Strong and Weak Acids and Bases Topic 8.3

Acids when a STRONG acid dissolves- all, or nearly all, of the acid molecules react to produce H+ or H3O+ ions (reaction goes to completion) have a very high Kc value HA  H+(aq) + A-(aq) 0% ~100% HA + H2O(l)  H3O+(aq) + A-(aq) 0% ~100% equilibrium is so far to the right for strong acids that we use a yields symbol () instead of an equilibrium symbol (⇌) Initial amount of HA HA H+ A- At Equilibrium

common strong acids (need to know) hydrochloric acid: HCl(g) + H2O(l)  H3O+(aq) + Cl-(aq) nitric acid: HNO3(l) + H2O(l)  H3O+(aq) + NO3-(aq) sulfuric acid: H2SO4(l) + H2O(l)  H3O+(aq) + HSO4-(aq)

when a WEAK acid dissolves, very few acid molecules react to produce H+ ions (equilibrium lies to the left) have a very low Kc value HA ⇌ H+(aq) + A-(aq) 99% ~1% HA + H2O(l) ⇌ H3O+(aq) + A-(aq) 99% ~1% Initial amount of HA HA At Equilibrium HA H+ A-

common weak acids (know these) carboxylic acids (contains one or more carboxyl groups, COOH): acetic acid CH3COOH(l) + H2O(l) ⇌ CH3COO-(aq) + H3O+ carbonic acid: (CO2 in water) CO2(aq) + H2O(l) ⇌ HCO3-(aq) + H+(aq)

Characteristics of strong vs. weak acids equal [conc] of strong and weak acids can be easily distinguished: acid strength does not change when a solution is diluted, only the concentration (molarity) does do not confuse strong and weak, with dilute and concentrated concentrated = high molarity (M) 0.1 M HCl (strong) vs 0.1 M CH3COOH (weak) same concentration, different strength 0.1 mol dm-3 HCl(aq) 0.1 mol dm-3 CH3COOH(aq) [H+(aq)] 0.1 mol dm-3 ~0.0013 mol dm-3 pH 1.00 2.87 Conductivity High Low Reaction Rate with Mg Fast Slow Reaction Rate with CaCO3

strong acids weak acids have more H+ ions, hence lower pH higher conductivity react more vigorously with metals, metal oxides, metal carbonates and bicarbonates have a more (-)∆H of neutralization (more heat) dangerous weak acids opposite of strong acids

Bases when a STRONG base dissolves, nearly all the base molecules react to produce hydroxide (OH-) ions solution have a very high Kc value BOH + (aq)  OH-(aq) + B+(aq) 0% ~100% equilibrium is so far to the right for strong bases that we use a yields symbol () instead of an equilibrium symbol (⇌)

common strong bases all group I hydroxides and barium hydroxide NaOH(s) + (aq)  Na+(aq) + OH-(aq) KOH(s) + (aq)  K+(aq) + OH-(aq) Ba(OH)2(aq) + (aq)  Ba2+(aq) + 2OH-(aq)

when a WEAK base dissolves, very few base molecules react to produce OH- ions have a very low Kc value BOH + (aq) ⇌ OH-(aq) + B+(aq) 99% ~1%

common weak bases ammonia amines (contain NH1,2, or 3) : NH3(g) + (aq) ⇌ NH4+(aq) + OH-(aq) amines (contain NH1,2, or 3) : ethylamine C2N5NH2(g) + H2O(l) ⇌ C2H5NH3+(aq) + OH-(aq)

Strong Bases Weak Bases LiOH NH3 NaOH Amines (ex: C2H5NH2) KOH RbOH CsOH Ba(OH)2

strong vs. weak base characteristics strong bases has more OH- ions, hence higher pH higher conductivity have a more (-)∆H of neutralization (more heat) dangerous weak bases opposite of strong bases

http://phet.colorado.edu/en/simulation/acid-base-solutions

Using experimental data to determine acids and bases Given the following are 0.1 M solutions, determine whether an acid or base, and strength ph of 1: strong acid poor conductor with pH of 6: weak acid fast reaction with magnesium: strong acid [H+] = 10 -10M: weak base [H+] = 10 -4M: weak acid neutralized 0.1M HCl quickly: strong base good conductor with pH of 13: strong base slow reaction with calcium: weak acid has a high -ΔH when reacting with a base: strong acid