Name: ______________________________________________ Date: _____________ Hr: _______
Lab: Comparing Reactivity Within a Group and Across a Period
Objective: This lab will consist of three sections, one of which uses demonstrations and a video. In part 1 and part 2, you will be
gathering data to compare chemical properties of Group 2 metals (Mg and Ca) and Period 2 metals (Mg and Al) when exposed to air,
water, and heat. In part 3, you will observe the behavior of alkali metals when exposed to air and water.
Pre-Lab Questions:
1.
Write the electron configuration, list number valence electrons, and draw the electron dot diagram for Sodium, Potassium,
Magnesium, Calcium, and Aluminum.
2. Rank Na, K, Mg, Ca, and Al in order of decreasing atomic radius.
3. The chemical behavior of these metallic atoms is driven by desire to achieve a stable electron configuration. What will each of
these metals do with their electrons in order to reach a stable electron configuration?
4. What type of evidence of reaction should be present if the metals react with oxygen? With water?
Safety: Wear goggles and aprons at all times. Each of the metals (Ca, Mg, and Al) has the potential to react body tissue due to high
water content. A small amount of heat and flammable gas will be produced in parts 2 and 3—follow directions in order to prevent
exposure. DO NOT BEGIN PART 2 UNTIL EVERY GROUP IS DONE WITH PART 1. Part 1 involves the use of lab burners—secure
hair and remove all flammable sources (part 2 products and phenolphthalein). Do not look directly at the magnesium when it is being
burned.
Materials: 3 petri dishes (top and bottom), labeling paper, wash bottle, lab burner, striker, forceps, watch glass, magnesium, calcium,
aluminum, sand paper
Procedure:
Part 1: Observing Effects of Exposure of Al and Mg (period 3 metals) to Heat and Oxygen
1.
2.
3.
4.
5.
6.
7.
8.
9.
Dry each petri dish top and bottom.
Label three different pieces of marking paper with Mg, Al, and Ca. Place the paper under the bottom of the petri dish
Obtain samples of each metal from instructor and place in the LIDS of the open petri dishes.
Metals tend to form “oxides” when exposed to oxygen. You are familiar iron oxide, or rust. Metals tend to be lusterous, but
areas exposed to oxygen will form a dull coating. Examine each sample to determine if the metal reacted with oxygen.
In order to determine if the metals will react with oxygen, heat will be used to potentially speed up the process.
Beginning with the aluminum, use tongs and the lab burner to react the aluminum with oxygen in the air. A demonstration will
be done to clarify this process. Collect the ashes of the aluminum in a watch glass. Observe the ash for signs of reaction with
oxygen. Add enough water to cover the ash, and one drop of phenolphthalein. Record observations.
Repeat with the magnesium strip. Do not look directly at the magnesium when it is being burned.
Do NOT burn the calcium.
Rate the three samples based on reactivity with oxygen.
Name: ______________________________________________ Date: _____________ Hr: _______
PART 2: Observing Effects of Exposure of Al, Mg, and Ca to Oxygen and Water
10. Using the wash bottle, add enough water to the BOTTOM of the petri dish to fill half-way. Add 1 drop of phenolphthalein
(should not turn pink at this point). Since the metal samples in the petri dish top (not the bottom), the samples should not yet
be exposed to water.
11. Beginning with the Aluminum, add the Al sample to the water by flipping the top of the petri dish onto its bottom. These metals
will form bases IF they react with the water. If a base is formed, the phenolphthalein will turn a shade of pink. This reaction (if
it occurs) will also produce hydrogen gas, and would be an exothermic reaction. Observe for three minutes over the white
paper, then record observations in data table 2.
12. Repeat step 11 using the Magnesium, then with the Calcium. Look VERY CAREFULLY at the metal + water combo and
remember to touch the top of the petri dish to determine if heat can be detected.
13. Rate the reactivity of each of these samples with water, and record in data table 2.
14. DO NOT DISCARD THE Aluminum or the Magnesium strips—they will be re-used by the next class. The reacted calcium is
to be rinsed into the Calcium Waste container on the center table.
15. Rinse each of the petri dishes with water and place upside-down on the lab table.
Part 3: Comparing reactivity of group 1 metals
16. In the fume hood, the instructor will allow the class to observe a piece of sodium and potassium (or lithium). Note the
appearance of the “outside” of the sample versus the “inside”.
17. Each sample will be exposed to water with a drop of phenolphthalein. Record signs of a chemical reaction. Rate reactivity
level.
18. The remainder of the samples will be viewed in a short video clip. Again, rate the reactivity level of alkali metals and record in
Data Table 3.
Observations:
Data Table 1: Exposure to Oxygen and/or Heat for Al, Mg, and Ca
Sample
Initial Appearance
Appearance after
burning
Evidence of reaction of ash
with water/phenol
Rate reactivity level with
oxygen (1 = most reactive)
Aluminum
Magnesium
Calcium
Data Table 2: Exposure to Water for Al, Mg, and Ca
Sample
Aluminum
Magnesium
Calcium
Evidence of Reaction with Water
Rate reactivity level
with water (1= most
reactive)
Name: ______________________________________________ Date: _____________ Hr: _______
Data Table 3: Alkali Metals exposure to water
Sample
Initial Appearance
Evidence of reaction when
exposed to water/phenol
Rate reactivity level with water
(1= most reactive)
Li
Na
K
Rb
Cs
Post-Lab Questions:
1.
Which samples reacted with oxygen? Choose all that apply: Al, Mg, Ca, Na, K
2. Which samples reacted with water? Choose all that apply: Al, Mg, Ca, Na, K
3. Which samples were the MOST reactive with oxygen and water? Least reactive?
4. Explain why certain metals were more reactive that other members of its group based on stable electron configuration and
trends in atomic radius and ionization energy.
5. Sodium, Magnesium, and Aluminum are in Period 3. Which metal was most reactive? Explain why based on based on stable
electron configuration and trends in atomic radius and ionization energy.
6. Determine a trend for level of reactivity within a group of metals—where would one expect to find the most reactive metal in a
group? Why?
Name: ______________________________________________ Date: _____________ Hr: _______
7. Consider a group of nonmetals. Where would one expect to find the most reactive nonmetal in a group? Why?
8. Examine the diagram of successive ionization energies (in kJ/mol)below, then respond to the questions that follow.
Element
1st
2nd
3rd
4th
5th
6th
7th
8th
Na
500
4,500
5,000
5,500
6,500
7,000
7,500
8,200
Mg
700
1,400
7,700
8,300
9,000
10,500
11,200
11,900
Al
600
1,800
2,400
11,600
12,200
12,800
14,000
14,600
X
1,000
3,000
4,000
5,000
8,000
9,000
27,000
28,000
a. Why does it ALWAYS take more energy to remove the 2nd electron than the 1st (or more energy to remove the 3rd
electron than the 2nd, and so on)?
b. Compare the percent increase between Aluminum’s 1st and 2nd ionization energy versus the 2nd and 3rd ionization
energy versus the 3rd and 4th. Where are the significant leaps? Why do these electrons require so much more energy
to remove than the preceding electrons?
c. Assuming each of the elements in the table are from Period 3, which element is X? Explain.