Mystery Solution Identification
Subject Area: Chemistry
Grade Level: High School Chemistry
Lesson Title: Mystery Solution Identification
National Science Standards:
 Science as Inquiry: 9–12
Physical Science Standards:
 Structure and Properties of Matter: 9–12
 Chemical Reactions: 9–12
Suggested Prior Knowledge: concepts of solubility rules, precipitation reactions, double
replacement reactions, net ionic equations
Purpose: To understand solubility rules and use this knowledge to identify unknown
solutions
Key Vocabulary:
double replacement reaction—a chemical change in which two compounds
exchange ions; sometimes also called double displacement reaction.
precipitate—a solid that forms and settles out of a liquid mixture.
solubility—amount of a solute that will dissolve in a given quantity of solution,
usually measured in grams/100 ml solution.
Objectives:
1. Students will be able to predict the products of a double replacement reaction and
determine if a precipitate will from.
2. Students will use their data and observations and their knowledge of solubility
rules and double replacement reactions to determine the identity of several
unknown solutions.
3. Students will observe the reactions of the unknown solutions.
Materials:
- Safety goggles
Mystery Solution Identification (High School Level)
- Reaction surface (plastic sheet protector)
- Droppers or pipettes
- Several unknown solutions (number can vary depending on time available)
 Copper (II) sulfate
 Iron (III) chloride
 Magnesium sulfate
 Silver nitrate
 Aluminum chloride
 Sodium phosphate
 Sodium carbonate
 Ammonium hydroxide
 Cobalt (II) nitrate
 Barium nitrate
(Note all solutions should be 0.10 M)
- Unattached labels to be matched to the unknown solutions
Procedure:
1. Discuss with students the following scenario. They have been hired as new chemistry
teachers at a school. When they arrive they find the storage room is in disarray. While
trying to organize the chemicals and supplies they come across several solutions in
bottles without labels. They also find an identical number of labels that appear to have
fallen off of the unlabeled bottles. They need to determine the identity of these solutions
so they can dispose of them properly (and most importantly, safely).
2. Discuss with students how we can design a valid investigation that will allow them to
use their knowledge of chemistry and solubility rules to identify the solutions and
determine how to properly dispose of them. Begin with a leading question, and followup:
 What do we know about the reactions of these possible solutions?
 What do we know about the properties of these possible solutions?
 Are any of the solutions colored?
 Do we know that any of the labels match colored solutions?
 What kind of investigation can we do to determine which of the unlabeled
solutions is which?
 How can we determine how to safely dispose of these solutions once we can
identify them?
3. Work with students to design a valid investigation, similar to the one outlined in this
lesson, that will allow them to use the physical and chemical properties of the solutions
on the labels to match each label to the correct unlabeled solution. Students should be
sure their procedure is detailed and they should create appropriate data tables for their
data and observations. All student procedures should be approved by the teacher before
students begin any lab work.
4. A possible procedure to follow includes the following steps:
Mystery Solution Identification (High School Level)
a. Begin by observing the unknown solutions. If any are colored, research which of the
unknown solutions are known to be colored. Record this possible identification.
b. Predict the products for all of the possible combinations of solutions and write the
balanced chemical equations for reaction.
c. Using your observations and a solubility table, identify which combinations produce
precipitates.
d. Identify which, if any, of the possible precipitates are colored.
e. Using a plastic sheet protector as a reaction surface, carefully combine 1–2 drops of
each solution with 1–2 drops of all of the other solutions and record your observations.
f. Use observations and data to determine which of the unknown solutions matches each
of the labels.
g. Use MSDS information or the Internet to research the proper disposal method for each
solution.
5. Other possible methods students might try include the following:
a. Students may test the pH of the solutions and try to match these to known pH values
for the solutions.
b. Students may try to react the solutions with a dilute (0.10M) hydrochloric acid solution
to watch for bubbling of carbonates.
c. Students may react the unknown solutions with other known solutions available in the
lab.
d. Students may react the unknown solutions with various metals and use an activity
series to try to identify the metal cation in the unknown solutions.
6. Lab safety equipment and protocols should be followed. Goggles should be worn at all
times.
7. After the students have finished their investigations, they should be able to identify the
unlabeled solutions and describe how to dispose of each correctly.
8. Students may present their findings to their classmates using slideshows or posters.
Additional Resources:
http://www.flinnsci.com/Sections/Safety/safety.asp
http://www.flinnsci.com/search_MSDS.asp
http://antoine.frostburg.edu/chem/senese/101/reactions/faq/predicting-products-nicl2nh42s.shtml
http://dl.clackamas.edu/ch105-04/precipit.htm
http://chemistry.about.com/od/solutionsmixtures/a/solubility-rules.htm
http://www.ehow.com/how_6829504_disposal-lab-chemicals.html
Mystery Solution Identification (High School Level)
Student Worksheet for Mystery Solution Identification
Experiment Title: _____________________________Date: _______Name: __________
Student Hypothesis: _______________________________________________________
Materials:
Safety goggles
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Safety Precautions:
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Procedure:
Wear safety goggles for all lab work.
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Mystery Solution Identification (High School Level)
Data and Observations:
Analysis of Data: _________________________________________________________
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Mystery Solution Identification (High School Level)
Conclusions: _____________________________________________________________
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Mystery Solution Identification (High School Level)