Exam 1 (2007)

Exam 1 (2007) - University of Houston BCHS 3304 Exam I....

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University of Houston BCHS 3304 Exam I. Instructor: Dr. Briggs, Feb. 8, 2007 Printed Name_____ANSWER KEY ________ Answer all questions; show all work. Multiple choice – Circle the single letter (i.e. a., b., c., d., or e.) of the most correct answer on the EXAM, then mark it on the Scantron sheet with a #2 pencil. Mark BOTH the exam AND the Scantron sheet!! 1). What is a Brønsted base? (2 pts) a. A molecule that can accept a proton b. A molecule that can form a hydrogen-bond c. A molecule that has a net charge d. A molecule that can donate a proton e. A molecule that cannot form a hydrogen-bond 2). How many Å are there in 32.1 m? (2 pts) a. 32.1x10 -10 Å b. 3.21x10 -10 Å c. 0.321x10 -10 Å d. 32.1x10 10 Å e. 3.21x10 10 Å 1 Å = 1x10 -10 m; conversion factor = 1nm/1x10 -10 m nm 10 1 . 32 m 1 . 32 m 10 1 Å 1 ; m 10 1 Å 1 1 10 10 10 x x x x = = 32.1 m = 32.1x10 10 Å 3). How many femtoseconds are there in 23.1 ms? (2 pts) a. 2.31x10 -13 fs b. 23.1x10 -9 fs c. 2.31x10 15 fs d. 23.1x10 9 fs e. 2.31x10 13 fs 1 fs (femtosecond) = 1x10 -15 s; 1 ms (millisecond) = 1x10 -3 s fs x s x fs x ms s x x ms 13 15 3 10 31 . 2 10 1 1 10 1 1 . 23 = 4). How many kJ/mol are there in 5.67 kcal/mol? (2 pts) a. 1.36 kJ/mol b. 1,360 kJ/mol c. 23.7 kJ/mol d. 0.0237 kJ/mol e. 23,700 kJ/mol 1 kcal/mol = 4.184 kJ/mol mol kJ mol kcal mol kJ x mol kcal / 7 . 23 / 1 / 184 . 4 / 67 . 5 =
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5). If the enthalpy change of a process is positive and the entropy change is negative, the free energy change is: (2 pts) a. spontaneous b. non-spontaneous c. zero d. temperature dependent e. exergonic See Table 1-3 in the book Δ G = Δ H – T Δ S = (+) – T(–) = +, non-spontaneous at all temperatures 6). What is the pH of a 0.005 M HCl solution? (Hydrochloric acid completely dissociates in H 2 O) (2 pts) a. 7.005 b. 2.3 c. 5.3 d. 0.5 e. 0.005 pH = –log[H+], [H+]=0.005M, pH=2.3 7). What is the pH of a 0.00005 M NaOH solution? (Sodium hydroxide completely dissociates in H 2 O) (2 pts) a. 7.0 b. 11.7 c. 5.0 d. 22.3 e. 9.7 pH = –log[H+], Kw=[H+][HO-]=1.0x10 -14 =[H+](0.00005); [H+]=2x10 -10 pH=-log(2x10 -10 ), pH=9.7 8). The enthalpy change ( Δ H) for a reaction is –6.5 kJ/mol and the entropy change ( Δ S) is 4.5 cal/mol/K, what is the free energy ( Δ G) for the reaction in kJ/mol at 298K? (2 pts) a. –12.11 kJ/mol b. -6.50 kJ/mol c. –0.89 kJ/mol d. 18.83 kJ/mol e. Is not spontaneous Δ G = Δ H – T Δ S = –6.5 kJ/mol – 298K(4.5 cal/mol/K*4.184 kJ/kcal / (1000 J/kJ)) = –12.11 kJ/mol
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9). What is the pH of a 1L solution that has 250mL of 0.5 M NaOH? (2 pts) a. 13.8 b. 13.1 c. 7.0 d. 0.5 e. neutral pH = –log [H+] [HO-] = (0.250L)(0.5M)/1L = 0.125M; [H+] = 1x10 -14 /[HO-] = 1x10 -14 M 2 /0.125M = 8.0x10 -14 M pH = –log [H+] = –log (8.0x10 -14 ) = 13.1 10). Calculate the pH of a 1L solution containing 100mL of 2M acetic acid and 300mL of 3M sodium acetate? The pKa of acetic acid is 4.76. (2 pts) a. 7.00 b. 5.41 c. 4.46 d. 4.76 e. 11.76 Acetic acid: (0.10L)(2M)/1L = 0.20M Acetate: (0.30L)(3M)/1L) = 0.90M pH = pKa + log([acetate]/[acetic acid]) = 4.76 + log(0.90/0.20) = 4.76 + (0.65) = 5.41
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Exam 1 (2007) - University of Houston BCHS 3304 Exam I....

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