Name: ______________________________________________ Date: _____________ Hr: _______
H Chem 10-11 Lab: Comparing Reactivity of Metals within a Group
Objective: This lab will consist of two sections, with part 2 using demonstrations and a video. In part 1 you will be
gathering data to compare chemical properties of unknown metal samples when exposed to the oxygen in the air and
water. In part 2, you will observe the behavior of alkali metals when exposed to air and water.
Pre-Lab Question: 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 has the potential to react body tissue due to high water
content in the body. A small amount of heat and flammable gas will be produced—follow directions in order to prevent
exposure. No open flames!
Materials: 4 petri dishes (top and bottom), labeling paper, wash bottle, forceps, four metal samples
Procedure & Results
Part 1: Test each of 4 unknown metal samples for reactivity with oxygen and then water.
Test 1: Observe reactive to oxygen
1. Dry each petri dish top and bottom.
2. Label different pieces of marking paper A, B, C, and D to organize metals. Place the paper under the bottom of
the petri dish
3. Obtain samples of each metal from instructor and place in the LIDS of the open petri dishes. Do NOT place the
lids on the bottoms!
4. Metals tend to form “oxides” when exposed to oxygen. You are familiar iron oxide, or rust. Metals tend to be
lusterous (i.e. shiny), but areas exposed to oxygen will form a dull coating over time. Each of the metal samples
have been exposed to oxygen for the same period of time. Examine the surface of each metal sample and record
observations in the part 1 data table. Eventually you will be ranking the metals based on this quality so make
careful observations.
Data Table Test 1: Exposure to Oxygen
Sample
Description of Metal Surface
Rank—1 is most reactive
with oxygen
A
B
C
D
Test 2: Reactivity with Water
5. Your metal samples should be in the lids of the petri dish. 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—if
it does you need to rinse and dry the dish). Since the metal samples are currently in the petri dish top (not the
bottom), the samples should not yet be exposed to water. I cannot possibly make it any more clear that the metals
Name: ______________________________________________ Date: _____________ Hr: _______
are in the lid and the water is in the bottom…please don’t be ‘that’ group who demonstrates the inability to follow
directions…there will be a penalty 
6. Beginning with sample A, add sample A to the water by flipping the top of the petri dish onto its bottom so the
metal sample falls into the water and the lid is now covering the bottom of the petri dish. These metals will form
bases IF they react with the water. We will know if the metals are reacting with water because phenolphthalein
will turn a shade of pink if a base is present (usually starts around the edge of the metal sample). This reaction (if
it occurs) will also produce hydrogen, and would be an exothermic reaction. Observe for two minutes over the
white paper, then record observations in data table 2. You should touch the lid to determine if there is a change in
energy (temperature).
7. Repeat step 6 using samples B-D. 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.
8. Compare the reactivity of each of these samples with water, and record in data table 2.
9. Your team is awesome if you save the metal samples which did not react to be re-used by the next class. The
reacted metal is to be rinsed into WASTE container on the center table.
10. Rinse each of the petri dishes with water and place upside-down on the lab table.
Data Table Test 2: Exposure to Water
Sample
Evidence of Reaction with Water (look for signs of a chemical reaction)
Rank reactivity—1 is
most reactive with water
A
B
C
D
Start Post lab Questions 1 and 2
Part 2: Comparing reactivity of group 1 metals with Oxygen and Water via demonstration and video clip
11. 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”. Keep in mind these are metals, which
should be shiny! Record observations in ‘evidence of reaction with oxygen’ portion of the data table.
12. Each sample will be exposed to water with a drop of phenolphthalein. Record signs of a chemical reaction in
water in ‘evidence of reaction with water’ portion of the data table.
13. 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.
14. Rank the reactivity of observed alkali metals, with #1 being the most reactive.
Name: ______________________________________________ Date: _____________ Hr: _______
Data Table 3: Alkali Metals exposure to oxygen and water…
Sample
Evidence of exposure to oxygen
Evidence of reaction when exposed
to water/phenol
Compare reactivity when
exposed to water
Li
Na
K
Rb
Cs
Post-Lab Questions:
1. Based on patterns of reactivity, which of the 4 metal samples tested in part 1 were members of the same group on
the periodic table? Justify your claim with evidence from your part 1 data tables.
2. Obtain the identities of the four metal samples from the instructor. For the metals which were in the same group
of the periodic table, which metal was more reactive? Compared to the less reactive member of the same group, is
the more reactive element above or below the less reactive element?
3. Describe the pattern of reactivity as atomic number increases in the alkali metals.
4. When each of the tested metals reacted with oxygen or water, the metals gave up electrons to form cations. If ‘M’
represents the metal, the reaction would look like this:
M  M +# + #efor example, Magnesium would be Mg  Mg +2 + 2 eTherefore, we can conclude metals which were more reactive in the lab (and real life) give up electrons more
easily than less reactive metals. Ionization energy is a measure of the amount of energy needed to remove
electrons from atoms. Explain why certain metals were more reactive than other members of its group based on
ionization energy. Your response will must include which atom has a higher ionization energy and why, and how
this ionization energy relates to reactivity.
Name: ______________________________________________ Date: _____________ Hr: _______
a. Mg and Ca—which was more reactive and why
b. Li, Na, K, Rb, Cs—which was more reactive and why?
c. Determine a trend for reactivity level within a group of metals—where would one expect to find the most
reactive metal in a group? Explain why.
5. Two groups were examined—alkali metals and alkaline earth metals. Which of these two groups was more
reactive with oxygen and water? Explain why based on ionization energy.
6. Sodium, Magnesium, and Aluminum are in Period 3. Which of these three metals is most reactive with oxygen
and water? Explain why based on ionization energy. To clarify, you are now comparing reactivity of metals
across a period (left to right).
7. Consider a group of nonmetals. Where would one expect to find the most reactive nonmetal in a group? Why?