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General Chemistry Principles, Patterns, and Applications, 2011

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that kind of prediction is to attempt to place the reaction into one of several familiar classifications,<br />

refinements of the five general kinds of reactions introduced in Chapter 3 "Chemical Reactions" (acid–<br />

base, exchange, condensation, cleavage, <strong>and</strong> oxidation–reduction reactions). In the sections that follow,<br />

we discuss three of the most important kinds of reactions that occur in aqueous solutions: precipitation<br />

reactions (also known as exchange reactions), acid–base reactions, <strong>and</strong> oxidation–reduction reactions.<br />

Summary<br />

The chemical equation for a reaction in solution can be written in three ways. Theoverall chemical<br />

equation shows all the substances present in their undissociated forms; the complete ionic<br />

equation shows all the substances present in the form in which they actually exist in solution; <strong>and</strong><br />

the net ionic equation is derived from the complete ionic equation by omitting all spectator ions,<br />

ions that occur on both sides of the equation with the same coefficients. Net ionic equations demonstrate<br />

that many different combinations of reactants can give the same net chemical reaction.<br />

K E Y T A K E A W A Y<br />

<br />

A complete ionic equation consists of the net ionic equation <strong>and</strong> spectator ions.<br />

C O N C E PTUAL P R OBLEM<br />

1. What information can be obtained from a complete ionic equation that cannot be obtained from the overall<br />

chemical equation?<br />

4.5 Precipitation Reactions<br />

LEARNING OBJECTIVE<br />

1. To identify a precipitation reaction <strong>and</strong> predict solubilities.<br />

A precipitation reaction is a reaction that yields an insoluble product—aprecipitate—when two solutions are<br />

mixed. In Section 4.4 "Ionic Equations", we described a precipitation reaction in which a colorless solution of silver<br />

nitrate was mixed with a yellow-orange solution of potassium dichromate to give a reddish precipitate of silver<br />

dichromate:<br />

Equation 4.15<br />

AgNO3(aq) + K2Cr2O7(aq) → Ag2Cr2O7(s) + KNO3(aq)<br />

This equation has the general form of an exchange reaction:<br />

Equation 4.16<br />

AC + BD → AD insoluble + BC<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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