16-1 CHEM 102, Fall 2010, LA TECH Instructor: Dr. Upali Siriwardane Office: CTH 311 Phone Office Hours: M,W 8:00-9:00 & 11:00-12:00 am; Tu,Th,F 8: :00 am. Test Dates : September 23, October 21, and November 16; Comprehensive Final Exam: November 18, 2010 Exam: 10:0-10:15 am, CTH 328. September 23, 2010 (Test 1): Chapter 13 October 21, 2010 (Test 2): Chapters 14 & 15 November 16, 2010 (Test 3): Chapters 16, 17 & 18 Comprehensive Final Exam: November 18, 2010 : Chapters 13, 14, 15, 16, 17 and 18 Chemistry 102(01) Fall 2010

16-2 CHEM 102, Fall 2010, LA TECH Chapter 16. Acids and Bases 16.1 The Brønsted-Lowry Concept of Acids and Bases 16.2 Types of acids/bases:Organic Acids and Amines 16.3 The Autoionization of Water 16.4 The pH Scale 16.5 Ionization Constants of Acids and Bases 16.6 Problem Solving Using K a and K b 16.7 Molecular Structure and Acid Strength 16.8 Acid-Base Reactions of Salts 16.9 Practical Acid-Base Chemistry Lewis Acid and Bases

16-3 CHEM 102, Fall 2010, LA TECH Types of Reactions a) Precipitation Reactions. Reactions of ionic compounds or salts Reactions of ionic compounds or salts b) Acid/base Reactions. Reactions of acids and bases Reactions of acids and bases c) Redox Reactions. reactions of oxidizing & reducing agents reactions of oxidizing & reducing agents

16-4 CHEM 102, Fall 2010, LA TECH What are Acids &Bases? Definition? a) Arrhenius b) Bronsted-Lowry c) Lewis

16-5 CHEM 102, Fall 2010, LA TECH Arrhenius, Svante August ( ), Swedish chemist, 1903 Nobel Prize in chemistry AcidAcid Anything that produces hydrogen ions in a water solution. HCl (aq ) H + ( aq) + Cl - ( aq) Base BaseAnything that producs hydroxide ions in a water solution. NaOH (aq) Na + ( aq) + OH - ( aq) Arrhenius definitions are limited proton acids and hydroxide bases to aqueous solutions. Arrhenius Definitions

16-6 CHEM 102, Fall 2010, LA TECH Expands the Arrhenius definitions to include many bases other than hydroxides and gas phase reactions Acid AcidProton donor Base BaseProton acceptor This definition explains how substances like ammonia can act as bases. Eg. HCl(g) + NH 3 (g) > NH 4 Cl(s) HCl (acid), NH 3 (base). NH 3 (g) + H 2 O(l) NH OH - Brønsted-Lowry definitions

16-7 CHEM 102, Fall 2010, LA TECH Lewis Definition G.N. Lewis was successful in including acid and bases without proton or hydroxyl ions. Lewis Acid: A substance that accepts an electron pair. Lewis base: A substance that donates an electron pair. E.g. BF 3 (g) + :NH 3 (g) F 3 B:NH 3 (s) the base donates a pair of electrons to the acid forming a coordinate covalent bond common to coordination compounds. Lewis acids/bases will be discussed later in detail

16-8 CHEM 102, Fall 2010, LA TECH Dissociation Strong Acids: HCl(aq) + H 2 O(l) H 3 + O(aq) + Cl - (aq) HCl(aq) + H 2 O(l) H 3 + O(aq) + Cl - (aq) H 2 SO 4 (aq) + H 2 O(l) H 3 + O(aq) + HSO 4 - (aq) H 2 SO 4 (aq) + H 2 O(l) H 3 + O(aq) + HSO 4 - (aq) Dissociation Equilibrium Weak Acid/base: Dissociation Equilibrium Weak Acid/base: H 2 O(l) + H 2 O(l) H 3 + O(aq) + OH - (aq) This dissociation is called autoionization of water. HC 2 H 3 O 2 (aq) + H 2 O(l) H 3 + O(aq) + C 2 H 3 O 2 - (aq) NH 3 (aq) + H 2 O(l) NH OH - (aq) Equilibrium constants: K a, K b and K w

