CH. 16 ACID -- BASE 16.4 pH scale (pOH) 16.1 Definition 16.2 Bronstad-Lowry Conjugate Pairs Strength Leveling Effect 16.3 Dissociation of water Kw 16.5 Strong Acid Strong Base pH & [ ] 16.6 Weak Acids Ka & pH % Ionization Polyprotic Acids 16.7 Weak Bases Kb & pH Acid Base Yields 16.9 Salt Solutions Anions/Cations Lewis 16.8 Ka & Kb Relation 16.10 Binary Acids Oxyacids Carboxylic Acids 16.11 Bronstad-Lowry

ACID BASE CHEMISTRY TERMS, ETC. AMPHOTERIC: Subst. acts as either an acid or a base Proton (Acidic p+): H+ ion; the acidic hydrogen(s) present in an acid HNO3: one H+ H2SO4: two H+ H3PO4: three H+ MONOPROTIC ACID: An acid w/ one H+ DIPROTIC ACID: An acid w/ two H+ POLYPROTIC ACID: An acid w/ 3 or more H+

TERMS, ETC. ACID: Subst. in H2O incr [H+] BASE: Subst. in H2O incr [OH-] Effects H+ Ion in H2O HYDRONIUM ION: H2O (l) + H+1 (aq) ---------> H3O+1 (aq)

BRONSTAD-LOWRY ACID: Subst. that donate acidic proton, H+ Proton donor HCl(g) + H2O(l) ----> H3O+(aq) + Cl-(aq) BASE: Subst. that gains acidic proton, H+ Proton acceptor

Figure 16-02-01UN Title: Brønsted–Lowry acids and bases. Caption: Because the emphasis in the Brønsted–Lowry concept is on proton transfer, the concept also applies to reactions that do not occur in aqueous solution. In the reaction between HCl and NH3, for example, a proton is transferred from the acid HCl to the base NH3. Notes: Keywords:

CONJUGATE ACID-BASE PAIRS Acid, loses H+, form conjugate base Base, gains H+, forms conjugate acid acid1 base2 base1 acid2 CONJUGATE ACID-BASE PAIRS

Fig 16.3 pg. 657 Figure 16-04 Title: Relative strengths of some conjugate acid–base pairs. Caption: The two members of each pair are listed opposite each other in the two columns. The acids decrease in strength from top to bottom, whereas their conjugate bases increase in strength from top to bottom. Notes: Keywords:

RELATIVE STRENGTH HX(aq) + H2O(l) ----> H3O+(aq) + X-(aq) H2O stronger base than X- X weaker base --- equilib + acid ion of weak acid react w/ H2O, produces H3O+ Strong Acid + Weak Base --- Acidic HCl(g) + H2O(l) ----> H3O+(aq) + Cl-(aq) H2O stronger base than Cl-

X- stronger base than H2O X stronger base <---- equilib Weak Acid + Strong Base --- Basic CH3COOH(aq) + H2O(l) ----> H3O+(aq) + CH3COO-(aq) CH3COO- stronger base than H2O Proton Transfer: ability of 2 bases attract protons

AUTOIONIZATION OF WATER Kc[H2O]2 = Kw = [H3O+][OH-] = 1.0*10-14 Solution Acid [H3O+] > [OH-] Neutral [H3O+] = [OH-] Basic [OH-] > [H3O+]

Kw: constant for water, 1*10-14 Kw = [H+][OH-] 1*10-14 = [H+][OH-] pH SCALE NEUTRAL ( ) MILD ACIDIC MILD BASIC 7 14 WEAK ACIDIC WEAK BASIC STRONG ACIDIC STRONG BASIC Kw: constant for water, 1*10-14 Kw = [H+][OH-] 1*10-14 = [H+][OH-] pKw = -Log [H2O] = -Log [1*10-14] = -Log [10-14] -Log [1] = -(-14) - 0 = 14 pKw = pH + pOH pH = -Log [H+] pOH = -Log [OH-] [H+] = 1*10-pH [OH-] = 1*10-pOH Log 10exp = exp log 106 = 6 Log 10-4 = -4 Log 1 = 0

Fig. 16.5 pg 663 Figure 16-05 Title: H+ concentrations and pH values of some common substances at 25 oC. Caption: The pH of a solution can be estimated using the benchmark concentrations of H+ and OH– corresponding to whole-number pH values. Notes: Keywords:

pH -- pOH -- [H+] -- [OH-] CALCULATIONS Formulas to Use Constants Kw = 1 *10 –14 pKw = 14 pH = -log [H+] pOH = -log [OH-] Rules for LOGS [H+] = 1*10-pH Log 1 = 0 [OH-] = 1*10-pOH Log 10exp = exponent

