Acids, Bases, and Salts Preparation for College Chemistry Columbia University Department of Chemistry

Chapter Outline Acids and Bases Definitions The p- function. pH, pK a Titration curves Neutralization reactions and salts Acid Rain

Acids and Bases Definitions Theory Acid Base Arrhenius 1884 Brönsted-Lowry 1923 Lewis 1930’s H-containing, releases H + in water Proton (H + ) donor Electron-pair acceptor OH-containing, releases OH - in water Electron-pair donor Proton (H + ) acceptor

Acid-Base Conjugate Pair acid 1 (aq) + base 2 (aq)base 1 aq) + acid 2 aq) acid 1 (aq)base 1 (aq) + H + (aq) acid 2 base 2 (aq) + H + (aq) HC 2 H 3 O 2 (aq) + H 2 O H 3 O + (aq) + C 2 H 3 O 2 - (aq)

Acidity Constant, K a HC 2 H 3 O 2 (aq) + H 2 O H 3 O + (aq) + C 2 H 3 O 2 - (aq) HCl (aq) + H 2 O H 3 O + (aq) + Cl - (aq) weak acid strong base weak base strong acid K eq = [H 2 O] [H 3 O + ] [C2H3O2 -][C2H3O2 -] [HC 2 H 3 O 2 ] K eq [H 2 O]=KaKa = [H 3 O + ] [C2H3O2 -][C2H3O2 -] [HC 2 H 3 O 2 ] weak base

Basicity Constant, K b NH 4 OH (aq) + H 2 O NH 4 + (aq) + OH - (aq) NaOH (aq) + H 2 O Na + (aq) + OH - (aq) weak acid strong base weak base strong acid strong base K eq = [H 2 O] [NH 4 + ] [OH - ] [NH 4 OH] K eq [H 2 O]=KbKb = [NH 4 + ] [OH - ] [NH 4 OH] weak acid

Acid KaKa Base KbKb 1.8x HCHO 2 2.0x HF HCNO 6.5x HNO 2 HCN HC 2 H 3 O 2 HC 6 H 5 O 2 4.5x x x x NH 3 5.6x N2H2N2H2 1.1x x NH 2 OH PH 3 1.x Mg(OH) 2 1.0x Be(OH) 2 Al(OH) 3 1.9x x K a and K b values Strength

p-function = -log fx [H 3 O + ][OH - ]KwKw ==1x H 2 O + H 2 OH 3 O + (aq) + OH - (aq) log [H 3 O + ] log[OH - ] logK w = = x -1 -log[H 3 O + ] log[OH - ] -logK w = = 14 - p[H 3 O + ]p[OH - ]pK w ==+ 14 pHpHpOH=+ 14

pH Scale [H + ] (mol/L) pH [H + ] (mol/L) pH 1x x x x x x x x x x x x x x Neutral Basicity Acidity

Hydrolysis base (aq) + acid (aq) salt (aq) + H 2 O (l) BaseAcidSalt pH Strong Neutral StrongWeakBasic WeakStrongAcidic Weak Depends on K a and K b

Neutralization Reactions NaOH (aq) + HCl (aq) NaCl (aq) + H 2 O (l) Na + (aq) + OH - (aq) + H + + Cl - (aq)Na + (aq) + Cl - (aq) + H 2 O (l) OH - (aq) + H + H 2 O (l) Net ionic equation: Writing the ionic equation and eliminating SPECTATOR IONS: HC 2 H 3 O 2 (aq) + NaOH (aq) Na C 2 H 3 O 2 (aq) + H 2 O(l) Net ionic equation: HC 2 H 3 O 2 (aq) + OH - (aq)C 2 H 3 O 2 - (aq) + H 2 O (l)

Buffer Solutions Resist changes in pH when small amounts of diluted acids and bases are added. NaC 2 H 3 O 2 (aq)Na + (aq) + C 2 H 3 O 2 - (aq) Two types: Weak acid mixed with its conjugate base Weak base mixed with its conjugate acid HC 2 H 3 O 2 (aq) + H 2 O H 3 O + (aq) + C 2 H 3 O 2 - (aq)

Henderson-Hasselbalch Equation [A - ] KaKa = [H 3 O + ] [HA] Applying p function: -logK a =- log[H 3 O + ]- log A- HA or pK a + log A- HA pH = HA (aq) + H 2 O H 3 O + (aq) + A - (aq)

Replaceable Hydrogens Monoprotic Acids: Diprotic Acids: Polyprotic Acids: HCl, HC 2 H 3 O 2, HNO 3, HC 9 H 19 O 2 H 2 SO 4, H 2 C 2 O 2, H 2 C 2 O 2 H 3 PO 4 The Carboxylic Functional Group C OH O

Titration curves Strong Acid - Strong Base Strong Base - Strong Acid Strong Acid - Weak Base Strong Base - Weak Acid