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. An aqueous solution is a solution in which the solvent is water, whereas in a nonaqueous 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: General Properties of Aqueous Solutions
- Aqueous solutions can be classified as polar or nonpolar depending on how well they conduct electricity. Most chemical reactions are carried out in solutions, which are homogeneous mixtures of two or more substances. In a solution, a solute (the substance present in the lesser amount) is dispersed in a solvent (the substance present in the greater amount). Aqueous solutions contain water as the solvent, whereas nonaqueous solutions have solvents other than water.
- 4.2: Precipitation Reactions
- A complete ionic equation consists of the net ionic equation and spectator ions. Predicting the solubility of ionic compounds gives insight into feasibility of reactions occuring. The chemical equation for a reaction in solution can be written in three ways. The overall chemical equation shows all the substances in their undissociated forms; the complete ionic equation shows substances in the form in which they actually exist in solution; and the net ionic equation omits all spectator ions.
- 4.3: Acid-Base Reactions
- An acidic solution and a basic solution react together in a neutralization reaction that also forms a salt. Acid–base reactions require both an acid and a base. In Brønsted–Lowry terms, an acid is a substance that can donate a proton and a base is a substance that can accept a proton. Acids also differ in their tendency to donate a proton, a measure of their acid strength. The acidity or basicity of an aqueous solution is described quantitatively using the pH scale.
- 4.4: Oxidation-Reduction Reactions
- Oxidation–reduction reactions are balanced by separating the overall chemical equation into an oxidation equation and a reduction equation. In oxidation–reduction reactions, electrons are transferred from one substance or atom to another. We can balance oxidation–reduction reactions in solution using the oxidation state method, in which the overall reaction is separated into an oxidation equation and a reduction equation. The outcome of these reactions can be predicted using the activity series.
- 4.5: Concentration of Solutions
- Solution concentrations are typically expressed as molarities and can be prepared by dissolving a known mass of solute in a solvent or diluting a stock solution. The concentration of a substance is the quantity of solute present in a given quantity of solution. Concentrations are usually expressed in terms of molarity, defined as the number of moles of solute in 1 L of solution.
- 4.6: Solution Stoichiometry and Chemical Analysis
- The topic solution stoichiometry deals with quantities in chemical reactions taking place in solutions. Quantitative analysis of an unknown solution can be achieved using titration methods. In a titration, a measured volume of a solution of one substance, the titrant, is added to a solution of another substance to determine its concentration. The equivalence point in a titration is the point at which exactly enough reactant has been added for the reaction to go to completion.
- 4.7: Reactions in Aqueous Solution (Exercises)
- These are homework exercises to accompany the Textmap created for "Chemistry: The Central Science" by Brown et al.
- 4.8: Reactions in Aqueous Solution (Summary)
- This is the summary Module for the chapter "Reactions in Aqueous Solution" in the Brown et al. General Chemistry Textmap.