Final - Version 334 Final Sutclie(52410 This print-out...

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Version 334 – Final – Sutcliffe – (52410) 1 This print-out should have 37 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Calculate the standard reaction enthalpy for the reaction of calcite with hydrochloric acid CaCO 3 (s) + 2 HCl(aq) -→ CaCl 2 (aq) + H 2 O( ) + CO 2 (g) The standard enthalpies of formation are: for CaCl 2 (aq) : - 877 . 1 kJ / mol; for H 2 O( ) : - 285 . 83 kJ / mol; for CO 2 (g) : - 393 . 51 kJ / mol; for CaCO 3 (s) : - 1206 . 9 kJ / mol; and for HCl(aq) : - 167 . 16 kJ / mol. 1. - 98 . 8 kJ/mol 2. - 15 . 2 kJ/mol correct 3. - 38 . 2 kJ/mol 4. - 116 kJ/mol 5. - 72 . 7 kJ/mol 6. - 215 kJ/mol 7. - 165 kJ/mol Explanation: We use Hess’ Law: Δ H = summationdisplay n Δ H j , prod - summationdisplay n Δ H j , reac = Δ H f , CaCl 2 (aq) + Δ H f , H 2 O( ) + Δ H f , CO 2 (g) - bracketleftBig Δ H f , CaCO 3 (s) +2 parenleftBig Δ H f , HCl(aq) parenrightBigbracketrightBig = - 877 . 1 kJ / mol + ( - 285 . 83 kJ / mol) + ( - 393 . 51 kJ / mol) - bracketleftBig - 1206 . 9 kJ / mol + 2 ( - 167 . 16 kJ / mol) bracketrightBig = - 15 . 22 kJ / mol . 002 10.0 points Consider the reaction 2 HgO(s) 2 Hg( ) + O 2 (g) . What is the form of the equilibrium constant K c for the reaction? 1. K c = [O 2 ] correct 2. K c = [Hg] 2 [O 2 ] [HgO] 2 3. K c = [Hg] 2 [O 2 ] 4. None of the other answers is correct. 5. K c = [O 2 ] [HgO] 2 Explanation: Solids and liquids are not included in the K expression. 003 10.0 points Consider the titration of equal volumes of 0.1 M HCl and 0.1 M HC 2 H 3 O 2 with 0.1 M NaOH. Which of the following would be the same for both titrations? 1. the pH at the halfway point 2. Two of the other answers are correct. 3. the pH at the equivalence point 4. the volume of NaOH added to reach the equivalence point correct 5. the initial pH Explanation: Both HCl and CH 2 C 3 O 2 H 2 are monoprotic acids and so if the volume concentrations are identical, the amounts of replaceable H + in both solutions are identical. 004 10.0 points The molar heat capacity of some molecule X( ) is 10 cal/K · mol, its heat of vaporization
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Version 334 – Final – Sutcliffe – (52410) 2 is 5000 cal/mol and its boiling point is 75 C. For the conversion of one mol of X(g) at 75 C to one mol of X( ) at 60 C, 1. 4850 cal of heat are released by X. 2. 5150 cal of heat are absorbed by X. 3. 4850 cal of heat are absorbed by X. 4. 5150 cal of heat are released by X. cor- rect 5. 150 cal of heat are released by X. Explanation: 005 10.0 points The solubility product constant of PbCl 2 is 1 . 7 × 10 5 . What is the maximum concentra- tion of Pb 2+ that can be in ocean water that contains 0.0500 M NaCl? 1. 6 . 8 × 10 3 M correct 2. 3 . 4 × 10 3 M 3. 8 . 5 × 10 7 M 4. 1 . 7 × 10 3 M 5. 4 . 2 × 10 8 M Explanation: K sp of PbCl 2 = 1.7 × 10 5 PbCl 2 Pb 2+ + 2FCl K sp = [Pb 2+ ] [Cl ] 2 1 . 7 × 10 5 = [Pb 2+ ] (0 . 05) 2 [Pb 2+ ] = 0 . 0068 006 10.0 points Note: Ionization constant is the same thing as K a . What is the concentration of hydroxide ion in a 0.10 M solution of NaCN? The ionization constant of the weak acid HCN is 4.0 × 10 10 .
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