Rules for LOGS Log 1 = 0 Log 103.17 = 3.17 Log 10exp = exponent

Calculate pH for the following solutions 1) [H+] = 1 * 10-9 pH = -log (1*10-9) = -(-9) = 9 2) [H+] = 0.001 0.001 = 1*10-3 pH = -log (1*10-3) = -(-3) = 3

Find pH & pOH 3) [H+] = 3.6 * 10-2 pH = -log(3.6*10-2) = 1.44 = 2 – 0.56 = 1.44 -log 10-2 = 2 OR pKw = pH + pOH 14 = 1.44 + pOH pOH = 14 – 1.44 = 12.56 pOH OR = 2.78*10-13 pOH = 13 – log 2.78 = 13 – 0.44 =

If [H+] is 6.7*10-9 mol/L, what is the pH? ACIDIC, BASIC, NEUTRAL What is the [OH-]? What is the pOH? Find pH Find pOH pH = -log(6.7*10-9) = 9 – log 6.7 = 9 – 0.83 = 8.17 pOH = 14 – 8.17 = 5.83 Find [OH-] BASIC [OH-] = 1*10-5.83 OR [OH-] = 1*10-14 6.7*10-9 = 1.49*10-6

TITRATIONS Strong Acid + Strong Base ------ Neutral +/- ions of acid not react w/ H2O Strong Acid + Weak Base --- Acidic + acid ion weak acid react w/ H2O, produces H3O+ HBr + NH4OH NH4 is a weak acid reacts w/ H2O to produce H3O+ Weak Acid + Strong Base --- Basic acid ion weak base produces OH- HCN: CN- is weak base reacts w/ H2O to produce OH- Weak Acid + Weak Base ---- ??????? Both +/- ions react w/ H2O

DISSOCIATION HA: acid A-: anion Ka: acid-dissociation constant Strong Acid -- SA HA(aq) + H2O(l) --------> H3O+(aq) + A-(aq) SA in solution; no HA present, most all H3O+ @ equilibrium Qc = Kc >>>> 1 Weak Acid -- WA HCN(aq) + H2O(l) --------> H3O+(aq) + CN-(aq) WA in solution; no H3O+ present, most all HA @ equilibrium Qc = Kc <<<< 1 Stronger Acid ==> higher [H3O+] ===> larger Ka Smaller Ka ==> less % dissed ====> weaker acid

STRENGTH Strong Acid/Base ionize completely equilibrium lies far to the right HCl ------> H+ + Cl- NaOH -----> Na+ + OH- Weak Acid slightly ionize equilibrium lies far to the left HC2H3O2 + H2O <-----> H+ + C2H3O2- IONIZATION CONSTANTS Ka: acid dissociation constant Kb: base dissociation constant

Ka Values MONOPROTIC ACIDS Increasing acid strength Acid Ka Chlorous HClO4 Nitrous HNO2 Hydrofluoric HF Formic HCOOH Acetic CH3COOH Propanoic CH3CH2COOH Hypochlorous HClO Hydrocyanic HCN 1.1*10-2 7.1*10-4 6.8*10-4 1.8*10-4 1.8*10-5 1.3*10-5 2.9*10-8 6.2*10-10

Problem Solving A-B Equilibria Steps 1. Write eqn & Ka/b expression 2. I.C.E. table 3. Define “x” as ; HA 4. Assume “x” very small 5. 5% rule 2 Assumptions 1. [H3O+] from water ignore 2. WA diss little, no  in concen Ka * Kb = Kw

Ka = 6.8*10-4 for 0.75 M hydrofluoric acid solution is. Determine the concentrations of H3O+, A-, & OH-. Also, find the pH, pOH, & % acid dissociation. 1st write eqn & Ka 2nd construct table 3rd determine “change, x” [H3O+] = [F-] Kw = [H3O+] [OH-] 4th assume x negligible; 0.75 - x => 0.75

pH = -Log(0.0223) = 1.65 pOH = 14 - 1.65 = 12.35 OR = -Log(4.4*10-13) = 12.36 % Diss = 0.0223/0.75 * 100 = 3.0 %

HA % Dissociation The initial concen of an acid is 3.2*10-2 then at equilibrium the concen is now 6.4*10-5 What is the % diss? HA% = [HA]diss/[HA]init * 100 HA% = [2.8*10-4]/[1.2*10-2] * 100 = 2.3 %

