Tài liệu Chapter 6: Chemical Equilibrium ppt

Chapter 6: Chemical Equilibrium I. The Chemical Composition of Aqueous Solutions Electrolytes: solutes which carry electrical charge - these compounds are at least partially ionized 1. Strong Electrolytes = solutes almost completely ionized 2. Weak Electrolytes = solutes only partially ionized Acids and Bases - electrolytes (can be weak or strong) 1. Bronsted-Lowery Theory: ¾ acids are proton donors ¾ bases are proton acceptors 2. Strong Acids and bases almost completely ionized 3. Weak acids and bases (poorly ionized). See Table 6-2 (memorize strong acids and bases) a. Conjugate acids and bases: when an acid donates a proton in an acid-base reaction, it forms a conjugate base. Likewise, when a base accepts a proton in an acid-base reaction it forms a conjugate acid. H 2 O (base) + HCOOH (acid) <===> H 3 O + (conj. acid) + HCOO - (conj. base) b. Amphiprotic solvents can be either acids or bases: H 2 O (acid) + CH 3 NH 2 (base) <===> OH - (conj. base) + CH 3 NH 3 + (conj. acid) c. Autoprotolysis: when amphiprotic solvents undergo self-ionization 2 H 2 O <=====> H 3 O + + OH - K w This expression is called the ion-product of water and is denoted K w = [H 3 O + ][OH - ] K w = 1.01 x 10 -14 at 25°C pK w = -log K w = -log 1.01 x 10 -14 = 14 Acid and Base Strengths Acid and base strengths may be determined by using ¾ a differentiating solvent . That is, selecting a solvent which will accept (or donate) a proton to one acid (or base) but not another (example: use of glacial acetic acid as solvent to compare HClO 4 and HCl acid strength). ¾ a leveling solvent is one in which all acids or bases are dissociated to the same degree and have equal acid (or base) strengths. ¾a differentiating solvent CH 3 COOH + HClO 4 CH 3 COOH 2 + +ClO 4 - CH 3 COOH + HCl CH 3 COOH 2 + +Cl - ¾ a leveling solvent (H 2 O) HClO 4 + H 2 O H 3 O + +ClO 4 - HCl + H 2 O H 3 O + +Cl - <====> <====> Table: Acids and Bases Any Questions? II. Chemical Equilibrium: The ratio of the molar concentrations of reactants and products is a constant at certain temperature. H 2 O + HCOOH <===> H 3 O + + HCOO - The square bracketed terms mean: ¾ Molar concentration if the species is a dissolved solute ¾ Partial pressure in atm if species is a gas ¾ Unity if species is a pure liquid, pure solid, or pure solvent (solvent in an extremely dilute solution). ]HCOOH][OH[ ]HCOO][OH[ K 2 - 3 a + = [...]... for [OH-] solved for − [OH ] = K b C b Kw [H 3O ] = − [OH ] + Any Questions? Summary Acids and Bases: concepts and strength of Acids and Bases Equilibrium- constant expression Types of Equilibrium constants (Table 7-2) P-functions Common-ion effect Calculation of equilibrium constants and concentrations (e.g.) Ion-product constant for water Solubility-product constants Acid and Base Dissociation Constants... that cHA = [A-] + [HA] (analytical concentration) cHA = [H3O+] + [HA] or [HA] = cHA - [H3O+] Equilibrium expression for the acid dissociation: + 2 [H 3O ] Ka = + (C HA - [H 3O ]) [H3O+]2 + Ka[H3O+] - KacHA = 0 The positive solution to the quadratic equation is: 2 − K a + K a + 4K a C HA [H 3O ] = 2 + Simplified Equilibrium Expression • Assume cHA >> [H3O+]) : [H3O+]2 = cHAKa or [H 3O + ] = K a C HA •...III Types of Equilibrium Constants (See Table 6-1) A The ion-product for water Water is poorly dissociated, but does undergo autoprotolysis: 2 H2O H3O+ + OH- and, recalling that molar concentrations = 1 for dilute... we can write the solubility product: [Fe+3] [OH-]3 = Ksp = 4 x 10-38 Any Questions? The common ion effect • Based upon Le Chatelier's Principle, if we add an ion common to the solid to the medium, the equilibrium will shift to make the solid less soluble THIS IS ALSO CALLED A MASS-ACTION EFFECT Example 6-1: The common ion effect 1 The solubility, x, of Fe(OH)3 in pure water ([OH-] = 10–7 M) is: Fe(OH)3 . Chapter 6: Chemical Equilibrium I. The Chemical Composition of Aqueous Solutions Electrolytes:. +Cl - <====> <====> Table: Acids and Bases Any Questions? II. Chemical Equilibrium: The ratio of the molar concentrations of reactants and products