the “second S”) indicates the point of maximum buffering of the second buffering zone where [HA-] / [A2-] = 1. The middle of the “second S” is the second equivalence point where [HA-] = 0. The top part of the “second S” levels off at the pH of the base solution. 22. Solubility Product (Ksp) Example 1: Co(OH)2(s) Co2+ + 2OH- Ksp = [Co2+][]2 (don’t forget – concentration of is twice the solubility) Example 2: Solubility of Ag2SO4 is 0.016 mol L-1 (5.0 g L-1). Find the Ksp of Ag2SO4. (Answer: Ksp = 1.5 × 10-5) 23. Ion product (Qi) – equivalent to the “reaction quotient” Qi < Ksp all ions in solution; more will dissolve Qi = Ksp equilibrium – solution is saturated Qi > Ksp precipitation will occur until Qi = Ksp 24. Solubility of any salt which contains a basic anion is influenced by pH: Example: Consider a solution which is 1 M in each of Fe3+ and H+. Will Fe(OH)3 precipitate? Answer: NO! Fe(OH)3 Fe3+ + 3 Qi = [Fe3+][] If [H+] = 1 M, then [] = 10-14 Qi = (1) (10-14)3 = 10-42 Since Ksp for Fe(OH)3 = 3 × 10-39; precipitation does not occur. However, what if [H+] = 10-5? Then [] = 10-9 Qi = (1) (10-9)3 = 10-27 Since Qi > Ksp; Fe(OH)3 will precipitate! Free Response Questions 2007 #1 1. HF(aq) + H2O(l) H3O+(aq) + F-(aq) Ka = 7.2 × 10-4 Hydrofluoric acid, HF(aq), dissociates in water as represented by the equation above.
E) The degree of dissociation of Na2SO4 in solution is significantly greater than that of NaCl. 2008 #44 Cl2(g) + 2 I-(aq) 2 Cl-(aq) + I2(aq) Which of the following best accounts for the fact that a galvanic cell based on the reaction represented above will generate electricity? A) Cl2 can easily lose two electrons. B) Cl2 is a stronger oxidizing than I2 (48%) C) I have more electrons than do atoms of Cl D) I- is a more stable species than I2 E) I2(s) is more soluble than Cl2(g) 2008 #74 An electric current of 1.00 ampere is passed through an aqueous solution of Ni(NO3)2. How long will it take to plate out exactly 1.00 mol of nickel metal, assuming 100 percent current efficiency? (1 faraday = 96,500 coulombs = 6.02 x 1023 electrons) A) 386,000 sec B) 193,000 sec (24%) C) 96,500 sec D) 48,200 sec E) 24,100 sec AP Chemistry Concepts - THERMODYNAMICS 1. ∆H0 rxn = ∑ ∆ Hf 0Products - ∑∆ Hf0 Reactants = ∑ Bond Energy Reactants - ∑ Bond energy Products ∆Hrxn - exothermic ∆Hrxn + endothermic 2. ∆S0 rxn = ∑ Sf0 Products - ∑ Sf0 Reactants ∆S0rxn - ordered ∆S0rxn + disordered 3. ∆G0 rxn = - T ∆S 0rxn ∆G0rxn - spontaneous ∆G0rxn + nonspontaneous
For the reaction of ethylene represented above, H is - 1,323 kJ. What is the value of H if the combustion produced liquid water H2O(l), rather than water vapor H2O(g)? (H for the phase change H2O(g) --> H2O(l) is -44 kJ A) -1,235 kJ B) -1,279 kJ C) -1,323 kJ D) -1,367 kJ E) -1,411 kJ (31%) 2002 #25 3 C2H2(g) C6H6(g) What is the standard enthalpy change, ΔHo, for the reaction represented above? (ΔHof of C2H2(g) is 230 kJ mol-1; ΔHof of C6H6(g) is 83 kJ mol-1.) A) -607 kJ (66%) B) -147 kJ C) -19 kJ D) +19 kJ E) +773 kJ 1999 #22 Of the following reactions, involves the largest decrease in entropy? A) CaCO3(s) ---> CaO(s) + CO2(g) B) 2 CO(g) + O2(g) ---> 2 CO2 C) Pb(NO3)3 + 2 KI ---> PbI2 + 2 KNO3 D) C3H8 + O2 ---> 3 CO2 + 4 H2O E) 4 La + 3 O2 ---> 2 La2O3 (68%) 2002 #41 When solid NH4SCN is mixed with solid Ba(OH)2 in a closed container, the temperature drops and a gas is produced. Which of the following indicates the correct signs for ΔG, ΔH, and ΔS for the process? ΔG ΔH ΔS A) - - - B) - + - C) - + + (43%) D) + - + E) + - - 2002 #73 X(s) X(l)
Which of the following is true for any substance undergoing the process represented above at its normal melting point? A) ΔS < 0 B) ΔH = 0 C) ΔH = TΔG D) TΔS = 0 E) ΔH = TΔS(34%) AP Chemistry Concepts - ATOMIC THEORY, BONDING AND INTERMOLECULAR FORCES 1. Quantum Numbers ,electron configurations, Hund’s rule, orbital diagrams 2. bonds 3. Covalent bonds, Lewis structures, geometric shapes, bond polarity, molecular polarity, resonance, hybridization, London dispersion forces (LDF), inter vs. intramolecular forces 4. Trends of the periodic - a) size for atoms b) size of ions, c) IE, EA, EN 5. Effective nuclear charge (Zeff ) increases as more protons to same energy Zeff is a comparison tool. 6. Effective nuclear charge (Zeff ) decreases as more shielding electrons are present. 7. Intermolecular Forces (IMF) are between molecules and help explain differences in FP, BP, solids, liquids, gases, and solubilities. ion – ion dipole – dipole with H bonding dipole – dipole dispersion forces ( LDF ) 8. When students talk about EN differences they are talking about bonds (within a molecule) , we need them to talk about IMF (between molecules ) 9. Students often talk about atoms “wanting to gain/lose electrons”, being happy, Full, rather than having a stable octet, complete energy level. Free Response Questions 1996 # 9
A) C8H18(l) and H2O(l) B) CH3CH2CH2OH(l) and H2O(l) C) CH3CH2CH2OH(l) and C8H18(l) D) C6H14(l) and C8H18(l) (33%) E) H2SO4(l) and H2O(l) AP Chemistry Concept List – CONCENTRATION OF SOLUTIONS / COLLIGATIVE PROPERTIES 1. Molarity M = mole of solute/ L of solution 2. molality m = mole of solute / Kg of solvent 3. % by volume = volume of solute / volume of solution 4. % by weight = weight of solute / total weight of solution 5. mole fraction = xa = mole of a moles in solution Colligative Properties 1. ∆ FP ↓ = (kf ) ( m ) ( i ) freezing depression 2. ∆ BP ↑ = ( kb ) (m ) ( i ) boiling point elevation 3. ∏ = ( M ) ( R ) ( T ) ( i ) osmotic pressure 4. Vapor Pressure Lowering = VPL = (x solvent) VP pure solvent The main use of colligative properties is to find the molecular weight of an unknown compound, thus it is related to problems in earlier chapters about empirical or molecular formulas. i = Van’t Hoff factor for organic solutes nonelectrolytes i = 1 for electrolytes i = 2,3,4… NaCl i = 2 AlCl3 i = 4