Chem 108 1st Edition Lecture 18Current LectureChapter 16 Acid–Base and Solubility EquilibriumArrhenius Acids and Bases- Arrhenius acid: an Arrhenius acid will increase proton concentration in water - Arrhenius base: an Arrhenius base will increase hydroxide concentration in waterHydronium Ion:- H+ associate with water molecules to produce complex ions H+ + nH2O H(H2O)n+o H+ is proton and H+ is solvated by water solvated o H+ is called hydronium ion hydration by one water moleculeBrønsted-Lowry Model:- Brønsted-Lowry acid = H+ ion donor. - Brønsted-Lowry base = H+ ion acceptor- NH3 (aq) + H2O(l) NH4+ (aq) + OH (aq) H2O is acid, NH3 is base- Water can act as both a Brønsted-Lowry acid and baseo H2O + H2O H3O+ + OH-o Water can both donate and accept H+ ionsAcid Ionization Constant, Ka- Acid strength is measured by the size of the equilibrium constant when it reacts with H2O o HAcid + H2O Acid− + H3O- The equilibrium constant for this reaction is called the acid ionization constant, Kao Ka= ([Acid−][ H3O])/( HAcid[H2O])o larger Ka = stronger acido strong acids completely ionized in water, Strong acids: Ka >>1o weak acids only partially ionized in water, Weak Acids: Ka < 1Conjugate acid-base pairs:- Differ from each other only by the presence or absence of a proton-o The strongest acid have the weakest conjugate base o The weakest acid has the strongest conjugate base.o But in between there are weak acids that are paired with weak bases Lewis Acids and Bases:- Lewis acid: electron pair acceptor - Lewis base: electron pair donor - H+ and OH do not necessarily have to be involved - Electron pairs of one reactant (the Lewis base) attracted to positively charged regions of another reactant (the Lewis acid) o positively charged transition metal ions act as Lewis acidsWater: An Amphiprotic Substance- Amphiprotic: Capable of acting as an acid or a base. - Water as a base: HNO3 (aq) (H+ donor) + H2O(l) (H+ acceptor) → NO3 − (aq) + H3O+ (aq) - Water as an acid: NH3 (aq) (H+ acceptor) + H2O(l) (H+ donor) ⇌ NH4 + (aq) + OH− (aq) Relative Strengths of Acids and Bases:- Leveling Effect: H3O+ is the strongest H+ donor that can exist in water, and Acids can only get strong to a point because of it. Strong acids all have the same strength in water; are completely converted into H3O+ ions.- Any base stronger than OH- hydrolyzes in water to produce OH- ions- The most common strongest bases are the hydroxides of group 1 and 2
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