Reactivity of Selected Families of Metals

Reactivity of Selected Families of Metals

Prelab

In this investigation you will determine the periodic trend for reactivity for a selection of different metals: Calcium, Magnesium, Aluminum and Sodium. Before doing so, it would be helpful to research (from verifiable sources, textbook, reliable website, etc.) some information regarding these metals and the families they belong to. Record information regarding your information sources in order to cite where you found your information (MLA format). Research should determine some unique characteristics of each group of chemicals.

Prelab Questions

1.  What are some of the properties shared by alkali metals (Group 1/IA)? What are some properties shared by alkaline earth metals (Group 2/IIA)? What are some properties shared by metals in general?

2.  How many valence electrons do the alkaline earth metals have in their elemental state? How many valence electrons do alkali metals like sodium, and Group 13 elements like aluminum have? What is the significance of those valence electrons?

3.  What are some of the hazards of working with metals that are as active as the alkali metals and 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 that the reacting metal? Why? Predict a chemical equation that would describe this reaction (hint: this is a synthesis reaction, maybe check page 284 for some information about what this equation/reaction might look like).

5.  What does a pink color with phenolphthalein solution indicate (hint: phenolphthalein is an acid/base indicator, maybe look at Chapter 19 for information)?

6.  How should you dispose of the products of the reaction of calcium and water? Why is it necessary to deal with these products more carefully than just putting them down the drain?

I.  Purpose

How do the activities of the alkaline earth metals (Group 2/IIA) magnesium and calcium compare to each other and to both aluminum (Group 13/IIIA) and sodium (an alkali metal, Group 1/IA)? Hypothesis: Will metals near the top Group 2 be more or less reactive than metals near the bottom of group 2?

II.  Materials

Chemical splash goggles Phenolphthalein indicator Watch glass

Laboratory apron Steel wool Micropipette

Wax marking pencil Wash bottle with distilled water Forceps

Aluminum foil (Al) Bunsen burner Striker or matches

Magnesium ribbon (Mg) Crucible tongs 3 petri dishes

Calcium metal turnings (Ca) Wire gauze square

Safety

Wear your goggles at all times during the investigation. Avoid touching calcium metal or calcium oxide directly. Any skin or clothing that comes into 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 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 the magnesium, avoid looking directed at the flame, which is hot and very bright.

III.  Procedure

Part 1 – Single Replacement Reactions

1.  Put on your goggles. Label three petri dishes and their covers Mg, Ca, and Al, using the marking pencil.

2.  Remove the covers of the petri dishes and rest them open side up on your lab table. Use the forceps to place the following metal samples in the labeled petri dish covers: a 2cm piece Mg ribbon, a small piece of Ca turning, and a piece of aluminum foil about the size of the Mg ribbon. CAUTION: Do not touch the calcium turning with your hands, it is corrosive.

3.  Place three micropipettes of distilled water into each of the petri dish bottoms (metal samples are on the lids).

4.  Obtain a bit of steel wool and use it to clean/polish the strip of Mg ribbon. Record the starting appearance of all three metals.

5.  With forceps, move the piece of calcium turning from the petri dish cover and place it into the petri dish. Place the cover over the petri dish immediately. CAUTION: The reaction products of calcium and water can cause a chemical burn. Observe the reaction through the plastic cover. Record your observations now, and after one minute. If any piece of metal is unreacted, lift the cover at an angle away from you and gently squirt the metal with one more pipette full of water. Place the cover over the petri dish immediately. Repeat if necessary until there is no further reaction.

6.  Move the pieces of magnesium and aluminum, placing those metals in the prepared petri dishes of water. You need not place the cover over these dishes. Watch closely for any sign of reaction. Record your observation in Data Table 1.

7.  Carefully open the Ca dish. Place a drop of phenolphthalein on each piece of metal in the three dishes. Record any color changes or additional sign of reaction that occur over the next three minutes.

