AP Chem Unit 13
Chapter 13 Equilibrium
Lab2
The solubility product is a special case of the equilibrium conditions in a saturated solution. In this experiment, you will work with solutions of lead(II) nitrate, Pb(NO3)2, and potassium iodide, KI, which will react to form a precipitate of lead(II) iodide, PbI2. The equilibrium reaction is:
PbI2(s) ↔ Pb+2(aq) + 2I-(aq)
The solubility product constant fro this reaction is expressed as follows:
Ksp = [Pb+2][I-]2
Notice that the term [PbI2] does not appear as a nominator for the solubility product constant. The concentration of the PbI2(s) is a constant, which depends upon the density of the crystals of solid lead iodide. Because the density does not change, you will use only the [Pb+2] and [I-], which will vary during the experiment.
Prepare the following data tables in your notebook:
A)
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Initial Volume of H2O |
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Final volume of H2O (after 100 drops of H2O |
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B)
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Trial |
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Equilibrium solution temperature |
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Drops of KI used |
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Molarity of KI |
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Pb(NO3)2 solution used |
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Molarity of Pb(NO3)2 |
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Obtain a clean 10-ml gradated cylinder, a clean dropper pipette, and a small beaker containing distilled water. Add about 1 ml of distilled water to the 10-ml graduated cylinder record the volume of water to the nearest 0.01 ml. Fill the dropper pipette with distilled water. Holding the dropper pipette vertically, slowly and carefully add 100 drops of distilled water to the 10-ml graduated cylinder. Keep the pipette vertical and squeeze slowly at all times for a consistent drop size. Record the final volume of water in the 10-ml graduated cylinder to the nearest 0.01 ml after 100 drops have been added. Repeat the process two more times.
Measure 10.0 ml of 0.25 M Pb(NO3)2 solution in a graduated cylinder. Pour the solution in a 50-ml Erlenmeyer flask. Place the flask against a black background. Add 0.10 M KI solution from the dropper pipette a drop at a time, counting the drops. Swirl the flask after adding each drop to promote the dissolving of the yellow PbI2 precipitate formed. When a faint yellow color of PbI2(s) persists, you have just reached the ENDPOINT of the titration and equilibrium has been established. Record the number of drops of KI solution used.
Record the temperature of the equilibrium mixture to the nearest 0.2˚C.
Repeat the drop-by-drop titration procedure with other Pb(NO3)2 and KI solutions as specified in the data table. If time is limited , your instructor may assign certain titrations to each person and ask you to exchange data at the end of the laboratory period.
A)
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Trial |
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Volume of 100 drops |
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Volume of 1.00 drop |
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ml 1 |
B)
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Trial |
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Liters of KI used |
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Molarity of KI |
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Moles of KI used |
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Liters of Pb(NO3)2 used |
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Molarity of Pb(NO3)2 |
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Moles of Pb(NO3)2 used |
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Total volume of equilibrium solution (liters) |
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[I-] |
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[Pb+2] |
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Ksp |
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