Exam 1 (2006)

# Exam 1 (2006) - University of Houston BCHS 3304 Exam I....

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University of Houston BCHS 3304 Exam I. Instructor: Dr. Briggs, Feb. 9, 2006 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, then mark it on the Scantron sheet with a #2 pencil. Mark BOTH the exam AND the Scantron sheet. 1). What is a Brønsted acid? (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 nm are there in 32.1 m? (2 pts) a. 32.1x10 -9 nm b. 3.21x10 -9 nm c. 0.321x10 -9 nm d. 32.1x10 9 nm e. 3.21x10 9 nm 1 nm = 1x10 -9 m; conversion factor = 1nm/1x10 -9 m nm 10 1 . 32 m 1 . 32 m 10 1 nm 1 ; m 10 1 nm 1 1 9 9 9 x x x x = = 32.1 m = 32.1x10 9 nm 3). How many picoseconds are there in 23.1 ms? (2 pts) a. 2.31x10 -15 ps b. 2.31x10 -9 ps c. 2.31x10 9 ps d. 23.1x10 9 ps e. 2.31x10 15 ps 1 ps (picosecond) = 1x10 -12 s; 1 ms (millisecond) = 1x10 -3 s ps x s x ps x ms s x x ms 9 12 3 10 1 . 23 10 1 1 10 1 1 . 23 = 4). How many kJ/mol are there in 2.31 kcal/mol? (2 pts) a. 9.67 kJ/mol b. 9.67 kcal/mol c. 0.1034 kJ/mol d. 0.1034 kcal/mol e. 2.31 kJ/mol 1 kcal/mol = 4.184 kJ/mol mol kJ mol kcal mol kJ x mol kcal / 67 . 9 / 1 / 184 . 4 / 31 . 2 =

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5). If the enthalpy change of a process is negative and the entropy change is positive, the free energy change is: (2 pts) a. spontaneous b. non-spontaneous c. zero d. temperature independent e. catalyzed by an enzyme See Table 1-3 in the book Δ G = Δ H – T Δ S = (–) – T(+) = – 6). What is the pH of a 0.05 M HCl solution? (Hydrochloric acid completely dissociates in H 2 O) (2 pts) a. 7.05 b. 3.0 c. 0.30 d. 1.3 e. 0.5 pH = –log[H+], [H+]=0.05M, pH=1.3 7). What is the pH of a 0.005 M NaOH solution? (Sodium hydroxide completely dissociates in H 2 O) (2 pts) a. 7.0 b. 11.7 c. 1.27 d. 1.3 e. 12.7 pH = –log[H+], Kw=[H+][HO-]=1.0x10 -14 =[H+](0.005); [H+]=2x10 -12 pH=-log(2x10 -12 ), pH=11.7 8). The enthalpy change ( Δ H) for a reaction is –3.5 kJ/mol and the entropy change ( Δ S) is 2.5 cal/mol/K, what is the free energy ( Δ G) for the reaction in kJ/mol at 298K? (2 pts) a. –6.62 kJ/mol b. 6.62 kJ/mol c. –0.38 kJ/mol d. –3.12 kJ/mol e. Is not spontaneous Δ G = Δ H – T Δ S = –3.5 kJ/mol – 298K(2.5 cal/mol/K*4.184 kJ/kcal / (1000 J/kJ)) = –6.62 kJ/mol
9). What is the pH of a 1L solution that has 600mL of 1M NaOH? (2 pts) a. 13.8 b. 14.3 c. 7.0 d. 0.6 e. neutral pH = –log [H+] [HO-] = (0.6L)(1M)/1L = 0.6M; [H+] = 1x10 -14 /[HO-] = 1x10 -14 M 2 /0.6M = 1.67x10 -14 M pH = –log [H+] = –log (1.67x10 -14 ) = 13.8 10). Calculate the pH of a 1L solution containing 100mL of 3M acetic acid and 150mL of 1M sodium acetate? The pKa of acetic acid is 4.76. (2 pts) a. 7.00 b. 4.24 c. 4.46 d. 4.06 e. 3.94 Acetic acid: (0.10L)(3M)/1L = 0.30M Acetate: (0.15L)(1M)/1L) = 0.15M pH = pKa + log([acetate]/[acetic acid]) = 4.76 + log(0.15/0.30) = 4.76 + (–0.30) = 4.46

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## This note was uploaded on 12/02/2011 for the course BCHS 3304 taught by Professor Johnson during the Spring '08 term at University of Houston.

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Exam 1 (2006) - University of Houston BCHS 3304 Exam I....

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