In this qualitative analysis
applet there are four bottles labeled A, B, C,
and D. All contain colorless solutions. The first
part of the lab is to mix the reagents one after
another in a certain order to produce an colorful
sequence: the colorless solutions turn yellow
when two are mixed, blue when a third solution is
added, and back to colorless when the fourth
solution is added. The second part of the lab is
to identify the contents of each bottle. Each
bottle contains one of the following reagents:
potassium iodide (KI), sodium thiosulfate (Na2S2O3),
hydrogen peroxide (H2O2),
and soluble starch. Here are some hints:
| 1.
Iodine (I2), in the presence
of iodide at these concentrations, will
appear yellow. |
| 2.
Starch makes a blue complex with iodine
(I2). |
| 3.
Hydrogen peroxide is an oxidizing agent.
It could, for example, oxidize iodide (I-)
to iodine (I2). |
| 4.
Sodium thiosulfate is a reducing agent.
It could reduce iodine (I2) to
iodide (I-). |
Exercise.
First use the applet to determine the order of
addition so that you can produce the
colorless-yellow-blue-colorless pattern. Then
devise a procedure that will always allow you to
identify which reagent is in which bottle.
When
using the Lab Bench, drag the droppers to the
test tubes to add reagents. A tube will become
red when it is ready to receive reagent. Test
tubes can be dragged to the waste can to empty
them.
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