Lecture 142/23/04 ENVIRONMENTAL CLUB MEETING Today at 5:30 BASEMENT OF HAGAN Bonnie Dixon 2:30 at TSC 255 4:30 at TSC 006

Neutralization: Acid + Base = Water + Salt pH of neutralized solution? Weak Acid + Strong Base CH 3 COOH (aq) + NaOH (aq) → H 2 O (l) + NaCl (aq) CH 3 COOH + Na + + OH - → H 2 O + Na + + CH 3 COO - Na + + H 2 O ↔ CH 3 COO - + H 2 O ↔ CH 3 COOH + OH - pH > 7 K b determines pH

Neutralization: Acid + Base = Water + Salt pH of neutralized solution? Strong Acid + Weak Base HCl (aq) + NH 3 (aq) → H 2 O (l) + NH 4 Cl (aq) H + + Cl - + NH 3 → H 2 O + NH Cl - Cl - + H 2 O ↔ ? NH H 2 O ↔ NH 3 + H 3 O + pH < 7 K a determines pH

Neutralization: Acid + Base = Water + Salt pH of neutralized solution? Weak Acid + Weak Base CH 3 COOH + NH 3 → H 2 O + NH 4 CH 3 COO CH 3 COOH + NH 3 → H 2 O + NH CH 3 COO - CH 3 COO - + H 2 O ↔ CH 3 COOH + OH - NH H 2 O ↔ NH 3 + H 3 O + pH depends on K a (NH 4 + ) vs. K b (CH 3 COO - ) K a > K b  acidic K a < K b  basic K a = K b  neutral

Metal hydrolysis Heavy metals as Lewis acids Fe(H 2 O) 6 3+ (aq) ↔ Fe(H 2 O) 5 (OH) 2+ (aq) + H + (aq) K a = 2 x K a generally increases with increasing charge and decreasing radius Fe(H 2 O) 6 2+ (aq) ↔ Fe(H 2 O) 5 (OH) + (aq) + H + (aq) K a = 3.2 x

Amphoteric metals (Al 3+, Cr 3+, Zn 2+, Sn 2+ ) Al(H 2 O) 3 (OH) 3 (s) - insoluble Al(H 2 O) 3 (OH) 3 (s) + OH - → Al(H 2 O) 2 (OH) 4 - (aq) + H 2 O Al(H 2 O) 3 (OH) 3 (s) + H 3 O + → Al(H 2 O) 4 (OH) 2 + (aq) + H 2 O Insoluble metal hydroxides/oxides become more soluble in acid and base solutions

How does changing pH affect solubility? Mg(OH) 2 (s) ↔ Mg 2+ (aq) + 2OH - (aq) Insoluble hydroxide CaCO 3 (s) ↔ Ca 2+ (aq) + CO 3 2- (aq) Anion that is conjugate base of weak acid AgCl (s) ↔ Ag + (aq) + Cl - (aq) Anion that is conjugate base of strong acid

Molecular structure and acid strength Why do some compounds donate H + and some do not? All acidic H bonds are polar bonds Weaker the bond, stronger the acid Non-polar bonds like C-H do not break and H not acidic

Binary Acids Within group: HA bond strength decreases (acid becomes stronger) as A increases with size Acid strength: HF < HCl < HBr < HI Across Row: Stronger acid (more polar - weaker bond) as you move left to right Acid strength: H 2 O < HF Molecular structure and acid strength