Acid-Base Equilibrium Chapter 18

Acids and Bases Arrhenius acids: generate H+ in water bases: generate OH- in water Brønsted-Lowry acids: H+ donors bases: H+ acceptors HCl + H2O  Cl + H3O+ acid base

H3O+ = H+(aq) = proton in water

Conjugate acid-base pairs Conjugate base: remains after H+ is lost acid: HCl conj. base: Cl- Conjugate acid: remains after H+ is gained base: NH3 conj. acid: NH4+ Conjugate Pair Acid Base + Base Acid + Conjugate Pair

Strong and Weak Acids Strong: 100% dissociation good H+ donor equilibrium lies far to right (HNO3) generates weak base (NO3-) Weak: <100% dissociation not-as-good H+ donor equilibrium lies far to left (CH3COOH) generates strong base (CH3COO-)

Relative Acid Strength Relative Conj. Base Strength Very strong Very weak Strong Weak Weak Strong Very weak Very strong

Acid Dissociation Constant

Strength vs. Ka Ka Increases

Water is amphoteric Acid Base Conj. Acid Conj. Base

Proton Transfer in Water H + -

[H3O+] and [OH-] [H3O+] 1x100 to 1x10-14 in water [OH-] 1x10-14 to 1x100 in water

Finding [H3O+] and [OH-]

pH Scale pH 0 to 14 in water pOH 14 to 0 in water pKw = pH + pOH = 14

H+ OH- pH and pOH As [H3O+] rises, [OH-] falls As pH falls, pOH rises 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Acidic Neutral Basic As pH falls, pOH rises

Indicators

Polyprotic Acids 1. H3PO4 H2PO4- + H+ Ka1 = 7.2 x 10-3 3. HPO42- PO43- + H+ Ka3 = 4.2 x 10-13 Ka1 > Ka2 > Ka3

Strength of Bases Strong: 100% dissociation OH- supplied to solution NaOH(s)  Na+(aq) + OH-(aq) Weak: <100% dissociation OH- by reaction with water CH3NH2(aq) + H2O(l) CH3NH2(aq) + OH-(aq)

Base Dissociation Constant

Kw, Ka and Kb

Structure and Acid-Base Behavior Binary hydrides: 1. Bond polarity (high  acid strength) 2. Bond strength (low  acid strength)

Structure and Acid-Base Behavior Binary oxides: 1. Acidic oxides (acid anhydrides) O—X bond: strong and polar SO2, SO3, NO2, P4O10, … 2. Basic oxides (basic anhydrides) O—X bond: ionic K2O, CaO, …

Structure and Acid-Base Behavior Oxoacids (HaXbOc): 1. Same number of O on different X EN of X 2. Different number of O on same X more O

Relative Strengths of Oxoacids

Increasing Acid Strength Cl O H 1 O Electron density O Cl O H 2 O Electron density O Cl O H O 3 O Electron density O O Cl O H 4 O O Electron density Increasing Acid Strength

Lewis Acids and Bases Lewis Acid: electron pair acceptor Lewis Base: electron pair donor A l 3 + 6 H O Acid Base