16-9 CHEM 102, Fall 2010, LA TECH Conjugate acid-base pairs. Acids and bases that are related by loss or gain of H+ as H 3 O + and H 2 O. Examples. Examples.AcidBase H 3 O + H 2 O HC 2 H 3 O 2 C 2 H 3 O 2 - NH 4 + NH 3 H 2 SO 4 HSO 4 - HSO 4 - SO 4 2- Brønsted-Lowry Definitions

16-10 CHEM 102, Fall 2010, LA TECH Bronsted acid/conjugate base and base/conjugate acid pairs in acid/base equilibria HCl(aq) + H 2 O(l) H 3 + O(aq) + Cl - (aq) HCl(aq): acid H 2 O(l):base H 3 + O(aq):conjugate acid Cl - (aq):conjugate base H 2 O/ H 3 + O: base/conjugate acid pair HCl/Cl - :acid/conjugate base pair

16-11 CHEM 102, Fall 2010, LA TECH Select acid, base, acid/conjugate base pair, base/conjugate acid pair H 2 SO 4 (aq) + H 2 O(l) H 3 + O(aq) + HSO 4 - (aq) acid base conjugate acid conjugate base base/conjugate acid pair acid/conjugate base pair

16-12 CHEM 102, Fall 2010, LA TECH Types of Acids and Bases Binary acids: HCl, HBr, HI, H 2 S More than two elements: HCN Oxyacid: HNO 3, H 2 SO 4, H 3 PO 4 Polyprotic acids: H 2 SO 4, H 3 PO 4 Organic acids: R-COOH, R= CH 3 -, CH 3 CH 2 - Acidic oxides: SO 3, NO 2, CO 2, Basic oxides: Na 2 O, CaO Amine: NH 3. R-NH 2, R= CH 3 -, CH 3 CH 2 - : primary R 2 -NH : secondary, R 3 -N: tertiary R 2 -NH : secondary, R 3 -N: tertiary Lewis acids & bases: BF 3 and NH 3

16-13 CHEM 102, Fall 2010, LA TECH Strong Acid vs. Weak Acids Strong acid completely ionized Hydrioidic HI K a ~ pK a = -11 Hydrobromic HBr K a ~ 10 9 pK a = -9 Perchloric HClO 4 K a ~ 10 7 pK a = -7 Hyrdrochloric HCl K a ~ 10 7 pK a = -7 Chloric HClO 3 K a ~ 10 3 pK a = -3 Sulfuric H 2 SO 4 K a ~ 10 2 pK a = -2 Nitric HNO 3 K a ~ 20 pK a = -1.3 Weak acid partially ionized Hydrofluoric acid HF K a = 6.6x10 -4 pK a = 3.18 Formic acid HCOOH K a = 1.77x10 -4 pK a = 3.75 Acetic acid CH 3 COOH K a = 1.76x10 -5 pK a = 4.75 Nitrous acid HNO 2 K a = 4.6x10 -4 pK a = 3.34 Acetyl Salicylic acid C 9 H 8 O 4 K a = 3x10 -4 pK a = 3.52 Hydrocyanic acid HCN K a = 6.17x pK a = 9.21

16-14 CHEM 102, Fall 2010, LA TECH Strong Base vs. Weak Base Strong Base completely ionized Lithium hydroxide LiOH Sodium hydroxide NaOH Potassium hydroxide KOH K b ~ Rubidium hydroxide RbOH Cesium hydroxide CsOH Boarder-line Bases Magnesium hydroxide Mg(OH) 2 Calcium hydroxide Ca(OH) 2 Strotium hydroxide Sr(OH) 2 K b ~ 0.01 to0.1 Barium hydroxide Ba(OH) 2 Weak Base partially ionized Ammonia NH 3 K b =1.79x10 -5 pK b = 4.74 Ethyl amine CH 3 CH 2 NH 2 K b =5.6x10 -4 pK b = 3.25

16-15 CHEM 102, Fall 2010, LA TECH Strong acidsStrong acids Ionize completely in water. HCl, HBr, HI, HClO3, HNO3, HClO4, H2SO4. Weak acidsWeak acids Partially ionize in water. Most acids are weak. Strong basesStrong bases Ionize completely in water. Strong bases are metal hydroxides - NaOH, KOH Weak basesWeak bases Partially ionize in water. Acid and Base Strength

16-16 CHEM 102, Fall 2010, LA TECH Common Acids and Bases Acids Formula Molarity* nitricHNO 3 16 hydrochloric HCl 12 sulfuricH 2 SO 4 18 aceticHC 2 H 3 O 2 18 Bases ammoniaNH 3 (aq) 15 sodium hydroxideNaOH solid *undiluted.

