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CH. 16 ACID -- BASE 16.1 Definition 16.2 Bronstad-Lowry Conjugate Pairs Strength Leveling Effect 16.3 Dissociation of water K w 16.4 pH scale (pOH) 16.5.

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Presentation on theme: "CH. 16 ACID -- BASE 16.1 Definition 16.2 Bronstad-Lowry Conjugate Pairs Strength Leveling Effect 16.3 Dissociation of water K w 16.4 pH scale (pOH) 16.5."— Presentation transcript:

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

2 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 HNO 3 : one H + H 2 SO 4 : two H + H 3 PO 4 : 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 +

3 TERMS, ETC. ACID:Subst. in H 2 O incr [H + ] BASE:Subst. in H 2 O incr [OH - ] HYDRONIUM ION: H 2 O (l) + H +1 (aq) > H 3 O +1 (aq) Effects H + Ion in H 2 O

4 BRONSTAD-LOWRY ACID:Subst. that donate acidic proton, H + Proton donor BASE:Subst. that gains acidic proton, H + Proton acceptor HCl (g) + H 2 O (l) ----> H 3 O + (aq) + Cl - (aq)

5

6 CONJUGATE ACID-BASE PAIRS Acid, loses H +, form conjugate base Base, gains H +, forms conjugate acid acid 1 acid 2 base 2 base 1 CONJUGATE ACID-BASE PAIRS

7 Fig 16.3 pg. 657

8 RELATIVE STRENGTH H 2 O stronger base than X - X weaker base ---  equilib H 2 O stronger base than Cl - + acid ion of weak acid react w/ H 2 O, produces H 3 O + HX (aq) + H 2 O (l) ----> H 3 O + (aq) + X - (aq) Strong Acid + Weak Base ---  Acidic HCl (g) + H 2 O (l) ----> H 3 O + (aq) + Cl - (aq)

9 X - stronger base than H 2 O CH 3 COO - stronger base than H 2 O CH 3 COOH (aq) + H 2 O (l) ----> H 3 O + (aq) + CH 3 COO - (aq) X stronger base < ---- equilib Weak Acid + Strong Base ---  Basic Proton Transfer: ability of 2 bases attract protons

10 AUTOIONIZATION OF WATER K c [H 2 O] 2 = K w = [H 3 O + ][OH - ] = 1.0* Solution Acid [H 3 O + ] > [OH - ] Neutral [H 3 O + ] = [OH - ] Basic [OH - ] > [H 3 O + ]

11 0 714 pH SCALE STRONG ACIDIC STRONG BASIC MILD ACIDIC MILD BASIC WEAK ACIDIC WEAK BASIC NEUTRAL ( ) K w : constant for water, 1* pK w = -Log [H 2 O] = -Log [1* ] = -Log [ ] -Log [1] = -(-14) - 0 = 14 K w = [H + ][OH - ] 1* = [H + ][OH - ] pK w = pH + pOH pH = -Log [H + ]pOH = -Log [OH - ] [H + ] = 1*10 -pH [OH - ] = 1*10 -pOH Log 1 = 0 Log 10 exp = exp log 10 6 = 6 Log = -4

12 Fig pg 663

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

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

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

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

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

18 TITRATIONS Strong Acid + Strong Base  Neutral Strong Acid + Weak Base ---  Acidic Weak Acid + Strong Base ---  Basic Weak Acid + Weak Base ----  ??????? +/- ions of acid not react w/ H 2 O + acid ion weak acid react w/ H 2 O, produces H 3 O + HBr + NH 4 OH NH 4 is a weak acid reacts w / H 2 O to produce H 3 O + -acid ion weak base produces OH - HCN: CN- is weak base reacts w / H 2 O to produce OH - Both +/- ions react w/ H 2 O

19 DISSOCIATION HA: acid A - : anion K a : acid-dissociation constant Strong Acid -- SA HA (aq) + H 2 O (l ) > H 3 O + (aq) + A - (aq) SA in solution; no HA present, most all H 3 O equilibrium Q c = K c >>>> 1 Weak Acid -- WA HCN (aq) + H 2 O (l ) > H 3 O + (aq) + CN - (aq) WA in solution; no H 3 O + present, most all equilibrium Q c = K c <<<< 1 Stronger Acid ==> higher [H 3 O + ] ===> larger K a Smaller K a ==> less % dissed ====> weaker acid

