Determining the Ksp of Calcium Hydroxide

Figure from experiment 23 from Advanced Chemistry with Vernier

Introduction

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.

{\text{Ca(OH}}{{\text{)}}_{\text{2}}}{\text{ }}(s) \leftrightarrow {\text{C}}{{\text{a}}^{{\text{2  +  }}}}{\text{ (aq)   +   2O}}{{\text{H}}^{{\text{  -  }}}}{\text{(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.

{K_{sp}} = [{\text{C}}{{\text{a}}^{{\text{2 + }}}}{\text{][O}}{{\text{H}}^{\text{ - }}}{]^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.
  • Calculate the Ksp of Ca(OH)2.

Sensors and Equipment

This experiment requires each of the following Vernier sensors and equipment (unless otherwise noted):

Additional Requirements

You may also need an interface and software for data collection. What do I need for data collection?

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The student-version preview includes:

  • Step-by-step instructions for computer-based data collection
  • List of materials and equipment

Note: The experiment preview of the computer edition does not include essential teacher information, safety tips, or sample data. Instructions for Logger Pro and other software (such as LabQuest App or TI handheld software, where available) are on the CD that accompanies the book. We strongly recommend that you purchase the book before performing experiments.

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Experiment 23 from Advanced Chemistry with Vernier Lab Book

<i>Advanced Chemistry with Vernier</i> book cover

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