16-17 CHEM 102, Fall 2010, LA TECH Autoionization Autoionization When water molecules react with one another to form ions. Acids and bases alter the dissociation equilibrium of water based on Le Chaterlier’s principle Kw = [ H3O + ] [ OH - ] = 1.0 x at 25 o C Note: Note: [H2O] is constant and is included in Kw. ion product of water ion product of water H2O(l) + H2O(l) H3O + (aq) + OH - (aq) (10 -7 M) (10 -7 M) Autoionization of Water

16-18 CHEM 102, Fall 2010, LA TECH We need to measure and use acids and bases over a very large concentration range. pH and pOH are systems to keep track of these very large ranges. pH = -log[H 3 O + ] pOH = -log[OH - ] pH + pOH = 14 Substance pH 1 M HCl0.0 Gastric juices Lemon juice Classic Coke2.5 Coffee5.0 Pure Water7.0 Blood Milk of Magnesia 10.5 Household ammonia M NaOH 14.0 Substance pH 1 M HCl0.0 Gastric juices Lemon juice Classic Coke2.5 Coffee5.0 Pure Water7.0 Blood Milk of Magnesia 10.5 Household ammonia M NaOH 14.0 pH and other “p” scales

16-19 CHEM 102, Fall 2010, LA TECH A logarithmic scale used to keep track of the large changes in [H + ] M M M Very Neutral Very acidic Basic When you add an acid to, the pH gets smaller. When you add a base to, the pH gets larger. pH scale

16-20 CHEM 102, Fall 2010, LA TECH Substance pH 1 M HCl0.0 Gastric juices Lemon juice Classic Coke2.5 Coffee5.0 Pure Water7.0 Blood Milk of Magnesia 10.5 Household ammonia M NaOH 14.0 Substance pH 1 M HCl0.0 Gastric juices Lemon juice Classic Coke2.5 Coffee5.0 Pure Water7.0 Blood Milk of Magnesia 10.5 Household ammonia M NaOH 14.0 pH of some common materials

16-21 CHEM 102, Fall 2010, LA TECH pH of Aqueous Solutions

16-22 CHEM 102, Fall 2010, LA TECH What is pH? K w = [H 3 + O][OH - ] = 1 x [H 3 + O][OH - ] = x Extreme cases: Extreme cases: Basic medium [H 3 + O][OH - ] = x 10 0 [H 3 + O][OH - ] = x 10 0 Acidic medium [H 3 + O][OH - ] = 10 0 x [H 3 + O][OH - ] = 10 0 x pH value is -log[H + ] spans only 0-14 in water.

16-23 CHEM 102, Fall 2010, LA TECH pH, pK w and pOH The relation of pH, K w and pOH K w = [H + ][OH - ] K w = [H + ][OH - ] log K w = log [H + ] + log [OH - ] log K w = log [H + ] + log [OH - ] -log K w = -log [H + ] -log [OH - ] ; -log K w = -log [H + ] -log [OH - ] ; previous equation multiplied by -1 pK w = pH + pOH; pK w = 14 pK w = pH + pOH; pK w = 14 since K w =1 x since K w =1 x = pH + pOH pH = 14 - pOH pOH = 14 - pH 14 = pH + pOH pH = 14 - pOH pOH = 14 - pH

16-24 CHEM 102, Fall 2010, LA TECH pH and pOH calculations of acid and base solutions a) Strong acids/bases dissociation is complete for strong acid such as HNO 3 or base NaOH [H + ] is calculated from molarity (M) of the solution b) weak acids/bases needs K a, K b or percent(%)dissociation

