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Determining the Ksp
of Calcium Hydroxide
Calcium hydroxide is an ionic solid that is sparingly soluble in water. A saturated, aqueous, solution of Ca(OH)2 is represented in equation form as shown below. Ca(OH)2 (s) ↔ Ca2+ (aq) + 2OH– (aq)

The solubility product expression describes, in mathematical terms, the equilibrium that is established between the solid substance and its dissolved ions in an aqueous system. The equilibrium expression for calcium hydroxide is shown below. Ksp = [Ca2+][OH–]2

The constant that illustrates a substance’s solubility in water is called the Ksp. All compounds, even the highly soluble sodium chloride, have a Ksp. However, the Ksp of a compound is commonly considered only in cases where the compound is very slightly soluble and the amount of dissolved ions is not simple to measure. Your primary objective in this experiment is to test a saturated solution of calcium hydroxide and use your observations and measurements to calculate the Ksp of the compound. You will do this by titrating the prepared Ca(OH)2 solution with a standard hydrochloric acid solution. By determining the molar concentration of dissolved hydroxide ions in the saturated Ca(OH)2 solution, you will have the necessary information to calculate the Ksp. OBJECTIVES

In this experiment, you will
Titrate a saturated Ca(OH)2 solution with a standard HCl solution. Determine the [OH–] for the saturated Ca(OH)2 solution.
Calculate the Ksp of Ca(OH)2.

Figure 1

MATERIALS
LabQuest| saturated calcium hydroxide, Ca(OH)2, solution| LabQuest App| 0.050 M hydrochloric acid, HCl, solution|
Vernier pH Sensor| (optional) indicator solution|
50 mL buret| buret clamp|
two 100 mL beakers| filter paper|
two 250 mL beakers| filter funnel|
two 50 mL graduated cylinders| magnetic stirrer and stirring barthumb drive for storing data| ring stand and ring| |
PROCEDURE
1.Obtain and wear goggles.
2.Obtain about 70 mL of a saturated calcium hydroxide...
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