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Equilibria of Other Reaction Classes

Introduction

OpenStaxCollege

Learning Objectives

  • Precipitation and Dissolution
  • Lewis Acids and Bases
  • Multiple Equilibria
The mineral fluorite (CaF2) is deposited through a precipitation process. Note that pure fluorite is colorless, and that the color in this sample is due to the presence of other metals in the crystal.


An image is shown of a cluster of clear crystals, showing primarily cubic and some octahedral shapes. A large cubic crystal at the center of the photograph has a deep emerald green center with deep purple corners and a small royal blue region just right of center. A smaller cubic crystal to its left shows purple corners and edges with royal blue coloration toward the center. Similar coloration is seen in other crystals in the structure, though most of the smaller crystals are clear and colorless.

In [link], we see a close-up image of the mineral fluorite, which is commonly used as a semiprecious stone in many types of jewelry because of its striking appearance. These solid deposits of fluorite are formed through a process called hydrothermal precipitation. In this process, the fluorite remains dissolved in solution, usually in hot water heated by volcanic activity deep below the earth, until conditions arise that allow the mineral to come out of solution and form a deposit. These deposit-forming conditions can include a change in temperature of the solution, availability of new locations to form a deposit such as a rock crevice, contact between the solution and a reactive substance such as certain types of rock, or a combination of any of these factors.

We previously learned about aqueous solutions and their importance, as well as about solubility rules. While this gives us a picture of solubility, that picture is not complete if we look at the rules alone. Solubility equilibrium, which we will explore in this chapter, is a more complex topic that allows us to determine the extent to which a slightly soluble ionic solid will dissolve, and the conditions under which precipitation (such as the fluorite deposit in [link]) will occur.

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