16-25 CHEM 102, Fall 2010, LA TECH pH of Strong Acid/bases HNO 3 (aq) + H 2 O(l) H 3 +O(aq) + NO 3 - (aq) HNO 3 (aq) + H 2 O(l) H 3 +O(aq) + NO 3 - (aq) Therefore, the moles of H + ions in the solution is equal to moles of HNO 3 at the beginning. [HNO 3 ] = [H + ] = 0.2 mole/L [HNO 3 ] = [H + ] = 0.2 mole/L pH = -log [H+] pH = -log [H+] = -log(0.2) = -log(0.2) pH = pH = Substance pH 1 M HCl0.0 Gastric juices Lemon juice Classic Coke2.5 Coffee5.0 Pure Water7.0 Blood Milk of Magnesia 10.5 Household ammonia M NaOH 14.0 Substance pH 1 M HCl0.0 Gastric juices Lemon juice Classic Coke2.5 Coffee5.0 Pure Water7.0 Blood Milk of Magnesia 10.5 Household ammonia M NaOH 14.0

16-26 CHEM 102, Fall 2010, LA TECH pH of 0.5 M H 2 SO 4 Solution H 2 SO 4 (aq) + H 2 O(l) H 3 + O(aq) + HSO 4 - (aq ) H 2 SO 4 (aq) + H 2 O(l) H 3 + O(aq) + HSO 4 - (aq ) HSO 4 - (aq ) + H 2 O(l) H 3 + O(aq) + SO 4 2- (aq ) HSO 4 - (aq ) + H 2 O(l) H 3 + O(aq) + SO 4 2- (aq ) [H 3 + O][HSO 4 - ] [H 3 + O][HSO 4 - ] H 2 SO 4 ; K a1 = H 2 SO 4 ; K a1 = [H 2 SO 4 ] [H 2 SO 4 ] [H 3 + O][ SO 4 2- ] [H 3 + O][ SO 4 2- ] H 2 SO 4 ; K a2 = ; K a2 ignored H 2 SO 4 ; K a2 = ; K a2 ignored [HSO 4 - ] [HSO 4 - ]

16-27 CHEM 102, Fall 2010, LA TECH H2SO4(aq) + H2O(l) H3 + O(aq) + HSO4 - (aq ) the moles of H + ions in the solution is equal to moles of H2SO4 at the beginning. [H2SO4] = [H + ] = 0.5 mole/L pH = -log [H + ] pH = -log(0.5) pH = 0.30 pH of 0.5 M H 2 SO 4 Solution

16-28 CHEM 102, Fall 2010, LA TECH 1.5 x M NaOH. NaOH is also a strong base dissociates completely in water. NaOH is also a strong base dissociates completely in water. [NaOH] = [HO - ] = 1.5 x mole/L [NaOH] = [HO - ] = 1.5 x mole/L pOH = -log[HO - ]= -log(1.5 x ) pOH = -log[HO - ]= -log(1.5 x ) pOH = 1.82 pOH = 1.82 As defined and derived previously: As defined and derived previously: pK w = pH + pOH; pK w = 14 pH = pK w + pOH pH = 14 - pOH pH = ; pH = 12.18

16-29 CHEM 102, Fall 2010, LA TECH Mixtures of Strong and Weak Acids the presence of the strong acid retards the dissociation of the weak acid

16-30 CHEM 102, Fall 2010, LA TECH Measuring pH Arnold Beckman inventor of the pH meter father of electronic instrumentation

16-31 CHEM 102, Fall 2010, LA TECH Equilibrium, Constant, K a & K b K a : Acid dissociation constant for a equilibrium reaction. K b : Base dissociation constant for a equilibrium reaction. Acid: HA + H 2 O H 3 + O + A - Base: BOH + H 2 O B + + OH - [H 3 + O][ A - ] [B + ][OH - ] K a = ; K b = [HA] [BOH]

16-32 CHEM 102, Fall 2010, LA TECH HCl(aq) + H 2 O(l) H 3 + O(aq) + Cl - (aq) HCl(aq) + H 2 O(l) H 3 + O(aq) + Cl - (aq) [H 3 + O][Cl-] [H 3 + O][Cl-] K a = [HCl] [HCl] [H + ][Cl-] [H + ][Cl-] K a = [HCl] [HCl] Acid Dissociation Constant

16-33 CHEM 102, Fall 2010, LA TECH Base Dissociation Constant NH 3 + H 2 O NH OH - [NH 4 + ][OH - ] K = [NH 3 ]

16-34 CHEM 102, Fall 2010, LA TECH Hydrated Metal Ions as Acids

16-35 CHEM 102, Fall 2010, LA TECH Ionization Constants for Acids

16-36 CHEM 102, Fall 2010, LA TECH Comparing K w and K a & K b Any compound with a K a value greater than K w of water will be a an acid in water. Any compound with a K b value greater than K w of water will be a base in water.

