Acids and Bases intro
Acid/Base Definitions Arrhenius Model Acids produce hydrogen ions in aqueous solutions Bases produce hydroxide ions in aqueous solutions Bronsted-Lowry Model Acids are proton donors Bases are proton acceptors
Acid Dissociation HA H + + A - Acid Proton Conjugate base Alternately, H + may be written in its hydrated form, H 3 O + (hydronium ion)
for example… HCl H + + Cl - Acid Proton Conjugate base
Dissociation of Strong Acids Strong acids are assumed to dissociate completely in solution. Large K a or small K a ? Reactant favored or product favored?
Dissociation Constants: Strong Acids AcidFormula Conjugate Base KaKa Perchloric HClO 4 ClO 4 - Very large Hydriodic HI I - Very large Hydrobromic HBr Br - Very large Hydrochloric HCl Cl - Very large Nitric HNO 3 NO 3 - Very large Sulfuric H 2 SO 4 HSO 4 - Very large Hydronium ion H 3 O + H 2 O 1.0
Dissociation of Weak Acids Weak acids are assumed to dissociate only slightly (less than 5%) in solution. Large K a or small K a ? Reactant favored or product favored?
Dissociation Constants: Weak Acids AcidFormula Conjugate Base KaKa Iodic HIO 3 IO x Oxalic H 2 C 2 O 4 HC 2 O x Sulfurous H 2 SO 3 HSO x Phosphoric H 3 PO 4 H 2 PO x Citric H 3 C 6 H 5 O 7 H 2 C 6 H 5 O x Nitrous HNO 2 NO x Hydrofluoric HF F x Formic HCOOH HCOO x Benzoic C 6 H 5 COOH C 6 H 5 COO x Acetic CH 3 COOH CH 3 COO x Carbonic H 2 CO 3 HCO x Hypochlorous HClO ClO x Hydrocyanic HCN CN x
Self-Ionization of Water H 2 O + H 2 O H 3 O + + OH - At 25 , [H 3 O + ] = [OH - ] = 1 x K w is a constant at 25 C: K w = [H 3 O + ][OH - ] K w = (1 x )(1 x ) = 1 x
Calculating pH, pOH pH = -log 10 (H 3 O + ) pOH = -log 10 (OH - ) Relationship between pH and pOH pH + pOH = 14 Finding [H 3 O + ], [OH - ] from pH, pOH [H 3 O + ] = 10 -pH [OH - ] = 10 -pOH
pH and pOH Calculations
pH Scale