CHM120 Periodic Trends Lab
Group Trends for Halogens
The Periodic Table is one of the useful tools in chemistry. The table was developed
around 1869 by Dimitri Mendeleev in Russia and Lothar Meyer in Germany. Both used
the chemical and physical properties of the elements and their tables were very similar.
In vertical groups of elements known as families we find elements that have the same
number of valence electrons such as the Alkali Metals, the Alkaline Earth Metals, the
Noble Gases, and the Halogens.
One of the groups of focus in this experiment is the Halogens. These elements have a
high affinity for electrons and show a strong tendency to gain electrons from other
elements to form the halides.
X2 + 2 e- --> 2 X where X2 is the Halogen and X - is the Halide
Cl2 + 2 NaBr --> 2 NaCl + Br2
Cl2 + 2 Na + + 2 Br - --> 2 Na + + 2 Cl - + Br2
Cl2 + 2 Br - -->
2 Cl - + Br2
Chlorine, Cl2 , gains electrons from the bromide ions Br - to form 2 chloride ions Cl- and
bromine Br2 . In turn each bromide ion loses one electron to form bromine Br2 . Sodium
Na is a spectator ion in the above reaction.
The halogen X2 is nonpolar (not charged) and will be extracted into the organic solvent
(nonpolar phase). The halide X - is a charged species (polar) and will be extracted into
the aqueous phase (polar phase). The organic solvent is less dense than water and will
be the top layer of the two phases.
Organic
Phase
X2
Aqueous
Phase
X-
Each element has been assigned an Electronegativity value based on its ability to
attract electrons to itself. (See the Table of Electronegativity values in our textbook.)
The greater the Electronegativity value EN, the greater the ability an element has to
attract electrons.
The periodic trends of several metals will also be investigated in this experiment. Unlike
halogens, metals tend to lose electrons. Magnesium, calcium, and aluminum will be
reacted with water and acid to determine trends in metal activity within a group and
across a period of the periodic table. Locate each of these metals on the periodic table
and identify the group that each belongs to.
Objectives
1.
2.
3.
4.
5.
6.
Observe the color for Halogens (Group VIIA) in an organic solvent.
Investigate extractions
Determine whether a reaction has occurred
Investigate the reactivity order of the halogens (which halogen is more reactive).
Investigate the reactivity order of several metals (which metal is most reactive)
Compare the Halogens to other oxidizing agents such as KMnO4 and FeCl3 .
Prior to lab read the sections of our textbook that address periodic trends in atomic
radius, electronegativity values, and the periodic table.
In this experiment you will be asked to determine if a reaction has taken place.
Remember there are several indications that a reaction has occurred. Formation of a
solid or a gas are some observations of a reaction; as is the absorption or release of
energy (in the form of heat or voltage) or the change in color of the solution. In this
experiment color changes will be observed to identify when a reaction has taken place.
Equipment:
6 - 13x100 mm test tubes
6 - stoppers to fit small test tubes
Small test tube rack
Test plate
Digital thermometer
Forceps
pH paper
Chemicals:
Cyclohexane
Chlorine Cl2
Bromine Br2
Iodine I2
Solutions of NaCl, NaBr, NaI
Magnesium ribbon, calcium turnings, aluminum foil
Dilute 0.5 M hydrochloric acid
This experiment will contain several parts. Each part has a worksheet to enter collected
data and record observations.
1.
2.
3.
4.
Color of the Halogens
Reactions with the Halides
Reactions of Halides with other compounds
Reactions of metals
Download Periodic Trends Spreadsheet
Part 1: Determining the Color of the Halogens
1. Wash and dry the small test tubes.
2. Place 15 drops of Chlorine water in one test tube, 15 drops of Bromine water in
another test tube and 15 drops of Iodine water in a third. Label each test tube.
3. Add 1.0 ml of cyclohexane, stopper and shake very gently.
4. The color of the halogen will appear in both the upper cyclohexane layer and the
lower water layer; sometimes the halogen color is the same in both layers but
most often the halogen color is different in water from that in cyclohexane.
Against a white background, view the color of each halogen in each layer – the
color of the cyclohexane (top layer) and the color of the aqueous bottom layer.
Record the colors on the data page.
Part 2 : Predictions of Halogen Reactions with the Halides
1. Using the data from Part 1, write the color of the Reagent Halogen X2 found
in the top layer for each combination listed. Remember: halogens are X2 and
halides are X - .