20 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 HC 2 H 3 O 2 + H 2 O H + + C 2 H 3 O 2 - K a : acid dissociation constant K b : base dissociation constant IONIZATION CONSTANTS

21 Chlorous HClO 4 Nitrous HNO 2 Hydrofluoric HF Formic HCOOH Acetic CH 3 COOH Propanoic CH 3 CH 2 COOH Hypochlorous HClO Hydrocyanic HCN K a Values MONOPROTIC ACIDS Increasing acid strength Acid K a 1.1* * * * * * * *10 -10

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

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

24 pH = -Log(0.0223) = 1.65pOH = = OR = -Log(4.4* ) = % Diss = / 0.75 * 100 = 3.0 %

25 HA % Dissociation HA% = [HA] diss / [HA] init * 100 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% = [2.8*10 -4 ] / [1.2*10 -2 ] * 100 = 2.3 %

26 Classify Acid - Base Strengths SA Halogen acids: HCl, HBr, HI Oxo acids: when # O’s > 1 H + HNO 3, HClO 4, H 2 SO 4 WB Cmpds w / e - -rich N atom NH 3, amines WA Halogen acid: HF H not bonded to O: HCN, H 2 S, H 3 P Oxo acids: when # O’s < 2 H + HNO 2, HClO 2, H 3 PO 3 Carboxylic Acids: - COOH SB Contain O -2 or OH - Group 1A active metals: MOH, M 2 O Li, Na, K, Rb, Cs Group 2A active metals: M(OH) 2, MO Ca, Sr, Ba

27 K a acetic acid = 1.8*10 -5 K a nitrous acid = 4.4*10 -4 nitrous acid more ionized in soln BASE NH 3 + H 2 O NH 4 + +OH - K b ammonia = 1.8*10 -5

28 S.A. S.A. yields weak conjugate base W.A. W.A. yields strong conj. base MONOPROTIC ACIDS Increasing acid strength Increasing base strength K a Acid 1.2*10 -2 HSO *10 -2 HClO 2 7.2*10 -4 HF 1.8*10 -5 HC 2 H 3 O 2 3.5*10 -8 HOCl 5.6* NH * SO * ClO * F * C 2 H 3 O *10 -7 OCl - 1.8*10 -5 NH 3 K b Conj. Base

29 acid strength conj. base strength HCl Strong Cl - H 2 SO 4 HSO 4 - HNO 3 NO 3 - H 3 O + H 2 O HSO 4 - Weak SO 4 -2 H 2 SO 3 HSO 3 - H 2 PO 4 H 2 PO 4 - HF F - CH 3 COOH CH 3 COO - H 2 CO 3 HCO 3 - H 2 S HS - HSO 3 - SO 3 -2 H 2 PO 4 HPO 4 -2 Weak HCN CN - NH 4 + NH 3 HCO 3 - CO 3 -2 HPO 4 -2 PO 4 -3 H 2 O OH - Strong

30 RXN DIRECTION Direction of SA & SB to form WA & WB H 2 PO NH 3 NH HPO 4 -2 HS - + H 2 O H 2 S SA than H 2 O Acid Base rxn goes dir: if HA reacts w / base lower on list H 2 PO 4 - SA than NH 4 + H 2 S + OH -

31 Diprotic & Triprotic Acids H 2 CO 3 : 2 acidic protons K a values for each H + K a1 = 4.3*10 -7 K a2 = 5.6* typically weak polyprotic acid K a1 > K a2 > K a3 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

32 Various Ways to Describe Acid Strength Property S.A. W.A. K a valueK a is large K a 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 H 2 O A - much weaker base than H 2 O A - much stronger base than H 2 O

33 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 Acid Strength Nonmetal Hydrides Metal Ion Acid Strength high charge density, small metal ions: Fe +3, Al +3, Cu +2, Pb +2, Zn +2, Ni +2

34 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 H 3 O + or OH - 2. Anion inert; Cation WA, form H 3 O + 3. Cation inert; Anion WB, form OH -

35 4. WA + WB ----> ???? Both ions undergo proton transfer K a cation > K b anion: ACIDIC K b anion > K a cation: BASIC K a cation = K b anion: NEUTRAL

36 All Bronstad acids form H 3 O + in water & bases OH - SA completely form H 3 O + 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 - + BCl 3 BCl 4 - Cl - form coval bond to B; Cl - 4 e - pair BCl 3 accepts e - pair, ACID Leveling Effect


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