16-37 CHEM 102, Fall 2010, LA TECH WEAKER/STRONGER Acids and Bases & K a and K b values A larger value of K a or K b indicates an equilibrium favoring product side. Acidity and basicity increase with increasing K a or K b. Acidity and basicity increase with increasing K a or K b. pK a = - log K a and pK b = - log K b Acidity and basicity decrease with increasing pK a or pK b.

16-38 CHEM 102, Fall 2010, LA TECH Which is weaker? a. HNO 2 ; K a = 4.0 x b. HOCl 2 ; K a = 1.2 x c. HOCl ; K a = 3.5 x d. HCN ; K a = 4.9 x

16-39 CHEM 102, Fall 2010, LA TECH What is K a1 and K a2 ? H 2 SO 4 (aq) + H 2 O(l) H 3 + O(aq) + HSO 4 - (aq) HSO 4 - (aq) + H 2 O(l) H 3 + O(aq) + SO 4 2- (aq)

16-40 CHEM 102, Fall 2010, LA TECH H 2 SO 4 (aq) + H 2 O(l) H 3 + O(aq) + HSO 4 - (aq ) HSO 4 - (aq ) + H 2 O(l) H 3 + O(aq) + SO 4 2- (aq ) [H 3 + O][HSO 4 - ] [H 3 + O][HSO 4 - ] H 2 SO 4 ; K a1 = [H 2 SO 4 ] [H 2 SO 4 ] [H 3 + O][SO 4 2- ] H 2 SO 4 ; K a2 = [HSO 4 - ] [HSO 4 - ] K a Examples

16-41 CHEM 102, Fall 2010, LA TECH HC 2 H 3 O 2 (aq) + H 2 O(l) H 3 + O(aq) + C 2 H 3 O 2 - (aq) [H + ][C 2 H 3 O 2 - ] [H + ][C 2 H 3 O 2 - ] H C 2 H 3 O 2 ; K a = H C 2 H 3 O 2 ; K a = [H C 2 H 3 O 2 ] [H C 2 H 3 O 2 ] NH 3 (aq) + H 2 O(l) NH OH - (aq) [NH 4 + ][OH - ] [NH 4 + ][OH - ] NH 3 ; K b = NH 3 ; K b = [ NH 3 ] [ NH 3 ] K a Examples

16-42 CHEM 102, Fall 2010, LA TECH How do you calculate pH of weak acids/bases From % dissociation From K a or K b What is % dissociation Amount dissociated Amount dissociated % Dissoc. = x 100 Initial amount Initial amount

16-43 CHEM 102, Fall 2010, LA TECH How do you calculate % dissociation from K a or K b 1.00 M solution of HCN; K a = 4.9 x What is the % dissociation for the acid?

16-44 CHEM 102, Fall 2010, LA TECH 1.00 M solution of HCN; K a = 4.9 x First write the dissociation equilibrium equation: First write the dissociation equilibrium equation: HCN(aq) + H 2 O(l) H 3 + O(aq) + CN - (aq) [HCN] [H + ] [CN - ] [HCN] [H + ] [CN - ] Ini. Con M 0.0 M 0.00 M Cha. Con -x x x Eq. Con x x x [H 3 + O ][CN - ] x 2 [H 3 + O ][CN - ] x 2 K a = = K a = = [HCN] x [HCN] x 1.00 M solution of HCN; K a = 4.9 x

16-45 CHEM 102, Fall 2010, LA TECH x ~ 1.00 since x is small x 2 x 2 K a = ; K a =4.9 x = x 2 K a = ; K a =4.9 x = x x = 4.9 x = 2.21 x x = 4.9 x = 2.21 x Amount disso x x 100 = x 100 Ini. amount 1.00 Ini. amount 1.00 % Diss.=2.21 x x 100 = % % Diss.=2.21 x x 100 = % 1.00 M solution of HCN; K a = 4.9 x