2. Make predictions of the possible reaction products and the color of the Product
Halogen X2 that will be extracted into the top layer. (See the reactions shown
above). Use the data from Part 1 to determine the expected color for the halogen
in the top layer.
Observations of Reactions with the Halides
Bromine Br2 with halides, NaCl and NaI:
1. Wash and dry the small test tubes.
2. Place 10 drops of bromine water in each of 2 test tubes.
3. Add 10 drops of 0.20 M NaCl to the first test tube and 10 drops of 0.40 M NaI to
the second one. Label each test tube.
4. Add about 1.0 ml of cyclohexane to each of these test tubes, stopper and shake
gently, and record your observations for the color of the top cyclohexane layer
after the reaction has proceeded.
5. Dispose of the solutions in the waste container for halogens.
Iodine I2 with halides, NaCl and NaBr:
1. Wash and dry the small test tubes.
2. Place 10 drops of iodine water in each of 2 test tubes.
3. Add 10 drops of 0.20 M NaCl to the first test tube and 10 drops of 0.20 M NaBr to
the second one.
4. Add about 1.0 ml of cyclohexane to each of these test tubes, stopper and shake
gently, and record your observations for the color of the top cyclohexane layer
after the reaction has proceeded.
5. Dispose of the solutions in the waste container for halogens
6. Wash and dry the small test tubes.
Chlorine Cl2 with halides, NaBr and NaI:
1. Place 10 drops of chlorine water in each of 2 test tubes.
2. Add 10 drops of 0.20 M NaBr to the first test tube and 10 drops of 0.40 M NaI to
the second one.
3. Add about 1.0 ml of cyclohexane to each of these test tubes, stopper and shake
gently, and record your observations for the color of the top cyclohexane layer
after the reaction has proceeded.
4. Dispose of the solutions in the waste container for halogens .
5. Fill in the other two color columns - that of the Reagent Halogen color in the top
layer and that of the Product Halogen color in the top layer.
6. Wash and dry the small test tubes.
To determine if the reaction actually occurred and produced products:
compare the actual color of the top layer to the colors of both the Reagent and
Product Halogens in the top layer. If the actual color of the top layer matches that of
the expected Product color, then the reaction did occur to produce the product.
Use the data from this section to answer the summary questions on the data sheet.
REACTIVITY OF METALS
The purpose of this experiment is to identify periodic trends in the reactivity of metals.
The reactions of magnesium, calcium, and aluminum with water and acids will be
compared in order to determine the trend in metal activity within a group and across a
period in the periodic table.
Materials:
Aluminum foil
Calcium turnings
Magnesium ribbon
Deionized water
0.5 M Hydrochloric acid
pH paper
Forceps
Spatula
Thermometer
Caution:
Calcium and magnesium are reactive, flammable solids and possible skin irritants. Use
forceps or a spatula to handle these metals.
Hydrochloric acid is corrosive to skin and eyes.
Procedure:
1. In a small weighing tray, place 2 small pieces of calcium turnings. Label this Ca.
2. In another tray, place 2 small pieces of magnesium ribbon. Label this Mg.
3. Tear off two 1 cm2 pieces of aluminum foil and roll each into a loose ball. Place
the aluminum foil in another tray.
4. Place a test plate on top of a sheet of paper with rows labeled A and B and
columns labeled 1 - 3.
5. Use an eyedropper to add 20 drops of distilled water to wells A1-A3.
6. Test the water in wells A1-A3 with a piece of pH paper and record the initial pH in
the data table.
7. Use forceps to add one piece of calcium to well A1 and one piece of magnesium
ribbon to well A2. Add the aluminum metal to well A3.
8. Observe each well and record all immediate observations in the data table. If no
changes are observed, write NR (No Reaction) in the data table.
9. Re-test the water in wells A1-A3 with a piece of pH paper and record the pH in
the data table.
10. Continue to watch each well for 1-2 minutes. Record any additional
observations, especially comparing the rates of reaction (how quickly each metal
reacts).
11. Use an eyedropper to add 10 drops of 0.5 M HCl to wells B1-B3. Measure the
initial temperature of the solutions in well B1-B3 and record the values in the data
table.
12. Do ONE metal at a time. Use forceps to add one piece of calcium to well B. Later
add one piece of magnesium ribbon to well B2. Tear off a 1 cm2 piece of
aluminum foil and roll it into a loose ball. Add the aluminum metal to well B3.
13. Observe each well and record all immediate observations in the data table. If no
changes are observed, write NR in the data table.
14. Using a thermometer, measure the temperature of each solution in wells B1-B3.
Record the final temperature of each solution in the data table.