Acids and Bases Chapter 16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Acids Have a _________ taste. Vinegar owes its taste to acetic acid. Citrus fruits contain citric acid. React with certain metals to produce ______________ gas. React with carbonates and bicarbonates to produce ______________ ______________ gas Have a __________ taste. Feel ________________. Many soaps contain bases. Bases 16.3

_________ acid is a substance that produces H + (H 3 O + ) in water _________ base is a substance that produces OH - in water 16.3

A __________________ acid is a proton donor A __________________ base is a proton acceptor acidbaseacidbase 16.1 acid conjugate base base conjugate acid

O H H+ O H H O H HH O H - + [] + Acid-Base Properties of Water H 2 O (l) H + (aq) + OH - (aq) H 2 O + H 2 O H 3 O + + OH - acid conjugate base base conjugate acid 16.2 __________________ of water

H 2 O (l) H + (aq) + OH - (aq) The Ion Product of Water K c = [H + ][OH - ] [H 2 O] [H 2 O] = constant K c [H 2 O] = K w = [H + ][OH - ] The __________________(K w ) is the product of the molar concentrations of H + and OH - ions at a particular _______________________. At 25 0 C K w = [H + ][OH - ] = __________ [H + ] = [OH - ] [H + ] > [OH - ] [H + ] < [OH - ] Solution Is 16.2

What is the concentration of OH - ions in an HCl solution whose hydrogen ion concentration is 1.3 M? K w = [H + ][OH - ] = _____________ [H + ] = _____________M [OH - ] = KwKw [H + ] == _____________ M 16.2

pH – A Measure of Acidity pH = _______________________ [H + ] = [OH - ] [H + ] > [OH - ] [H + ] < [OH - ] Solution Is neutral acidic basic [H + ] = 1 x [H + ] > 1 x [H + ] < 1 x pH At 25 0 C 16.3 pH[H + ] pH[H + ]

16.3 pOH = -log [OH - ] [H + ][OH - ] = K w = _____________ -log [H + ] – log [OH - ] = ________ pH + pOH = _____________ pHs of some common fluids

The pH of rainwater collected in a certain region of the northeastern United States on a particular day was What is the H + ion concentration of the rainwater? pH = - log [H + ] [H + ] = 10 -pH = = _____________ M antilog (pH) = -antilog (-log [H + ]) antilog = [H + ]

The OH - ion concentration of a blood sample is 2.5 x M. What is the pH of the blood? pH + pOH = _________ pOH = -log [OH - ]= -log (2.5 x )= _________ pH = – pOH = – 6.60 = _________ 16.3

Strong Electrolyte = __________________________ NaCl (s) Na + (aq) + Cl - (aq) H2OH2O Weak Electrolyte = __________________________ CH 3 COOH CH 3 COO - (aq) + H + (aq) Strong Acids are strong electrolytes HCl (aq) + H 2 O (l) H 3 O + (aq) + Cl - (aq) HNO 3 (aq) + H 2 O (l) H 3 O + (aq) + NO 3 - (aq) HClO 4 (aq) + H 2 O (l) H 3 O + (aq) + ClO 4 - (aq) H 2 SO4 (aq) + H 2 O (l) H 3 O + (aq) + HSO 4 - (aq) 16.4

HF (aq) + H 2 O (l) H 3 O + (aq) + F - (aq) Weak Acids are weak electrolytes HNO 2 (aq) + H 2 O (l) H 3 O + (aq) + NO 2 - (aq) HSO 4 - (aq) + H 2 O (l) H 3 O + (aq) + SO 4 2- (aq) H 2 O (l) + H 2 O (l) H 3 O + (aq) + OH - (aq) Strong Bases are strong electrolytes NaOH (s) Na + (aq) + OH - (aq) H2OH2O KOH (s) K + (aq) + OH - (aq) H2OH2O Ba(OH) 2 (s) Ba 2+ (aq) + 2OH - (aq) H2OH2O 16.4

F - (aq) + H 2 O (l) OH - (aq) + HF (aq) Weak Bases are weak electrolytes NO 2 - (aq) + H 2 O (l) OH - (aq) + HNO 2 (aq) Conjugate acid-base pairs: The conjugate base of a strong acid has no measurable strength. H 3 O + is the strongest acid that can exist in aqueous solution. The OH - ion is the strongest base that can exist in aqueous solution. 16.4

Relative Strengths of Conjugate Acid-Base Pairs

Strong AcidWeak Acid 16.4

What is the pH of a 2 x M HNO 3 solution? HNO 3 is __________________________. HNO 3 (aq) + H 2 O (l) H 3 O + (aq) + NO 3 - (aq) pH = -log [H + ] = -log [H 3 O + ] = -log(0.002) = _______ Start End M 0.0 M 16.4

What is the pH of a 1.8 x M Ba(OH) 2 solution? Ba(OH) 2 is a strong base – 100% dissociation. Ba(OH) 2 (s) Ba 2+ (aq) + 2OH - (aq) Start End M M0.0 M pH = – pOH = log(0.036) = _______ 16.4

HA (aq) + H 2 O (l) H 3 O + (aq) + A - (aq) Weak Acids (HA) and Acid Ionization Constants HA (aq) H + (aq) + A - (aq) K a = K a is the acid ionization constant KaKa weak acid strength 16.5

Ionization Constants of Some Weak Acids and Their Conjugate Bases at 25ºC

What is the pH of a 0.5 M HF solution (at 25 0 C)? HF (aq) H + (aq) + F - (aq) K a = [H + ][F - ] [HF] = 7.1 x HF (aq) H + (aq) + F - (aq) Initial (M) Change (M) Equilibrium (M) x-x+x+x +x+x K a = = __________ Ka  Ka  0.50 – x  0.50 K a << 1 x 2 = __________x = _______M [H + ] = [F - ] = M pH = -log [H + ] = _________ [HF] = 0.50 – x = 0.48 M 16.5