Classify Acid - Base Strengths WA Halogen acid: HF H not bonded to O: HCN, H2S, H3P Oxo acids: when # O’s < 2 H+ HNO2, HClO2, H3PO3 Carboxylic Acids: - COOH SA Halogen acids: HCl, HBr, HI Oxo acids: when # O’s > 1 H+ HNO3, HClO4, H2SO4 SB Contain O-2 or OH- Group 1A active metals: MOH, M2O Li, Na, K, Rb, Cs Group 2A active metals: M(OH)2, MO Ca, Sr, Ba WB Cmpds w/ e--rich N atom NH3, amines

Ka acetic acid = 1.8*10-5 Ka nitrous acid = 4.4*10-4 nitrous acid more ionized in soln BASE NH3 + H2O <---> NH4+ +OH- Kb ammonia = 1.8*10-5

S.A. yields weak conjugate base W.A. yields strong conj. base MONOPROTIC ACIDS Ka Acid Kb Conj. Base Increasing acid strength Increasing base strength 8.3*10-13 SO4-2 8.3*10-13 ClO2- 1.4*10-11 F- 5.56*10-10 C2H3O2- 2.9*10-7 OCl- 1.8*10-5 NH3 1.2*10-2 HSO4- 1.2*10-2 HClO2 7.2*10-4 HF 1.8*10-5 HC2H3O2 3.5*10-8 HOCl 5.6*10-10 NH4+

acid strength conj. base strength HCl Strong Cl- H2SO4 HSO4- HNO3 NO3- H3O+ H2O HSO4- Weak SO4-2 H2SO3 HSO3- H2PO4 H2PO4- HF F- CH3COOH CH3COO- H2CO3 HCO3- H2S HS- HSO3- SO3-2 H2PO4 HPO4-2 Weak HCN CN- NH4+ NH3 HCO3- CO3-2 HPO4-2 PO4-3 H2O OH- Strong

RXN DIRECTION Direction of SA & SB to form WA & WB H2PO4- + NH3 <------> NH4+ + HPO4-2 H2PO4- SA than NH4+ HS- + H2O <------> H2S + OH- H2S SA than H2O Acid Base rxn goes dir: if HA reacts w/ base lower on list

Diprotic & Triprotic Acids H2CO3: 2 acidic protons Ka values for each H+ Ka1 = 4.3*10-7 Ka2 = 5.6*10-11 typically weak polyprotic acid Ka1 > Ka2 > Ka3 means???? -each step of dissociation is successively weaker -loss of 2nd & 3rd proton occurs less readily Why???? should not be surprising think in terms of charges, +/- being attracted

Various Ways to Describe Acid Strength Property S.A. W.A. Ka value Ka is large Ka is small Position of dissociation equilibrium Far to right Far to left Equilibrium [H+] compared to [HA]o [H+] [HA]o [H+]<<[HA]o Strength of conj.base compared to H2O A- much weaker base than H2O A- much stronger base than H2O

Acid Strength Nonmetal Hydrides The stronger the acid the better it is at donating H+ 2 factors of Acid Strength -- depends how easily the H+ is lost 1) Bond Polarity More polarized bond, quicker H+ lost, greater acid strength 2) Bond Strength Larger “none H” atom is, weaker the bond, greater acid strength Metal Ion Acid Strength high charge density, small metal ions: Fe+3, Al+3, Cu+2, Pb+2, Zn+2, Ni+2

PROPERTIES OF SALTS pH of salt soln: A-B properties of cation & anion 1. SA + SB ----> Neutral 2. SA + WB ----> Acidic 3. WA + SB ---> Basic 1. Cat- & An-ions not react w/ water to form H3O+ or OH- 2. Anion inert; Cation WA, form H3O+ 3. Cation inert; Anion WB, form OH-

4. WA + WB ----> ???? Both ions undergo proton transfer Ka cation > Kb anion: ACIDIC Kb anion > Ka cation: BASIC Ka cation = Kb anion: NEUTRAL

Leveling Effect Lewis Acids - Bases All Bronstad acids form H3O+ in water & bases OH- SA completely form H3O+ SB completely form OH- Lewis Acids - Bases Molecules w/ central atom < 8 val e- Polar molecules w/ dbl bond Metal ions dissolved in water ID Lewis A & B Cl- + BCl3 <----> BCl4- Cl- form coval bond to B; Cl- 4 e- pair BCl3 accepts e- pair, ACID