? ___________

   Why or why not? ____________________________________________________________________

12. Aluminum is a metal commonly used in making electrical wiring, and structural materials.

   Why is aluminum used and not magnesium or calcium? ____________________________________

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