When can I use the approximation? 0.50 – x  0.50 K a << 1 When x is less than 5% of the value from which it is subtracted. x = M 0.50 M x 100% = 3.8% Less than 5% Approximation ok. What is the pH of a 0.05 M HF solution (at 25 0 C)? Ka  Ka  x2x = 7.1 x x = M M 0.05 M x 100% = 12% More than 5% Approximation not ok. Must solve for x exactly using quadratic equation or method of successive approximation. 16.5

Solving weak acid ionization problems: 1.Identify the major species that can affect the pH. In most cases, you can ignore the autoionization of water. Ignore [OH - ] because it is determined by [H + ]. 2.Use ICE to express the equilibrium concentrations in terms of single unknown x. 3.Write K a in terms of equilibrium concentrations. Solve for x by the approximate method. If approximation is not valid, solve for x exactly. 4.Calculate concentration of all species and/or pH of the solution. 16.5

What is the pH of a M monoprotic acid whose K a is 5.7 x ? HA (aq) H + (aq) + A - (aq) Initial (M) Change (M) Equilibrium (M) x-x+x+x +x+x K a = = __________ Ka  Ka  – x  K a << 1 x 2 = _________x = _______ M M M x 100% = 6.8% More than 5% Approximation not ok. 16.5

K a = x2x x = 5.7 x x x – 6.95 x = 0 ax 2 + bx + c =0 -b ± b 2 – 4ac  2a2a x = x = x = HA (aq) H + (aq) + A - (aq) Initial (M) Change (M) Equilibrium (M) x-x+x+x x x+x xx [H + ] = x = M pH = -log[H + ] =

percent ionization = Ionized acid concentration at equilibrium Initial concentration of acid x 100% For a monoprotic acid HA Percent ionization = [H + ] [HA] 0 x 100% [HA] 0 = initial concentration 16.5

NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) Weak Bases and Base Ionization Constants K b = [NH 4 + ][OH - ] [NH 3 ] K b is the base ionization constant KbKb weak base strength 16.6 Solve weak base problems like weak acids except solve for [OH-] instead of [H + ].

16.6 Ionization Constants of Some Weak Bases and Their Conjugate Bases at 25ºC

16.7 Ionization Constants of Conjugate Acid-Base Pairs HA (aq) H + (aq) + A - (aq) A - (aq) + H 2 O (l) OH - (aq) + HA (aq) KaKa KbKb H 2 O (l) H + (aq) + OH - (aq) KwKw K a K b = _____ Weak Acid and Its Conjugate Base Ka =Ka = KwKw KbKb Kb =Kb = KwKw KaKa

16.8 Ionization Constants of Some Diprotic Acids and a Polyprotic Acid and Their Conjugate Bases at 25ºC

Molecular Structure and Acid Strength H X H + + X - The stronger the bond The weaker the acid HF HCl HBr HI 16.9 Bond Energies for Hydrogen Halides and Acid Strengths for Hydrohalic Acids

Molecular Structure and Acid Strength Z O HZ O-O- + H + -- ++ The O-H bond will be more polar and easier to break if: Z is very electronegative or Z is in a high oxidation state 16.9

Molecular Structure and Acid Strength 1. Oxoacids having different central atoms (Z) that are from the same group and that have the same oxidation number. Acid strength increases with increasing electronegativity of Z H O Cl O O H O Br O O Cl is more electronegative than Br HClO 3 > HBrO

Molecular Structure and Acid Strength 2. Oxoacids having the same central atom (Z) but different numbers of attached groups. Acid strength increases as the oxidation number of Z increases. HClO 4 HClO 3 HClO 2 HClO 16.9

Acid-Base Properties of Salts Neutral Solutions: Salts containing an alkali metal or alkaline earth metal ion (except Be 2+ ) and the conjugate base of a strong acid (e.g. Cl -, Br -, and NO 3 - ). NaCl (s) Na + (aq) + Cl - (aq) H2OH2O Basic Solutions: Salts derived from a strong base and a weak acid. CH 3 COONa (s) Na + (aq) + CH 3 COO - (aq) H2OH2O CH 3 COO - (aq) + H 2 O (l) CH 3 COOH (aq) + OH - (aq) 16.10

Acid-Base Properties of Salts Acidic Solutions: Salts derived from a strong acid and a weak base. NH 4 Cl (s) NH 4 + (aq) + Cl - (aq) H2OH2O NH 4 + (aq) NH 3 (aq) + H + (aq) Salts with small, highly charged metal cations (e.g. Al 3+, Cr 3+, and Be 2+ ) and the conjugate base of a strong acid. Al(H 2 O) 6 (aq) Al(OH)(H 2 O) 5 (aq) + H + (aq)

Acid Hydrolysis of Al

Acid-Base Properties of Salts Solutions in which both the cation and the anion hydrolyze: K b for the anion > K a for the cation, solution will be ________ K b for the anion < K a for the cation, solution will be ________ K b for the anion  K a for the cation, solution will be ________ Acid-Base Properties of Salts

Oxides of the Representative Elements In Their Highest Oxidation States 16.11

_____________ is a substance that produces H + (H 3 O + ) in water A __________________ __________ is a proton donor A __________ is a substance that can accept a pair of electrons A __________ is a substance that can donate a pair of electrons Definition of An Acid H+H+ H O H + OH - acidbase N H H H H+H+ + N H H H H acidbase 16.12

Lewis Acids and Bases N H H H Which is the acid? Which is the base? F B F F + F F N H H H Are any protons donated or accepted? 16.12