16-46 CHEM 102, Fall 2010, LA TECH % Dissociation gives x (amount dissociated) need for pH calculation Amount dissociated Amount dissociated % Dissoc. = x 100 Initial amount/con. Initial amount/con. x % Dissoc. = x 100 % Dissoc. = x 100 concentration concentration

16-47 CHEM 102, Fall 2010, LA TECH 1 M HF, 2.7% dissociated Notice the conversion of % dissociation to a fraction (x): 2.7/100=0.027) x=0.027 Calculate the pH of a weak acid from % dissociation

16-48 CHEM 102, Fall 2010, LA TECH HF(aq) + H 2 O(l) H 3 + O(aq) + F - (aq) [H + ][F - ] [H + ][F - ] K a = [HF] [HF] [HF] [H + ] [F - ] [HF] [H + ] [F - ] Ini. Con M 0.0 M0.00 M Chg. Con -x x x Eq.Con pH = -log [H + ] pH = -log [H + ] pH = -log(0.027) pH = -log(0.027) pH = 1.57 pH = 1.57 Calculate the pH of a weak acid from % dissociation

16-49 CHEM 102, Fall 2010, LA TECH Weak acid Equilibria Example Determine the pH of a 0.10 M benzoic acid solution at 25 o C if K a = 6.28 x HBz (aq) + H 2 O (l) H 3 O + (aq) + Bz -(aq) The first step is to write the equilibrium expression K a = K a = [H 3 O + ][Bz - ] [HBz]

16-50 CHEM 102, Fall 2010, LA TECH Weak acid Equilibria HBz H 3 O + Bz - HBz H 3 O + Bz - Initial conc., M Change,  M -x x x Eq. Conc., M x x x [H 3 O + ] = [Bz - ] = x We’ll assume that [Bz - ] is negligible compared to [HBz]. The contribution of H 3 O + from water is also negligible.

16-51 CHEM 102, Fall 2010, LA TECH Weak Acid Equilibria Solve the equilibrium equation in terms of x K a = 6.28 x = x = (6.28 x )(0.10) H 3 O + = M H 3 O + = M pH= 2.60 x

16-52 CHEM 102, Fall 2010, LA TECH pH from K a or K b 1.00 M solution of HCN; K a = 4.9 x First write the dissociation equilibrium equation: First write the dissociation equilibrium equation: HCN(aq) + H 2 O(l) H 3 + O(aq) + CN - (aq) [HCN] [H + ] [CN - ] [HCN] [H + ] [CN - ] Ini. Con M 0.0 M 0.00 M Chg. Con -x x x Eq. Con x x x

16-53 CHEM 102, Fall 2010, LA TECH [H 3 + O ][CN - ] x 2 [H 3 + O ][CN - ] x 2 K a = = K a = = [HCN] x [HCN] x x ~ 1.00 since x is small x ~ 1.00 since x is small x 2 x 2 K a = ; K a =4.9 x = x 2 K a = ; K a =4.9 x = x x = 4.9 x = 2.21 x x = 4.9 x = 2.21 x pH = -log [H + ] pH = -log [H + ] pH = -log(2.21 x ) pH = -log(2.21 x ) pH = 4.65 pH = 4.65 Weak Acid Equilibria

16-54 CHEM 102, Fall 2010, LA TECH The Conjugate Partners of Strong Acids and Bases The conjugate acid/base of a strong base/acid has no net effect on the pH of a solution The conjugate base of a weak acid hydrolyze in water and basic or pH of a solution > 7.00 E.g. Na + C 2 H 3 O 2 - sodium acetate The conjugate acid of a weak base hydrolyze in water and acidic or pH of a solution < 7.00 E.g NH 4 Cl

16-55 CHEM 102, Fall 2010, LA TECH Reaction of a basic anion or acidic cation with water is an ordinary Brønsted-Lowry acid-base reaction. CH3COO - (aq) + H2O (l) CH3COOH (aq) + OH - (aq) NH4 + (aq) + H2O (l) NH3 (aq) + H3O + (aq) This type of reaction is given a special name.Hydrolysis The reaction of an anion with water to produce the conjugate acid and OH -. The reaction of a cation with water to produce the conjugate base and H3O +.Hydrolysis

16-56 CHEM 102, Fall 2010, LA TECH Acid-Base Properties of Typical Ions

16-57 CHEM 102, Fall 2010, LA TECH What salt solutions would be acidic, basic and neutral? 1)strong acid + strong base = neutral 2)weak acid + strong base = basic 3)strong acid + weak base = acidic 4) weak acid + weak base = neutral, basic or an acidic solution depending on the relative strengths of the acid and the base. basic or an acidic solution depending on the relative strengths of the acid and the base.

