n Acid/Base Definitions n Types of Acids/bases n Polyprotic Acids n The Ion Product for Water n The pH and Other “p” Scales n Aqueous Solutions of Acids and Bases n Hydrolysis n The Common Ion Effect n Buffer Solutions n Indicators and Titrations n Chapter 15. Acids & Bases

Types of Reactions n a) Precipitation Reactions. n Ionic compounds or salts n b) Acid/base Reactions. n Acids and Bases n c) Redox Reactions. n Oxidizing & Reducing agents

What are Acids &Bases? n Definition? n a) Arrhenius n b) Bronsted-Lowry n c) Lewis

Arrhenius definitions n Acid n AcidAnything that produces hydrogen ions in a water solution. »HCl (aq) H + + Cl - n Base n BaseAnything that produces hydroxide ions in a water solution. »NaOH (aq) Na + + OH - n Arrhenius definitions are limited to aqueous solutions. n Acid base reactions: n HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l)

Brønsted-Lowry definitions n Expands the Arrhenius definitions n Acid n AcidProton donor n Base n BaseProton acceptor n This definition explains how substances like ammonia can act as bases. n Eg. HCl(g) + NH 3 (g) > NH 4 Cl(s) n HCl (acid), NH 3 (base). NH 3 (g) + H 2 O (l) NH OH -

Lewis Definition n Lewis was successful in including acid and bases without proton or hydroxyl ions. n Lewis Acid: A substance that accepts an electron pair. n Lewis base: A substance that donates an electron pair. n E.g. BF 3 (g) + :NH 3 (g) F 3 B:NH 3 (s)

Types of Acids and Bases Binary acids Oxyacid Organic acids Acidic oxides Basic oxides Amine Polyprotic 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

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 perchloric chloric chlorus hyphochlorus

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 They produce oxyacids when dissolved in water

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

Protic Acids Monoprotic Acids: The form protic refers to acidity or 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.

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 or Lewis acid/base definitions.

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

Common acids and bases n Acids n Acids Formula Molarity* n nitricHNO 3 16 n hydrochloric HCl 12 n sulfuricH 2 SO 4 18 n aceticHC 2 H 3 O 2 18 n Bases n ammoniaNH 3 (aq) 15 n sodium hydroxideNaOH solid n *undiluted.

Acids and bases n AcidicBasic n Acidic Basic –Citrus fruitsBaking soda –Aspirin Detergents –Coca Cola Ammonia cleaners –VinegarTums and Rolaids –Vitamin CSoap

Dissociation Equilibrium, n HCl(aq) + H 2 O(l) H 3 + O(aq) + Cl - (aq) n H 2 SO 4 (aq) + H 2 O(l) H 3 + O(aq) + HSO 4 - (aq) n H 2 O(l) + H 2 O(l) H 3 + O(aq) + OH - (aq) n This dissociation is called autoionization of water. n HC 2 H 3 O 2 (aq) + H 2 O(l) H 3 + O(aq) + C 2 H 3 O 2 - (aq) n NH 3 (aq) + H 2 O(l) NH OH - (aq)

Brønsted-Lowry definitions n Conjugate acid-base pairs. n Acids and bases that are related by loss or gain of H + as H 3 O + and H 2 O. Examples. n Examples.AcidBase n H 3 O + H 2 O n HC 2 H 3 O 2 C 2 H 3 O 2 - n NH 4 + NH 3 n H 2 SO 4 HSO 4 - n HSO 4- SO 4 2-

Bronsted acid/conjugate base and base/conjugate acid pairs in acid/base equilibria n HCl(aq) + H 2 O(l) H 3 + O(aq) + Cl - (aq) n HCl(aq): acid n H 2 O(l):base n H 3 + O(aq):conjugate acid n Cl - (aq):conjugate base n H 2 O/ H 3 + O: base/conjugate acid pair n HCl/Cl - :acid/conjugate base pair

Select acid, base, acid/conjugate base pair, base/conjugate acid pair n H 2 SO 4 (aq) + H 2 O(l) H 3 + O(aq) + HSO 4 - (aq) n acid n base n conjugate acid n conjugate base n base/conjugate acid pair acid/conjugate base pair

Equilibrium, Constant, K a & K b n K a : Acid dissociation constant for a equilibrium reaction. n K b : Base dissociation constant for a equilibrium reaction. n Acid: HA + H 2 O H 3 + O + A - n Base: BOH + H 2 O B + + OH - n [H 3 + O][ A - ] [B + ][OH - ] n K a = ; K b = n [HA] [BOH] n

What is K a n HCl(aq) + H 2 O(l) H 3 + O(aq) + Cl - (aq)

n E.g. K a n HCl(aq) + H 2 O(l) H 3 + O(aq) + Cl - (aq) n n [H 3 + O][Cl-] n K a = n [HCl] n [H + ][Cl-] n K a = n [HCl]

What is K a1 and K a2 ? n H 2 SO 4 (aq) + H 2 O(l) H 3 + O(aq) + HSO 4 - (aq) n HSO 4 - (aq) + H 2 O(l) H 3 + O(aq) + SO 4 2- (aq)

