Behavior of Two Families of the Periodic Table
This experiment was largely assembled from the two experiments listed below with
modifications:
http://plaza.ufl.edu/ctoyota/Expt9_redox.pdf
http://faculty.ccri.edu/eterezakis/1030%20Exp%2005,%20Two%20Families%20of%20the%20
Periodic%20Table.pdf
Introduction
The periodic table arranges the chemical elements in order of increasing atomic number in
horizontal rows of such length that elements with similar properties recur periodically, i.e., they
fall directly beneath each other in the table. The elements in a given vertical column are
referred to as a group or a family. By noting the trends in the properties of a family of elements
or their compounds, it is possible to arrange them in the order in which they fall in the periodic
table. In this experiment, you will do this for two families of elements by studying trends in the
properties of their compounds.
The two families to be studied are the “alkaline earths” or Group 2 (formerly Group IIA) metals
and the halogens, Group 17 (formerly Group VIIA). Group 2 encompasses the active metals
barium, beryllium, calcium, magnesium, radium and strontium. Beryllium compounds, rarely
encountered, are often toxic and all radium isotopes are highly radioactive, so we shall not
include these two elements in the experiment. The halogens are astatine, bromine, chlorine,
fluorine and iodine. Of these, we omit astatine, which is radioactive and extremely rare, and
fluorine, some of whose compounds are toxic.
The Group 2 metal ion experiments will determine the solubility of salts formed by the metal
cations with the sulfate, carbonate, oxalate and chromate anions. When solutions containing
these M2+ cations are mixed with the A anions, the reaction shown below will occur if the salt
MA is insoluble in water. Here M2+ stands for Ba2+, Ca2+, Mg2+ or Sr2+ and A stands for SO4-2,
CO3-2-, C2O4-2 or IO3M2+ (aq) + A(aq)  MA(s) (Equation 1)
Given the properties of Group 2 metal cations and the properties of halide anions observed in
this experiment, it is possible to identify a Group 2 cation and a halide ion in a solution. Your
unknown solution will contain one Group 2 halide salt consisting of a single Group 2 cation and
a single halide anion.
Experimental
Obtain an unknown solution and record its number on your data sheet. Your unknown will be a
salt solution consisting of a single Group 2 cation and a single Group 17 (halide) anion.
1. Relative Solubilities of Group 2 Salts:
a) Put about 1 mL (approximately 12 drops) of 0.1 M barium, calcium, magnesium and
strontium nitrate solutions into separate small or medium test tubes. Put 1 mL of your
unknown solution into a fifth test tube. To save time, do not measure the solutions in a
graduated cylinder. Use the supply bottle droppers to transfer 12 drops of each solution. Pencil
the cation formula onto the white patch of each test tube. To each test tube, add 1 mL (12
drops) of the precipitating reagent 1 M H2SO4 and briefly shake the test tube gently from side
to side to mix the contents. Record your observations, stating whether a precipitate forms, as
well as characteristics that distinguish the precipitate. (A precipitate may consist of a dense
solid in the bottom of the test tube, a fluffy solid or simply a new cloudiness in the liquid.)
Discard each mixture as heavy metal waste. Between procedures, rinse each test tube twice
with a few mL of distilled or deionized water and discard the rinse water as heavy metal waste.
Shake excess water out of each test tube before you go to the next procedure.
b) Repeat the experiment in five clean test tubes with fresh 1 mL portions of the Group 2
nitrate salt solutions and your unknown solution with the precipitating reagent 1 M Na 2CO3.
c) Test fresh 1 mL portions of the Group 2 salt solutions and your unknown solution with 1 mL
portions of 0.25 M (NH4)2C2O4.
d) Test fresh 1 mL portions of the Group 2 salt solutions and your unknown solution with 1 mL
portions of 0.25 M KIO3.
PART II Reactions of halide ion solutions with halogens
A. Preliminary Observations:
The visual clue you will have for this part of the investigation is the color that halogens exhibit
when they are dissolved in hexane. First, you will investigate the properties (solubility and
color) of the halogens in solution with water and with hexane. Next you will use this
information to probe what happens when a halogen is mixed with a salt of a different halide.
CAUTION: The halogens are all good oxidizing agents and can cause burns. Take extra care
with their solutions.
Label six small test tubes and place into them 1 mL each of the chlorine water (Cl2), bromine
water (Br2), iodine water (I2), 0.1M NaCl solution, 0.1M NaBr solution, and 0.1M NaI solution,
respectively. Observe the appearance of each solution including its color and record this
information under aqueous solution in the table below. Then add 0.5 mL of hexane to each
tube, stopper, and shake well to mix using a stopper in the test tubes (no thumbs!).
Observe the appearance of both layers in each tube. Which layer is which? Try to figure this
out. Be sure to follow instructions for the safe disposal of these solutions.
Record the colors of the halogen / halide ions in water and hexane.
Based on color can you say something about the solubilities of the halogens, as a group, in
water versus hexane?
Based on color alone can you say something about the solubilities of the halides, as a group, in
water versus hexane?
Now that you know what colors to expect for each of the halogens and halide ions in both
water and hexane, you can determine the results of any of the six possible combinations where
a reaction might occur. (Of course, three additional combinations, such as mixing Br2 and Br-
solutions will not result in any changes.) You will be given specific instructions below for one
such combination; it is up to you to decide how to perform the rest of the tests.
B. Testing Halogen Oxidizing Strengths:
Pour 1 mL of chlorine water into a test tube. Add 1 mL of 0.1M NaBr, stopper and mix. Note any
changes.
Next add 1 mL hexane, shake, and again note any changes. Which halogen is now present?
Which is higher in the activity series, Cl- ion or Br- ion?
The reaction under investigation is:
Cl2 (aq) + 2 Br - (aq)  Br2 (aq) + 2 Cl -(aq)
Label (in the spaces provided) the oxidizing agent and conjugate oxidizing agent in the reaction
above. By observing and recording the color changes in both layers, decide which is the
strongest oxidizing agent. Try all possible combinations given in the following table below,
following a procedure similar to the one above.
Write the equation that describes the reaction for each system in which you observed a change.
Rank the halogen molecules in order of decreasing oxidizing agent strength. (Use the > symbol
to rank them.)
Now write the activity series for the halide ions as reducing agents. (Use the > symbol to rank
them.)
Would you expect a reaction to occur between At2 and I- ? Explain.