16-58 CHEM 102, Fall 2010, LA TECH What pH? Neutral, basic or acidic? a)NaCla)NaCl neutral neutral b) NaC 2 H 3 O 2b) NaC 2 H 3 O 2 basic basic c) NaHSO 4c) NaHSO 4 acidic acidic d) NH 4 Cld) NH 4 Cl acidic acidic

16-59 CHEM 102, Fall 2010, LA TECH How do you calculate pH of a salt solution? Find out the pH, acidic or basic? If acidic it should be a salt of weak base If basic it should be a salt of weak acid if acidic calculate K a from K a = K w /K b if basic calculate K b from K b = K w /K a Do a calculation similar to pH of a weak acid or base

16-60 CHEM 102, Fall 2010, LA TECH What is the pH of 0.5 M NH 4 Cl salt solution? (NH 3 ; K b = 1.8 x ) Find out the pH, acidic if acidic calculate K a from K a = K w /K b K a = K w /K b = 1 x /1.8 x ) K a = X Do a calculation similar to pH of a weak acid

16-61 CHEM 102, Fall 2010, LA TECH Continued NH H 2 O H 3 + O + NH 3 NH H 2 O H 3 + O + NH 3 [NH 4 + ] [H 3 + O ] [NH 3 ] [NH 4 + ] [H 3 + O ] [NH 3 ] Ini. Con. 0.5 M 0.0 M0.00 M Change -x x x Eq. Con x x x [H 3 + O ] [NH 3 ] [H 3 + O ] [NH 3 ] K a (NH 4 + ) = = [NH 4 + ] [NH 4 + ] x 2 x ; appro.:0.5 - x. 0.5 (0.5 - x) (0.5 - x)

16-62 CHEM 102, Fall 2010, LA TECH x 2 x 2 K a (NH 4 + ) = = 5.56 x x 2 = 5.56 x x 0.5 = 2.78 x x 2 = 5.56 x x 0.5 = 2.78 x x= 2.78 x = 1.66 x [H + ] = x = 1.66 x M pH = -log [H + ] = - log 1.66 x pH = 4.77 pH of 0.5 M NH 4 Cl solution is 4.77 (acidic ) Continued

16-63 CHEM 102, Fall 2010, LA TECH Types of Acids and Bases Binary acids Oxyacid Organic acids Acidic oxides Basic oxides Amine Polyprotic acids

16-64 CHEM 102, Fall 2010, LA TECH Influence of Molecular Structure on Acid Strength Binary Hydrides hydrogen & one other element Bond Strengths weaker the bond, the stronger the acid Stability of Anion higher the electronegativity, stronger the acid

16-65 CHEM 102, Fall 2010, LA TECH Binary Acids Binary Acids Compounds containing acidic protons bonded to a more electronegative atom. e.g. HF, HCl, HBr, HI, H 2 S The acidity of the haloacid (HX; X = Cl, Br, I, F) Series increase in the following order: HF < HCl < HBr < HI HF < HCl < HBr < HI

16-66 CHEM 102, Fall 2010, LA TECH Oxyacids Oxyacids Compounds containing acidic - OH groups in the molecule. Acidity of H 2 SO 4 is greater than H 2 SO 3 because of the extra O (oxygens) The order of acidity of oxyacids from the a halogen (Cl, Br, or I) shows a similar trend. HClO 4 > HClO 3 > HClO 2 > HClO HClO 4 > HClO 3 > HClO 2 > HClO perchloric chloric chlorus hyphochlorus perchloric chloric chlorus hyphochlorus

16-67 CHEM 102, Fall 2010, LA TECH Influence of Molecular Structure on Acid Strength Oxyacids hydrogen, oxygen, & one other elementH-O-E higher the electronegativity on E, stronger the acid as this weakens the bond between the O and H