What is K b n NH 3 (aq) + H 2 O(l) NH OH - (aq)

n E.g. n H 2 SO 4 (aq) + H 2 O(l) H 3 + O(aq) + HSO 4 - (aq ) n HSO 4 - (aq ) + H 2 O(l) H 3 + O(aq) + SO 4 2- (aq ) n [H 3 + O][HSO 4 - ] n H 2 SO 4 ; K a1 = n [H 2 SO 4 ] n [H 3 + O][ SO 4 2- ] n H 2 SO 4 ; K a2 = n [HSO 4 - ]

E.g. 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 ; K a = [H C 2 H 3 O 2 ] NH 3 (aq) + H 2 O(l) NH OH - (aq) [NH 4 + ][OH - ] NH 3 ; K b = [ NH 3 ]

Which is weaker? n a. HNO 2 ; K a = 4.0 x n b. HOCl 2 ; K a = 1.2 x n c. HOCl ; K a = 3.5 x n d. HCN ; K a = 4.9 x

WEAKER/STRONGER Acids and Bases & K a and K b values n A larger value of K a or K b indicates an equilibrium favoring product side. n Acidity and basicity increase with increasing K a or K b. n pK a = - log K a and pK b = - log K b n Acidity and basicity decrease with increasing pK a or pK b.

Autoionization of water n Autoionization n Autoionization When water molecules react with one another to form ions. n H 2 O (l) + H 2 O (l) H 3 O + (aq) + OH - (aq) – (10 -7 M) (10 -7 M) n K w = [ H 3 O + ] [ OH - ] n = 1.0 x at 25 o C n Note: n Note: [H 2 O] is constant and is n included in K w. ion product of water ion product of water

What is K w ? n H 2 O(l) + H 2 O(l) H 3 + O(aq) + OH - (aq) n This dissociation is called autoionization of water. n Autoionization of water: n K w = [H 3 + O][OH - ] n K w is called ionic product of water n K w = 1 x

Why is water important for acid/base equilibria? n Water is the medium/solvent for acids and bases. n Acids and bases alter the dissociation equilibrium of water based on Le Chaterlier’s principle n H 2 O(l) + H 2 O(l) H 3 + O(aq) + OH - (aq)

Comparing K w and K a & K b n Any compound with a K a value greater than K w of water will be a an acid in water. n Any compound with a K b value greater than K w of water will be a base in water.

pH and other “p” scales n We need to measure and use acids and bases over a very large concentration range. n pH and pOH are systems to keep track of these very large ranges. –pH = -log[H 3 O + ] –pOH = -log[OH - ] –pH + pOH = 14

pH scale n A logarithmic scale used to keep track of the large changes in [H + ] M M 1 M Very Neutral Very Basic Acidic When you add an acid, the pH gets smaller. When you add a base, the pH gets larger.

pH of some common materials 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

What is pH? n K w = [H 3 + O][OH - ] = 1 x n [H 3 + O][OH - ] = x n Extreme cases: n Basic medium n [H 3 + O][OH - ] = x 10 0 n Acidic medium n [H 3 + O][OH - ] = 10 0 x n pH value is -log[H + ] n spans only 0-14 in water.

pH, pK w and pOH n The relation of pH, K w and pOH n K w = [H + ][OH - ] n log K w = log [H + ] + log [OH - ] n -log K w = -log [H + ] -log [OH - ] ; n previous equation multiplied by -1 n pK w = pH + pOH; pK w = 14 n since K w =1 x n 14 = pH + pOH n pH = 14 - pOH n pOH = 14 - pH

Acid and Base Strength n Strong acids n Strong acids Ionize completely in water. HCl, HBr, HI, HClO 3, HNO 3, HClO 4, H 2 SO 4. n Weak acids n Weak acids Partially ionize in water. Most acids are weak. n Strong bases n Strong bases Ionize completely in water. Strong bases are metal hydroxides - NaOH, KOH n Weak bases n Weak bases Partially ionize in water.

pH and pOH calculations of acid and base solutions n 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 n b) weak acids/bases needs K a, K b or percent(%)dissociation

pH of Strong Acid/bases n HNO 3 (aq) + H 2 O(l) H 3 +O(aq) + NO 3 - (aq) n Therefore, the moles of H + ions in the solution is equal to moles of HNO 3 at the beginning. n [HNO 3 ] = [H + ] = 0.2 mole/L n pH = -log [H+] n = -log(0.2) n pH = 0.699

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 ) HSO 4 - (aq ) + H 2 O(l) H 3 + O(aq) + SO 4 2- (aq ) [H 3 + O][HSO 4 - ] H 2 SO 4 ; K a1 = [H 2 SO 4 ] [H 3 + O][ SO 4 2- ] H 2 SO 4 ; K a2 = ; K a2 ignored [HSO 4 - ]

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 ) the moles of H + ions in the solution is equal to moles of H 2 SO 4 at the beginning. [H 2 SO 4 ] = [H + ] = 0.5 mole/L pH = -log [H + ] pH = -log(0.5) pH = 0.30

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