Experiment 9: A Chemistry Investigation
Qualitative analysis in chemistry is very much like a detective game. The characters in a detective story have
methods of operation and other distinguishing features. These characteristics make it possible to identify
individuals as having been responsible for certain acts. The clues that one observes are evidence of some kind
of interaction. In qualitative analysis you will make use of clues, evidence of chemical interaction, to help you
identify the presence of specific ions in solution. However, before you can expect to identify the presence of
ions, you must first become familiar with their characteristic behavior (method of operation).
In this experiment you will be given four solutions, labeled 1, 2, 3, and 4. You will discover how they behave
when they are mixed with four reagents labeled A, B, C and D. By making careful observations you will detect
evidence of chemical reaction that will be characteristic for each of the solutions. These clues may be the
formation of precipitates, change in color, production of a gas, production of heat or other evidence of chemical
reaction. Recording your observations in tabular form will help recognize characteristic behavior for each of
the four solutions.
The solutions and reagents used in this experiment are deliberately identified by letter or number. This will
permit you to focus your attention on the reasoning involved in developing an analytical scheme rather than on
the actual reaction taking place. The scheme will permit you to identify unknown solutions according to their
differentiating properties.
Consider the following hypothetical case, reagents X, Y and Z, were allowed to react with a few drops of each
of the solutions I, II, III and IV. The observations were recorded in the table as shown.
SOLUTIONS/REAGENTS
X
Y
I
-
+ WHITE
II
+ WHITE
III
+ GASES
IV
-
Z
+ YELLOW
-
+ YELLOW
-
+ YELLOW
+ WHITE
-
The + means distinctive evidence of reactions was observed and a - indicates no observable evidence or
reaction. The color of precipitates or changes in color of solutions was also noted. If you were given an
unknown solution which you were told was like one the four solutions tested, what method would you outline to
identify the unknown? How many tests would you have to use? If another unknown gives a + test with X, is
this sufficient evidence to identify it as one of the four solutions?
Procedure
1. Obtain a set of solutions and reagents. Set aside a 400 mL beaker as a waste beaker.
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2. Using the height of a 2mL sample of water in a test tube as a reference, place about 2mL of solutions 1,
2, 3 and 4 into a set of four clean test tubes and label them as 1, 2, 3 and 4. Add about 2 mL of reagent
A to each test tube. Observe and record on the report sheet your results under the first column as + or –
and include a brief description of any characteristic property of the + test. Pay attention to the formation
of gases, precipitates, color changes or temperature changes of the mixtures.
3. Dispose the waste in the waste beaker, clean the test tubes. Place about 2mL of the solutions 1, 2, 3 and
4 to each test tube. Add about 2mL of reagent B to each test tube. Observe and record your results
under the second column as + or – and include a description of any characteristic property of the + test.
4. Continue performing tests on each of the solutions 1, 2, 3, and 4 using reagents A, B, C and D until you
have tested all possible combinations. Record your results as + or – and include a description of any
characteristic property for the + tests under the appropriate column of your table.
5. Study the data carefully and note the identifying clues. Obtain an unknown from your instructor.
Record your unknown number and test the unknown with reagents A, B, C and D to determine which
solution it is like. Report your analysis together with a summary of the supporting evidence.
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Chemistry Investigation
Report Sheet
SOLUTIONS/REAGENTS
Name: _____________________
A
B
C
D
1
2
3
4
SOLUTIONS/REAGENTS
A
B
UNKNOWN#
Which solution is your unknown? _________________________
Explain how you came to this conclusion.
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C
D
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Chemicals for this lab:
15mL /student in dropper bottles (at least 3 of each)
Label the following solutions as
Solution 1 for 1.0 M sodium carbonate
Solution 2 for 0.1M NaCl
Solution 3 for 0.1 M barium chloride
Solution 4 for 0.1 M lead(II) nitrate
15 mL/student in dropper bottles (at least 3 of each)
Label the following reagents as
Reagent A for 0.1M HCl
Reagent B for 0.1 M silver nitrate
Reagent C for 0.1 M sodium sulfate
Reagent D for 0.1 M potassium iodate
Unknowns:
10ml/ student from the solution 1,2,3 or 4. Please label them with unknown numbers.
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