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F-6
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5.
In a titration, 41.00 mL of 0.200 M thiosulfate solution was used to titrate 35.00 mL of iodine solution
in CH2Cl2. What is the molarity of the iodine solution?
Answer: 0.117 M
6.
Suppose that the total concentration of I
2(aq)
and I3
-
(aq)
in the aqueous layer was determined to be
0.0450 M. The [I
2(CH2Cl2)
] in dichloromethane was determined to be 0.0500 M.
(a)
What is [I
2(aq)
] in the aqueous layer?
Answer: 3.33 x 10
-4
M.
(b)
What is [I3
-
(aq)
] in the aqueous layer?
Answer: 0.0447 M.
(c)
If the concentration of iodide ion added at the beginning of the experiment was 0.225 M, what
is [I
-
(aq)
] at equilibrium?
Answer: 0.180 M
(d)
What value should be reported for K
eq
?
Answer: 746
REAGENTS AND EQUIPMENT
KI3 solution (0.01x moles of I2 added to 0.1xx M KI)
CH2Cl2 (dichloromethane)
0.11x M KI (potassium iodide)
1.0 M HCl (hydrochloric acid)
0.01xx M Na2S2O3 (standardized sodium thiosulfate)
two 50 mL burets
starch solution
EXPERIMENTAL PROCEDURE
I. Establishing Equilibria
Using the automatic dispenser, transfer 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.