16-68 CHEM 102, Fall 2010, LA TECH <<< < Oxo Acid

16-69 CHEM 102, Fall 2010, LA TECH Acidic Oxides Acidic Oxides These are usually oxides of non-metallic elements such as P, S and N. E.g. NO 2, SO 2, SO 3, CO 2 E.g. NO 2, SO 2, SO 3, CO 2 They produce oxyacids when dissolved in water SO3 + H2O ---> H2SO4 CO2 + H2O ---> H2CO3 NO2 + H2O ---> HNO3

16-70 CHEM 102, Fall 2010, LA TECH Basic Oxides Basic Oxides Oxides oxides of metallic elements such as Na, K, Ca. They produce hydroxyl bases when dissolved in water. e.g. CaO + H 2 O ---> Ca(OH) 2 Na 2 O + H 2 O ---> 2 NaOH Na 2 O + H 2 O ---> 2 NaOH

16-71 CHEM 102, Fall 2010, LA TECH Protic Acids Monoprotic Acids: The form protic refers to acidity due to protons. Monoprotic acids have only one acidic proton. e.g. HCl. Polyprotic Acids: They have more than one acidic proton. e.g. H 2 SO 4 - diprotic acid H 3 PO 4 - triprotic acid.

16-72 CHEM 102, Fall 2010, LA TECH Polyprotic Acids acids where more than one hydrogen per molecule is released

16-73 CHEM 102, Fall 2010, LA TECH Polyprotic Acids

16-74 CHEM 102, Fall 2010, LA TECH Organic or Carboxylic Acids

16-75 CHEM 102, Fall 2010, LA TECH FCH 2 CO 2 H (strongest acid) > ClCH 2 CO 2 H > BrCH 2 CO 2 H (weakest acid). FCH 2 CO 2 H (strongest acid) > ClCH 2 CO 2 H > BrCH 2 CO 2 H (weakest acid). Acid K a pK a HCOOH (formic acid) 1.78 X CH 3 COOH (acetic acid) 1.74 X CH 3 CH 2 COOH (propanoic acid)1.38 x Organic or Carboxylic Acids

16-76 CHEM 102, Fall 2010, LA TECH Amines Amines Class of organic bases derived from ammonia NH 3 by replacing hydrogen by organic groups. They are defined as bases similar to NH 3 by Bronsted- Lowery or Lewis acid/base definitions.

16-77 CHEM 102, Fall 2010, LA TECH Amines

16-78 CHEM 102, Fall 2010, LA TECH Acid-Base Chemistry of Some Antacids

16-79 CHEM 102, Fall 2010, LA TECH Acid-Base in the Kitchen vinegar - acetic acid lemon juice (citrus juice) - citric acid baking soda - NaHCO 3 milk - lactic acid baking powder - H 2 PO 4 - & HCO 3 -

16-80 CHEM 102, Fall 2010, LA TECH Household Cleaners

16-81 CHEM 102, Fall 2010, LA TECH Dishwashing Detergent

16-82 CHEM 102, Fall 2010, LA TECH Lewis Definition G.N. Lewis was successful in including acid and bases without proton or hydroxyl ions. Lewis Acid: A substance that accepts an electron pair. Lewis base: A substance that donates an electron pair. E.g. BF 3 (g) + :NH 3 (g) F 3 B:NH 3 (s) the base donates a pair of electrons to the acid forming a coordinate covalent bond common to coordination compounds. Lewis acids/bases will be discussed later in detail

16-83 CHEM 102, Fall 2010, LA TECH Lewis Acids and Bases Reactions H + + NH 3     acid base acid base Cu NH 3  [Cu(NH 3 ) 4 +2 ] acid base acid base

16-84 CHEM 102, Fall 2010, LA TECH What acid base concepts (Arrhenius/Bronsted/Lewis) would best describe the following reactions: a) HCl(aq) + NaOH(aq) ---> NaCl(aq) + H 2 O(l) b)HCl(g) + NH 3 (g) --->NH 4 Cl(s) c)BF 3 (g) + NH 3 (g)--->F 3 B:NH 3 (s) d)Zn(OH) 2 (s) + 2OH - (aq) ---> [Zn(OH) 4 ] 2- (aq)