Chapter 1611 Chapter 16 Acid-Base Equilibria CHEMISTRY The Central Science 9th Edition

Chapter 1621 Acids: taste sour cause dyes to change color Bases: taste bitter feel soapy Arrhenius: acids increase [H + ], bases increase [OH - ] in AQUEOUS solution Arrhenius: acid + base  salt + water Problem: the definition confines us to aqueous solutions 16.1: Acids and Bases: A Brief Review

Chapter 1631 The H + Ion in Water The H + (aq) ion is a proton with no electrons In water, the H + (aq) form clusters The simplest cluster is H 3 O + (aq) A hydrated proton Larger clusters are H 5 O 2 + and H 9 O 4 + Generally H + (aq) and H 3 O + (aq) are used interchangeably 16.2: Brønstead-Lowry Acids and Bases

Chapter 1641 Proton Transfer Reactions Brønsted-Lowry theory: Acid donates H + and base accepts H + Brønsted-Lowry base does not need to contain OH - HCl(aq) + H 2 O(l)  H 3 O + (aq) + Cl - (aq) –HCl donates a proton to water (HCl is an acid) –H 2 O accepts a proton from HCl (H 2 O is a base) Water can behave as either an acid or a base Amphoteric substances can behave as acids and bases With a stronger base, it is an acid (and vice versa)

Chapter 1651 Conjugate Acid-Base Pairs Whatever is left of the acid after the proton is donated is called its conjugate base Whatever remains of the base after it accepts a proton is called a conjugate acid –After HA (acid) loses its proton it is converted into A - (base) –HA and A - are conjugate acid-base pairs –After H 2 O (base) gains a proton it is converted into H 3 O + (acid) –H 2 O and H 3 O + are conjugate acid-base pairs Conjugate acid-base pairs differ by only one proton

Chapter 1661 Relative Strengths of Acids and Bases The stronger the acid, the weaker the conjugate base Text, P. 618

Chapter 1671 Generalizations about Acid and Base Behavior 1.Strong acids completely transfer their protons to water The conjugate base of a strong acid has negligible acid-base properties The conjugate acid of a strong base has negligible acid-base properties 2.Weak acids partly dissociate in aqueous solution The conjugate bases of weak acids are weak bases 3.Substances with negligible acidity (CH 4 ) contain H but don’t behave as acids in water Their conjugate bases are strong bases (form (OH) - in water)

Chapter 1681 Proton Transfer Reactions Strong acids and bases react with water to liberate H + (aq) and (OH) - (aq) ions The leveling effect of water: one can’t distinguish among the strengths of the strong acids or strong bases Place HCl, HBr or HI in dilute acetic acid and there is a noticeable difference in their strengths H + is the strongest acid that can exist in equilibrium in aqueous solution OH - is the strongest base that can exist in equilibrium in aqueous solution

Chapter 1691 Proton Transfer Reactions In acid-base reactions, the equilibrium favors transfer of the proton from the stronger acid to the stronger base Strong acid in water: Equilibrium favors the right side HSO 4 - (aq) + CO 3 -2 (aq) SO 4 -2 (aq) + HCO 3 - (aq) Compare bases: CO 3 -2 is from HCO 3 - SO 4 -2 is from HSO 4 - Use chart ( P. 618) to determine which base is stronger (CO 3 -2 ) The stronger base and acid are consumed Proton is transferred to the stronger base Production of the weaker electrolytes is favored

Chapter The reaction favors the consumption of the stronger acid and stronger base and the formation of the weaker acid and weaker base (the weaker electrolytes)

Chapter Proton Transfer Reactions Weak acid in water: Equilibrium favors the left side The anion of the acid is a stronger base, so it accepts a proton from the H 3 O + HC 2 H 3 O 2(aq) + H 2 O (l) H 3 O + (aq) + C 2 H 3 O 2 - (aq) Use chart ( P. 618) to determine which base is stronger (C 2 H 3 O 2 - ) The stronger base and acid are consumed Proton is transferred to the stronger base

Chapter The reaction favors the consumption of the stronger acid and stronger base and the formation of the weaker acid and weaker base (the weaker electrolytes) Complete Sample Problems: # 5, 7, 9, 11, 15