Qualitative

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					                                                                           Freshmen Research Initiative
                                                                                         Nano Stream
                                                                                          Spring 2009


                               QUALITATIVE ANALYSIS

LECTURE TOPICS


GOAL

In this experiment, you will learn to make observations, and to record your observations
scientifically. You will also use your observations to qualitatively identify unknown solutions.


INTRODUCTION

Identifying samples of unknown substances is an important part of chemistry, with applications
in such fields as medicine, environmental science, and geology. Materials can be characterized
by their chemical reactions and by methods involving instruments. Often identification of
substances by their typical reactions is easy, quick, accurate, and inexpensive in comparison to
the instrumental methods. The most important source of information about the solutions’
contents is observation of the chemical reactions that take place when the solutions are mixed.
Your observations of color changes, precipitation, complex ion formation, evolution of gaseous
species, or lack of any observable reaction will provide the information necessary to determine
the solutions’ identities. In order to identify chemicals based on reaction observations, a detailed
and organized experimental record is essential.

In this experiment, you will first make observations of known reactions by mixing solutions of
known composition. You will then use your observations from mixing the known solutions to
identify the compounds in eight unknown solutions. Each known and unknown solution contains
one compound with a concentration of approximately 0.1 M.

All the reactions in this experiment will be conducted in a 96-well-plate to reduce the amount of
waste, and to save on the amount of chemicals consumed. The volume of each well in a 96-well
plate is approximately 0.5 ml. To do a reaction in a well plate, add 2-3 drops of each solution to
be tested. Notice that the well plate is labeled with letters and numbers to simplify keeping track
of combinations.


PROCEDURE

I.     Observing reactions of known solutions (You may work with a partner on this part,
but please keep individual record of the observations)

Binary-mix (i.e. mix one solution with the other) the following 14 solutions listed in the table
below in a drop-wise manner in a well-plate, one binary mixture per well.




                                      Experiment #2 02/02/09
                                                                           Freshmen Research Initiative
                                                                                         Nano Stream
                                                                                          Spring 2009

Construct a data table similar to the one shown below (Table 1). Record your observations,
especially any color changes, and/or formation of precipitates or gases. Make sure the table is
large enough to record all your observations. You are advised to use an entire page in
“landscape” style for this table. You may create a recording system to simplify your table (e.g.:
“wh. ppt.” to represent the formation of “white precipitates”, or “” to indicate gas formation,
etc.).

If the solution is clear AND one of the components is an acid (e.g.: HCl, HNO3), use a strip of
pH paper to test the mixture acidity. Use the color code on the pH paper case to identify if the
mixture remains acidic (pH < 7). If not, an acid-base reaction has taken place. Record the pH of
all acid mixtures in your table.

If you are in doubt about a reaction, feel free to repeat it.




                                     Table 1. Binary mixture chart

Note I: To prevent cross-contamination of solutions in the drop bottles, do not dip the tip of the
dropper into the solutions in the well plates.

Note II: It might help to observe the formation of any white precipitate by placing the well plate
on a dark colored background.

Note III: Discard the well contents in the designated waste jar, and rinse the well plate
thoroughly with DI water. Dry out the wells with paper towels before adding new solutions for
more tests.




                                        Experiment #2 02/02/09
                                                                          Freshmen Research Initiative
                                                                                        Nano Stream
                                                                                         Spring 2009

Q.1. Consider your experimental observations. Pick 15 of your favorite reactions, and write their
net ionic equations.

II.    Unknown identifications (Obtain your individual unknown rack from your lab
instructor or TA)

   1. Unknown #1 is one of the 14 solutions you have used above. To identify this unknown,
      binary-mix it with the 14 known solutions in the same manner as before. Construct a new
      table in your lab notebook that is organized like Table 2, shown below. Record your
      observations in the “Unknown #1” row of this table. Identify the unknown.




                                  Table 2. Unknown identifications

Note IV: To prevent cross-contamination, use a new disposable pipet (plastic or glass) for each
unknown solution.

   2. Unknown #2 is a nitrate salt whose cation is one of the cations present in the 14 known
      solutions. Your task is to identify the unknown cation only. Binary-mix unknown #2
      with the 14 known solutions. Record your observations in the table in your notebook.
      Identify the unknown.

Note V: This is somewhat more difficult than your first unknown. The results may not
completely match up with any of the knowns. For example, consider the column of CuSO4
reactions. Some of the reactions in this column are due to Cu2+, and others to the sulfate anion.
If your unknown is Cu(NO3)2, you would expect it to match up with the reactions due to Cu2+,
but not to the sulfate.

   3. Unknown #3 is a sodium salt whose anion is one of the anions present in the 14 known
      solutions. Your task is to identify the unknown anion only. Binary-mix unknown #3
      with the 14 known solutions. Record your observations in the table in your notebook.
      Identify the unknown.

   4. Unknowns #4~#8 are selected from the known solutions. Binary-mix these five
      unknowns only with each other. Construct a table in your notebook in the format of
      Table 3, below, and record your observations. Try to identify the unknown solutions
      from just the binary-mixing results.




                                      Experiment #2 02/02/09
                                                                              Freshmen Research Initiative
                                                                                            Nano Stream
                                                                                             Spring 2009




                               Table 3. More unknown identifications

    5. If you have doubt about your determination of the 5 unknowns, use any additional tests
       that you want to run to clarify the identity. Make sure you record in your notebook in
       detail which additional reactions you choose to run.


Q.2. On a separate page in your notebook, list your unknown codes and your conclusions of
their identities.


WASTE DISPOSAL
   Waste Chemicals                             Disposal                              Location
Well plate contents               Plastic waste container              In the hood
Extra unknown solutions           Return to your TA




BEFORE COMING TO LAB

       Read and print out the lab experiment.
       Familiarize yourself with a solubility table (online or from your General Chemistry
        textbook). Print out a copy and paste it on your lab notebook as part of your pre-lab
        preparation. This will be helpful to complete the lab.
       Regenerate Tables 1-3 in your lab notebook



WHAT TO TURN IN

       Answer questions 1 and 2 in your lab notebook
       Carbon copy of the lab notebook with your raw data, tables, and answers to the questions




                                      Experiment #2 02/02/09