 |
 |
11 of 19 |  |
 |
 |
F-11
aqueous layer turns a pale yellow (exact point is not too important here), add 3 drops of starch solution.
Then continue the titration until the aqueous layer and the CH2Cl2 layer become colorless at the same time.
If the aqueous layer becomes colorless and the CH2Cl2 layer is still colored, stop the titration and
swirl the flask vigorously, until I2 is transferred from the CH2Cl2 phase to the aqueous phase. If you do
not do this, you may overshoot the end point. Test the end point to be sure it is accurate. Read and record
the buret level (to 0.02 mL).
Dispose of the CH2Cl2 titrated solution in the special ORGANIC TOXIC WASTE container in
the fumehood.
Repeat the titration on a second sample. A third titration must be done if the results of the first two titrations
are not consistent. Again, to consider the results consistent for the titrations in this Part, the difference
between the ratios of
volume
titrant
volume
analyte
for the runs must be less than
0.015.
Dispose of the remaining CH2Cl2 in the ORGANIC TOXIC WASTE container provided in the fumehood
Have you remembered to record the concentration of the standardized sodium thiosulfate solution and the
initial concentration of KI in the aqueous triiodide solution?
When you have finished all of your titrations, and have disposed of all of the wastes
properly, wash your burets with hot tap water (four times) and rinse once with deionized
water. Leave them at your work station filled with deionized water.
Before leaving the laboratory, check to make sure that all of your equipment is clean, and back in your
drawer. As well, all communal equipment must be cleaned and returned to the designated location in the
laboratory. Remember to turn in the original copy of the Observations Sheet before leaving. The
second copy of the Observations Sheet should be kept in your laboratory manual for future reference.
