chm1046 Exam 3 Study Guide

# chm1046 Exam 3 Study Guide - CHM 1046 16 Study Guide...

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CHM 1046: Chapters 14, 15 & 16 Study Guide Chapter 14: Acids and Bases: This chapter is concerned with a particular type of equilibrium, the behavior of acids and bases, and introduces the pH scale as a way of simplifying these equilibrium calculations. The Nature of Acids and Bases: Know the Arrhenius and Bronsted-Lowry definitions of acids and bases Write the reaction of an acid or base with water Identify the acid, base, conjugate acid, and conjugate base in a reaction Write the expression for the acid dissociation constant (K a ) for a reaction o Understand that K a is just an equilibrium expression specific to an acid equilibrium ± Therefore, K a is constant ± The position of equilibrium (i.e. [H + ]) is variable Acid Strength: Know which acids and bases are strong Know the relationship between the strength of an acid and its conjugate base (and vice versa) Define amphoteric Know the ion-product constant for water: o K w = [H + ][OH - ] = 1.00 x 10 -14 at 25 o C o [H + ] = [OH - ] = 1.00 x 10 -7 M at 25 o C o [H + ] = [OH - ] in water at any temperature, but K w varies with temperature Calculate [H + ] if given [OH - ], and vice versa pH Scale: pH = -log[H + ] pOH = -log[OH - ] pH + pOH = 14.00 pH of Strong acids: Strong acids dissociate completely in water o pH can be calculated from the concentration of the strong acid directly ± a very dilute solution of a strong acid is the exception. If the concentration of the acid is less than 1 x 10 -7 M, then pH = 7 from the autoionization of water pH of Weak Acids: Treat the reaction as an equilibrium problem o Determine the initial concentrations o Determine x, the change in concentration of the reactants and products o Plug x into the K a expression and solve ± Use the approximation that x is small in comparison to the initial concentrations. o x = [H + ] pH = -log[H + ]

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In a mixture of weak acids, the acid with the largest K a will dominate the equilibrium Bases: Solve base problems the same way as the acid problems: o Strong bases are completely dissociated, so pOH = -log[OH - ] o Weak bases are equilibrium problems ± K a = (1.00x10 -14 )/K b Polyprotic Acids: Polyprotic acids have more than one acidic hydrogen o Therefore, they have more than one K a value, for the stepwise dissociation of each acidic proton Since K a1 >>K a2 , neglect the second dissociation, and solve for pH with just K a1 Acid-Base Properties of Salts: An ionic compound that contains the anion of a weak acid will be a weak base o Example: C 2 H 3 O 2 - comes from acetic acid (C 2 H 3 O 2 H). It is the conjugate base of a weak acid, so it is itself a weak base An ionic compound that contains the cation of a weak base will be a weak acid o Example: NH 4 + comes from ammonia (NH 3 ). It is the conjugate acid of a weak base, so it is itself a weak acid. Effect of Structure on Acid-Base Properties:
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## This note was uploaded on 04/04/2011 for the course CHM 1046 taught by Professor Wolfe,d during the Spring '08 term at Hillsborough.

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chm1046 Exam 3 Study Guide - CHM 1046 16 Study Guide...

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