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F-9
EXPERIMENTAL PROCEDURE
Please put on your safety glasses.
I. Establishing Equilibria
Using the automatic dispenser, dispense 75 mL of KI3 solution,(I
-
(aq)
, I
2(aq)
, I3
-
(aq)
), from the stock bottle into a
300 mL Erlenmeyer flask. This solution has been prepared by the addition of a measured quantity of iodine
to a solution of an accurately known concentration of KI (0.1xx M). Record on your Observations Sheet
the initial KI concentration written on the bottle.
Add 40.0 mL of dichloromethane to the flask and stopper it with a cork stopper.
CAUTION: AVOID BREATHING CH2Cl2. DO NOT LEAVE CH2Cl2 ON YOUR DESK
UNCOVERED.
Swirl the flask for fifteen minutes, taking care not to splash the solution on the cork stopper. Pour the
contents of the flask into a dry 100 mL graduated cylinder and allow
10 minutes for the two liquids to separate. As indicated in Figure 1, the aqueous (top) layer contains I
2(aq)
,
I3
-
(aq)
,
and I
-
(aq)
, while the CH2Cl2 (bottom) layer contains only I
2(CH2Cl2)
.
II. Titration of the Aqueous Layer.
Clean a buret, then rinse it with 8.0 mL of the aqueous layer from Part I. Fill the buret with the aqueous
layer, being careful not to transfer any of the organic layer. If some CH2Cl2 does go into the buret, allow it
to settle to the bottom of the buret and then drain it from the bottom of the buret back into the graduated
cylinder. In this experiment the meniscus is difficult to read because the liquid is colored. You may read the
top of the meniscus or any fixed point that is more convenient. Deliver about 15 mL, accurately measured,
of the aqueous layer from this buret into a clean (but not necessarily dry) 125 mL Erlenmeyer flask. Record
the initial and final readings on the buret (reminder: all buret readings must be made to 0.02 mL or
marks will be deducted). Add 2.0 mL of 1.0 M HCl solution to the flask.
NOTE: The HCl does not participate in the reaction but prevents conversion of I
2(aq)
to IO3
-
(aq)
, which
occurs in basic solutions.
Clean a second buret, then rinse it with 8.0 mL of the standardized sodium thiosulfate (Na2S2O3) solution.
