General Chemistry Principles, Patterns, and Applications, 2011

The reaction of mercury(II) acetate with sodium iodide. When colorless aqueous solutions of each
reactant are mixed, they produce a red precipitate, mercury(II) iodide, which is the result of an exchange reaction.
As you learned in Chapter 1 "Introduction to Chemistry", a solution is a homogeneous mixture in which substances
present in lesser amounts, called solutes, are dispersed uniformly throughout the substance in the greater amount,
the solvent. Anaqueous solution is a solution in which the solvent is water, whereas in anonaqueous solution, the
solvent is a substance other than water. Familiar examples of nonaqueous solvents are ethyl acetate, used in nail
polish removers, and turpentine, used to clean paint brushes. In this chapter, we focus on reactions that occur in
aqueous solution.
There are many reasons for carrying out reactions in solution. For a chemical reaction to occur, individual atoms,
molecules, or ions must collide, and collisions between two solids, which are not dispersed at the atomic, molecular,
or ionic level, do not occur at a significant rate. In addition, when the amount of a substance required for a reaction is
so small that it cannot be weighed accurately, using a solution of that substance, in which the solute is dispersed in a
much larger mass of solvent, enables chemists to measure its quantity with great precision. Chemists can also more
effectively control the amount of heat consumed or produced in a reaction when the reaction occurs in solution, and
sometimes the nature of the reaction itself can be controlled by the choice of solvent.
This chapter introduces techniques for preparing and analyzing aqueous solutions, for balancing equations that
describe reactions in solution, and for solving problems using solution stoichiometry. By the time you complete this
chapter, you will know enough about aqueous solutions to explain what causes acid rain, why acid rain is harmful,
and how a Breathalyzer measures alcohol levels. You will also understand the chemistry of photographic
development, be able to explain why rhubarb leaves are toxic, and learn about a possible chemical reason for the
decline and fall of the Roman Empire.
4.1 Aqueous Solutions
L E A R N I N G O B JE C T I V E
1. To understand how and why solutions form.
The solvent in aqueous solutions is water, which makes up about 70% of the mass of the human body and is essential
for life. Many of the chemical reactions that keep us alive depend on the interaction of water molecules with dissolved
compounds. Moreover, as we will discuss in Chapter 5 "Energy Changes in Chemical Reactions", the presence of large
amounts of water on Earth’s surface helps maintain its surface temperature in a range suitable for life. In this section,
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