Chemistry Outcomes Review: Chapter 6

Chemical Reactions

We have divided chemical reactions into three large classes: precipitation reactions, Lewis acid-base reactions, and oxidation-reduction reactions. In precipitation reactions, ions lose their bonding to waters of hydration and form crystals held together by attractions between cations and anions. The electrons on the cations and anions remain with the same atomic core throughout the reaction.

In Lewis acid-base reactions, a nonbonding electron pair on a Lewis base is attracted to a positive center on a Lewis acid and the electrons form a new covalent bond between the two reactants. Bronsted-Lowry acid-base reactions are a special class of Lewis acid-base reactions in which the new covalent bond is to a proton. We showed how to account for and predict the relative strengths of these acids and bases. Lewis acid-base reactions also occur between ligands, Lewis bases, and metal ions, Lewis acids, to which the bases bond to form metal ion complexes, many of which are important in biological systems. Finally Lewis acid-base reactions occur between nucleophiles, Lewis bases, and electrophiles, Lewis acids, to form a variety of final products from the rearrangements that occur after the initial bond formation. The examples we chose were condensation reactions, many of which are used by both man and nature to create polymers.

Oxidation-reduction reactions involve complete transfer of one or more electrons from one reactant to another. The reactant that loses electrons is oxidized and the reactant that gains electrons is reduced. Oxidation numbers identify oxidation-reduction reactions and can be used to balance their reaction equations. Another method for balancing is to break the reaction into half reactions, a reduction and an oxidation, balance these separately, and then recombine them.

Check you understanding of the ideas in the chapter by reviewing these expected outcomes of your study.

You should be able to:

• Classify a chemical change as a precipitation, Lewis acid-base, or oxidation-reduction reaction based on known reactants and products, or from experimental observations on the change [Sections 6.2, 6.4, 6.6, 6.7, 6.9, and 6.11].
• Predict probable precipitation reactions based on the cation and anion charges [Section 6.2].
• Use the stoichiometry of continuous variations studies to determine the formula of a reaction product or the ratio in which reactants react [Section 6.2].
• Define and give examples of three classes of Lewis acid-base reactions: Bronsted-Lowry proton transfers, metal ion complexation, and nucleophile-electrophile reactions [Sections 6.3, 6.4, 6.6, and 6.7].
• Use the observed pH and stoichiometry of a solution to determine the relative basicity (acidity) of the species in the solution [Section 6.4].
• Predict the relative basicities (acidities) of a series of Lewis/Bronsted-Lowry bases (acids) of known structure [Section 6.5].
• Use relative basicities (acidities) to predict the predominant species in solutions of Lewis/Bronsted-Lowry bases (acids) [Sections 6.4 and 6.5].
• Recognize the formation of a metal ion complex between a Lewis base and a metal ion in solution by observations on mixtures of the reactants (or in competitions between the Lewis base and another reactant for the metal ion) and suggest a structure for the complex [Section 6.6].
• Identify the nucleophilic and electrophilic sites in a pair of reactants that react to form a condensation product, including condensation polymers [Section 6.7]
• Predict the product of a nucleophile-electrophile reaction, including condensation polymerization, between reactants with the functional groups we have introduced [Sections 6.7 and 6.8].
• Use formal charge to explain the rearrangements that some reaction intermediates undergo or to explain the relative stability of different isomeric Lewis structures [Section 6.8].
• Identify the molecules or ions that are reduced and oxidized and their respective products in an oxidation-reduction reaction [Sections 6.9, 6.10, and 6.11].
• Assign oxidation numbers to all the atoms in a given molecule or ion [Sections 6.9 and 6.11].
• Balance a given oxidation-reduction reaction in acidic or basic solution by inspection, the oxidation-number method, or the half-reactions method [Sections 6.9, 6.10, and 6.11].
• Use your knowledge of the oxidation numbers of atoms in various molecules or ions to predict possible reduced or oxidized products from a reaction [Sections 6.10 and 6.11].
• Use oxidation numbers to show that a given reaction is an internal oxidation-reduction [Section 6.11].