Lesson written by Carolina Sylvestri
Experiment: Reaction Between Ions in Aqueous Solutions
The Monster Mash
Background: Ionic solids dissolve in water to form aqueous solutions which
conduct electricity. These solutions contain both positive and negative ions in
such numbers that their net electric charge is zero. In this experiment, you will
mix various ionic solutions, two at a time, to determine which combinations form
precipitates. Knowing which ions are present makes it possible to deduce which
of the possible ion combinations are responsible for the precipitates. From your
data table, it will then be possible to generate a solubility table.
Advice and general procedure: You must follow the directions for the prelab,
and you must perform the experiment carefully. Your five data tables should
each be on the upper ¾ of a separate side of paper. Each set should be labeled
as indicated on the sample table. All students will do sets 1-5. You must do sets
1 and 2 before doing sets 3, 4, 5. We will not have enough reagents for all teams
to work with the same set at the same time. Be flexible: have all five data tables
ready to complete and keep the sets organized. Each set has it own labeled well
plate. Do not contaminate the plates. You and your classmates should then be
able to communicate by asking, “did you get a beautiful blue ppt in Set #? Box
8?” You are responsible for being able to describe the color of each solution and
to recognize precipitate colors. It is a real advantage to you if you think about
molarity (solution concentrations) and drop ratios. Try to identify the excess
reagents and the proper mole ratios for maximum precipitate production.
Procedure:
1) See the sample diagram for how to number boxes and where to write the
predictions.
2) Before coming to class, write the formulas for the possible products in the
upper right portion of each of the boxes. If there is a common cation or a
common anion, note: no reaction (NR) and the reason
3) Before beginning the lab, note the color of each of the reagent solutions.
4) Each plate has been labeled with the appropriate set number. To avoid
contamination, use only the correctly labeled plate and wells. To begin, place
three drops of each reactant in the appropriate well. Be careful to keep the tip
of the bottles out of the solution. Occasionally, it’s necessary to change the
drop ratio or the drop order. (Look at the molarities, even write an equation,
and think.)
5) Continue testing pairs of solutions until all possible combinations of a set
have been tested. Describe the color and appearance of all precipitates. Try
to note the difference between opaque, cloudy, chalky. Some reactions take
longer to develop.
6) When finished with each set, turn the well plate upside down onto a piece of
paper toweling. Gently hit the well plate to release the solutions and
precipitate. Add small amount of distilled water to the used wells and “hit” the
plates only toweling. Do not rinse the plates with tap water. Why?
7) Return well plates to the well plate container. If needed, stained plates may
be rinsed using acetic acid followed by distilled water.
ORDER OF REAGENTS AND MOLARITIES FOR EACH SET
Set #1
0.1M Ba(NO3)2, 0.1M BaCl2, 0.2M K2CrO4,
0.1M K2SO4, 0.4M KCl
Set #2
0.2M Na2SO4, 0.14M Al2(SO4)3, 0.1M Sr(NO3)2,
0.2M MgCl2, 0.1M Ba(NO3)2, 0.07M AlCl3
Set #3
0.1M Co(NO3)2, 0.2M KOH, 0.2M NaNO3,
0.5M NaOH, 0.1M FeCl3, 0.1M CoCl2
Set #4
0.5M NaOH, 0.1M NiCl2, 0.14M Ba(OH)2,
0.2M MgCl2, 0.2M MgSO4, 0.2M Na2SO4
Set #5
0.1M Sr(NO3)2, 0.1M BaCl2, 0.14M Al2(SO4)3,
0.2M K2CrO4, 0.05M AgNO3
Sample data table:
Set 1
Ba(NO3)2
BaCl2
K2CrO4
K2SO4
KCl
Ba(NO3)2
BaCl2
K2CrO4
K2SO4
KCl
Processing the data:
For each set, include the following beneath the data table for that set.
1) You may assume that each precipitate formed was doe to a new combination
of the ions in the solutions. For example, if you mix aqueous solutions of
AgNO3 and NaCl, there are two new combinations of ions possible. The silver
nitrate solution contains Ag+(aq) and NO3-(aq). The sodium chloride contains
Na+(aq) and Cl-(aq). Possible new combinations of these ions are AgCl and
NaNO3. Note: these formulas would have been written in the upper right hand
corner of each box before beginning the lab.
2) Examine your data to see if you can justify eliminating some of the
combinations listed as possible precipitates in this experiment. For example,
NaCl was an aqueous product in Set 1-15. Therefore it could not precipitate in
another box or set.
3) Write equations to indicate what you consider to have happened in each case
in which there was precipitate formed. Use ions to represent the species in
the reacting solutions, but for those products that were precipitates write a
formula for the compound. Place (aq) after those species in solution and (s)
after the precipitates. Be sure to write the equations so that both atoms and
charge are conserved. For example:
Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq)  AgCl(s) + Na+(aq) + NO3-(aq)
4) Rewrite the equations, leaving out the ions not involved in the reaction
(spectators). Such an equation, which shows only the predominant reacting
species, is called a net ionic equation.
Ag+(aq) + Cl-(aq)  AgCl(s)
5) If you feel that you understand the concept, feel free to write only the unique
net ionic equations but indicate the set #s where the reaction occurred. Of
course, you will be able to do #3. At the bottom of each set, write the unique
net ionic equations for that set.
6) For each set note the reagents and soluble product.
After the completion of the five data tables and analysis:
7) Make a list (in the form of a data table) of soluble solutions (yes that is
redundant). Categorize by anion, then by increasing cation charge. Anions
should be listed alphabetically by increasing negative charge (ie, chlorides
come before nitrates which come before sulfates).
8) Conclusion: make a solubility table that includes all reactants and products
from the five sets in this lab. The table should be organized by anions using
the approach indicated above. Know the colors, solubilities, and products in
each box.
The following serves as a rough example for the conclusion table format
Anion
Phosphate (PO4-3)
Insoluble cations
barium, Ba+2, calcium, Ca+2
Soluble cations
sodium, Na+