8.  Using the forceps, remove and dry the solid pieces of magnesium and aluminum for use in Part B.

9.  Using the wash bottle, rinse the products of calcium metal reaction into the container your teacher has provided for calcium waste. Pour the solution from the other petri dishes down the drain. Wash all the petri dishes with water and dry them.

10.  If you do not go directly on to Part B, clean up your work area and wash your hands before leaving laboratory.

Part 2 – Synthesis Reactions

11.  Make sure your safety goggles are on.

12.  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.

13.  Place the product of the burned magnesium on a watch glass and add several drops of water. Add a drop of phenolphthalein solution. Record your observations.

14.  Repeat steps 12 and 13 with the aluminum foil. Record your observations.

15.  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.

IV.  Data

Data Table 1 Observations of metal reactions with water

Step / Observations
Unreacted Ca
Unreacted Mg
Unreacted Al
Unreacted Na
Ca during reaction with water
Ca at the end
Mg during reaction with water
Mg at the end
Al during reaction with water
Al at the end

Data Table 2 Comparisons of Alkaline Earth Metals

Reaction / Observations
Mg burning
burned Mg ( or MgO) + phenolphthalein
Al burning
burned Al (or Al2O3) + phenolphthalein

V.  Calculations: None for this lab

VI.  Questions

1.  Elemental (unreacted) calcium and magnesium metal are shiny when they are pure. If the metals you worked with were not shiny, explain why this was so. (generate conjecture)

2.  Would you describe the reaction of calcium in water as being exothermic (energy releasing) or endothermic (energy absorbing)? Use your observations as evidence to support your answer. (making observations, explain phenomena)

3.  Phenolphthalein appears pink in basic, or alkaline, solution. Did the reactions of the alkaline earth metals with water produce alkaline solutions? Explain your answer. (make and justify conjecture)

4.  Did magnesium metal react with water to form a gas and an alkaline solution? Explain your answer in light of your observations. (making observations, analyze multiple sources of evidence)

5.  Groups of metals change in reactivity from the top to the bottom of the periodic table. What evidence do you have that there was a pattern of reactivity in the alkaline earth metals? What is the underlying reason for this pattern? (specify and explain relationships)

6.  Was there any evidence that aluminum reacted with water? (interpreting data)

7.  Are magnesium and calcium more reactive with oxygen in the air than is aluminum? Support your answer. (drawing conclusions from data)

8.  What can you conclude from the color of the solutions made from magnesium and aluminum oxides (Part 2) when phenolphthalein was added? (generating conjectures)

9.  Look at strontium (Sr) in the periodic table. Would you expect it to be more or less reactive than calcium? Explain. (make and justify conjectures)

10.  If you were designing a construction project and you needed to choose between aluminum and calcium for electrical wiring (both metals conduct electricity) which would be the better choice, and why? (apply understanding in a novel way)

11.  Using graph paper obtained from your teacher, construct two graphs, one comparing atomic number (independent variable) to atomic radius (dependent variable) and a second comparing atomic number (independent variable) to ionization energy (dependent variable) for the four metals tested. For each graph, make a conclusion based on the data you have gathered. (gathering, analyzing and evaluating information)

Metal / Atomic Number / Atomic Radium (pm) / Ionization Energy (kJ/mol)
Sodium / 11 / 190 / 495.8
Magnesium / 12 / 145 / 1450.7
Aluminum / 13 / 118 / 2744.8
Calcium / 20 / 194 / 1145.4

VII.  Discussion of Error Discuss any errors from this experiment and describe how they can be corrected.

VIII.  Conclusion

Using your own words write a conclusion. The conclusion has the following basic format and should be 2 to 3 paragraphs long:

a.  Claim: Restate your Hypothesis.

b.  Evidence: Cite data from the experiment.

c.  Reasoning: How do your results explain the scientific principle explored in this lab? This is a research section. Use your text as one reference and you will need one additional reference beyond the text and the notes.

d.  Connections to the Real World: Explain how your results are related to something in the real world.

e.  Further Experiment: Give an idea for an experiment that tests this concept further. You may not describe the same experiment with different materials.