University:
Kentucky State University
Course:
CHE 102 | General Chemistry II
Academic year:

2024
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398

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13
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MoGhoadoAnotozj14

Chapter 9 Aqueous Solutions and Chemical Equilibria Solutions of Electrolytes Electrolytes: Form ions when dissolved in water or other solvents and produce solutions that conduct electricity. Strong Electrolytes: Ionize essentially completely (Strong conductor of electricity). Weak Electrolytes: Ionize only partially (Poorer conductor than strong electrolyte). Nonelectrolytes: Are substances that dissolve in water but do not produce any ions and do not conduct an electric current. Acids and Bases: An acid is a proton donor and a base is a 24(Bronsted-Lowry concept). Conjugate Acids and Bases: A conjugate base is the species formed when an acid loses a proton. acid1 base1 + proton CH3COOH CH3COO- + H+ acid1 and base1 are a conjugate acid/base pair A conjugate acid is the species formed when a base accepts a proton. base2 + proton acid2 When two processes are combined, the result is an acid/base or neutralization reaction. NH3 + H2O base1 acid2 NH4+ + OHconjugate acid1 conjugate base2 Amphiprotic Solvents: A solvent that can act either as an acid or as a base depending on the solute. ** Water is the classic example. NH3 + H2O base1 acid2 NH4+ + OHc. acid1 c. base2 H2O + HNO2 base1 acid2 H3O+ + NO2c. acid1 c. base2 NH3 + CH3OH base1 acid2 NH4+ + CH3Oc. acid1 c. base2 CH3OH + HNO2 base1 acid2 CH3OH2+ c. acid1 + NO2c.se2 Autoprotolysis: Amphiprotic solvents undergo self ionization to form a pair of ionic species. H2O + H2O H3O+ + OHCH3OH + CH3OH CH3OH2+ + CH3OStrong acid: Reacts with water so completely that no undissociated solute molecules remain. Weak acid: Reacts incompletely with water to give solution that contain significant amounts of both the parent acid and its conjugate base. Strong base: Completely dissociated in water solution Weak base: Incomplete dissociation in water solution Relative Strength  The weakest acid forms the strongest conjugate base.  The tendency of a solvent to accept or donate protons determine the strength of a solute acid or base dissolved in it. H2O + HClO4 CH3COOH + HClO4 base1 acid2 H3O+ + ClO4CH3COOH2+ + ClO4acid1 base2 Chemical Equilibrium  Most of the chemical reactions never result in complete conversion of reactants to products. They proceed to a state of chemical equilibrium in which the ratio of concentrations of reactants and products is constant.  Equilibrium-constant expressions are algebraic equations that describe the concentration relationships that exist among reactants and products at equilibrium.  The position of a chemical equilibrium is independent of the route by which equilibrium is reached.  The Le-Chatelier principle states that the shifts in such a direction as to relieve a stress that is applied to the systemposition of an equilibrium always.  The mass-action effect is a shift in the position of an equilibrium caused by adding one of the reactants or products to a system. Writing Equilibrium Constants wW + xX yY + zZ Where, the capital letters represent the formulas of participating chemical species and the lowercase letters are the small whole numbers (# of moles) required to balance the equation. The equilibrium-constant expression is y z [Y] [Z] K = [W] w [X] x Where, the bracketed terms are molar concentration if the species is a dissolved solute or partial pressure (atm) if the species is a gas. If one of the species is a pure liquid, a pure solid, or the solvent in excess (dilute soln.), no term for this species appear in the equilibrium-constant expression. Equilibrium constant K is a temperature dependent quantity. The Ion-Product Constant for Water Aqueous solutions contain small concentrations of hydronium and hydroxide ions as a consequence of the dissociation reaction. 2H2O H3O+ + OH  Equilibrium constants, [H3O ] [OH ] K = [H2O] 2 The concentration of water in dilute aqueous solution is enormous when compared with the concentration of hydrogen and hydroxide ions. [H2O] can be taken as constant, K[H2O]2 = Kw = [H3O+][OH-] where the new constant is the ion-product constant for water. At 25oC, Kw 1.00 x 10-14 -logKw = - log[H3O]+ - log[OH-] pKw = pH + pOH = 14.00 Solubility-Products Ba2+(aq) + 2IO3-(aq) Ba(IO3)2(s) 2  2 [Ba ] [IO3 ] K = [Ba(IO3)2(S)] K[Ba(IO3)2(s)] = Ksp = [Ba2+][IO3-]2 Where, the new constant, Ksp, is called the solubility-product. The position of this equilibrium is independent of the amount of Ba(IO3)2 as long as some solid is present. Common Ion Affect The common-ion effect is responsible for the reduction in solubility of an ionic precipitate when a soluble compound combining one of the ions of the precipitate is added to the solution in equilibrium with the precipitate. Dissociation Constants for Acids and Bases When a weak acid or a weak base is dissolved in water, partial dissociation occurs,   [H3O ] [NO2 ] HNO2 + H2O H3O+ + NO2- , Ka = [HNO2]   + OH- [NH4 ] [OH ] Kb = [NH3] NH3 + H2O NH4 + , Where Ka and Kb are acid dissociation constant for nitrous acid and base dissociation constant for ammonia respectively. Dissociation Constants for Conjugate Acid/Base Pairs:  NH3 + H2O NH4+ + OH- , [NH4 ] [OH ] NH4+ + H2O NH3 + H3O+ , Ka. Kb = [H3O+ ][OH- ] = Kw K w = K a. K b [NH3]  Kb = [NH3] [H3O ] Ka = [NH4 ]

Chapter 9 Aqueous Solutions and Chemical Equilibria

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