Exam 3A Fetzer Gislason. Name (print)

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1 Fetzer Gislason, December 1, 2003 Name (print) TA Directions: There are 25 multiple-choice 4 points each. Record these answers on your scantron sheet. Total possible score is 100 points. You must hand in this page (with your name) and your scantron before leaving. Answers will be posted on our web page tomorrow. 1) Tear off the last page; this contains a periodic table, constants and. formulas 2) Work out the multiple-choice problems and transfer your answers to the scantron sheet. 3) When finished, tear off this page and give it to your TA. 4) Put your scantron sheet in the box marked form A. 5) If you are not finished when I call time, you are to insert your scantron sheet into your exam and pass both to the left aisle to be collected by the TAs. Scantron sheet: 1) Print name (last name, first name) and fill in the corresponding bubbles. 2) Sign your name where it says signature. 3) On bottom right where it says course number and instructor, write in: Chem112, TA s name, and Form A.

2 1) Which one of the following could not be both a Bronsted-Lowry acid and base? 2 a) NO 2 b) NH 3 c) HPO 3 d) H 2 O e) HClO 3 2) The initial ph in a titration curve is 3.4 and the ph at the equivalence point is 8.7 You are titrating with. a) a strong base with a strong acid b) a strong acid with a strong base c) a weak acid with a strong base d) a weak base with a strong acid 3) Consider the following reaction at equilibrium: 2 NH 3 (g) N 2 (g) + 3 H 2 (g) H = kj This conditions that will favor formation of products are the a) increase of temperature and decrease of pressure b) increase of both temperature and pressure c) decrease of both temperature and pressure d) decrease of temperature and increase of pressure Questions 4-5 use the following information: 3 Al 2 Cl 6 (g) 2 Al 3 Cl 9 (g) K = at 454 K. 4) When atm Al 2 Cl 6 and atm of Al 3 Cl 9 are placed in a closed container at 454 K, a) the reaction will proceed from right to left because Q < K b) the reaction will proceed from left to right because Q > K c) the reaction will proceed from left to right because Q < K d) the reaction will proceed from right to left because Q > K 5) When the temperature of this reaction is decreased to 300 K, the equilibrium constant is found to increase to a) The reaction must be endothermic b) The reaction must be exothermic c) The equilibrium constant cannot change. d) The equilibrium constant should have decreased. 6) At equilibrium, a) all chemical processes have ceased. b) both the rate of the forward reaction equals that of the reverse and the rate constant for the forward reaction equals that of the reverse. c) the rate constant for the forward reaction equals that of the reverse. d) the rate of the forward reaction equals the rate of the reverse reaction. e) none of the above 7) Lactic acid, HC 3 H 5 O 3, is a monoprotic acid. A 0.20 M solution of lactic acid has a ph of Calculate Ka. HC 3 H 5 O 3 (aq) + H 2 O(l) H 3 O + (aq) + C 3 H 5 O 3 (aq) a) b) c) d) e)

3 8) Which of the following is/are strong acids? (i) HClO 3 (ii) HNO 2 (iii) HClO (iv) H 2 SO 3 (v) HI a) all of these are strong acids b) only (ii), (iii), and (iv) c) only (i) and (iii) d) only (i) and (iv) e) only (i) and (v) 9) Calculate ph of M Mg(OH) 2. a) 4.55 b) 4.25 c) 9.45 d) 9.75 e) ) Which one of the following statements is incorrect? a) exothermic reactions shift the equilibrium to the left with increasing temperature. b) Adding reactants shifts the equilibrium to the right. c) Adding products shifts the equilibrium to the left. d) Removing a product shifts the equilibrium to the right. e) Adding catalyst shifts the equilibrium to the right 11) What is the ratio of [HCO 3 ] to [H 2 CO 3 ] in blood at ph 7.40 and Ka = ? a) b) c) 11 d) e) ) If we compare a N=O double bond with a N O single bond, we conclude that the N=O bond has bond enthalpy and bond length than the N O bond. a) Greater, longer b) greater, shorter c) lower, longer d) Lower, shorter e) lower, equal 13) A molecule that has three bonding domains and one lone pair (nonbonding domain) on its central atom has a electronic geometry and a molecular geometry. a) trigonal pyramid, trigonal planar b) trigonal planar, angular c) tetrahedral, pyramidal d) tetrahedral, trigonal pyramidal e) tetrahedral, trigonal planar 2

4 14) A flask is charged with 1.50 atm of N 2 O 4 gas and 1.00 atm of NO 2 gas at 298 K. The equilibrium reaction is: N 2 O 4 (g) 2 NO 2 (g). After equilibrium is reached, the partial pressure of NO 2 is atm. The equilibrium partial pressure of N 2 O 4 is atm and K =. N 2 O 4 (g) 2 NO 2 (g) a) 1.26, 1.07 b) 1.74, c) 1.01, d) 1.26, 2.10 e) 1.74, ) The ph of a M NaF solution is. a) b) c) d) e) ) In the reaction, HCO 3 (aq) + NH 4 + (aq) NH 3 (aq) + H 2 CO 3 (aq), a) HCO 3 and NH 4 + are both acids b) HCO 3 and H 2 CO 3 are both acids c) H 2 CO 3 is an acid and NH 4 + is a base d) NH 3 and NH 4 + are both bases e) NH 4 + is an acid and HCO 3 is a base Questions 17-18: You are going to titrate 25.0 ml of M HCO 3 with NaOH. The equation is: HCO 3 (aq) + H 2 O(l) H 3 O + (aq) + CO 3 2 (aq) Ka = ) The ph at the half-equivalence point in the titration is a) b) 6.42 c) 7.00 d) 8.75 e) ) The volume of M NaOH needed to neutralize this acid is ml. a) 26.4 b) 25.0 c) 22.4 d) 240 e) ) A g sample of a monoprotic acid (molar mass = g/mol) is dissolved in water and titrated with NaOH. It requires ml NaOH to neutralize this acid. The molarity of the NaOH solution is M. a) 3.94 b) c) 3.77 d) e)

5 Questions use the following information: A buffer solution contains M HClO and M ClO. HClO(aq) + H 2 O(l) H 3 O + (aq) + ClO - (aq) 20) Calculate the ph of the solution. a) 7.58 b) 6.42 c) 7.48 d) 6.53 e) ) Addition of a small amount of NaOH will cause the ph of the buffer to ; addition of a small amount of HCl will cause the ph of the buffer to. a) increase, decrease b) decrease, increase c) neither will affect the ph 22) The bonding in the compounds N 2 O, K 2 O, and N 2 is a) pure covalent, polar covalent, ionic b) ionic, polar covalent, pure covalent c) polar covalent, ionic, pure covalent d) polar covalent, polar covalent, pure covalent 23) The molecule (IF 4 ) has bonding domains and lone pairs. a) 5, 1 b) 4, 0 c) 5, 0 d) 4, 2 e) 4,1 Questions 24-25: A 25.0-mL sample of 0.20 M HClO 3 is titrated with 0.24 M NaOH 24) The ph after the addition of mL NaOH is a) 2.58 b) c) 1.13 d) e) ) The ph at the equivalence point of the titration is. a) less than 7 b) 7 c) greater than 7 d) 0 e) 14 4

6 ph = pka + log base acid (Ka)( Kb) = Kw b b 2 4 ac 2a x = ± Formulas and Constants ph = -log [H 3 O + ] poh = -log [OH ] ph + poh = 14 [H 3 O + ][OH ] = = K W = [H 3 O + ] = 10 ph [OH ] = 10 poh 5