Chem Sample Exam2 - Version 041 Exam 2 Fakhreddine (52395)...

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Version 041 – Exam 2 – Fakhreddine – (52395) 2 K = 8 = [NO 2 ] 2 [N 2 O 2 ] = n 2 x 2 - 0 . 5 n x = n 2 x 2 - n x 2 003 5.0 points In a solution labeled “0.10 M HNO 3 ,” which of the following is CORRECT? 1. [HNO 3 ] = 0.050 M, [H 3 O + ] = 0.050 M, [NO - 3 ] = 0.050 M 2. [H 3 O + ] = 0.10 M, [OH - ] = 1 . 0 × 10 - 7 M 3. [HNO 3 ] = 0.10 M 4. [H 3 O + ] = 0.09 M, [NO - 3 ] = 0.010 M 5. [H 3 O + ] = 0.10 M, [NO - 3 ] = 0.10 M cor- rect Explanation: 004 5.0 points Which of the following is the best chemical de±nition of pure (or neutral) water at any temperature? 1. water that has a pH equal to ZERO 2. water where the concentration of H + is equal to the concentration of OH - correct 3. water that has a pH exactly equal to 7.00 4. water that has been freshly pumped from a well 5. water that has a pH equal to K w 6. water that has a pOH slightly above 7.00 Explanation: You were probably able to narrow this one down to either “water where the concentra- tion . ..” or “water that has a pH exactly equal to 7.00.” The second of these is incorrect because pH varies with temperature since K w varies, but the concentrations of H and OH will still be equal to each other. 005 10.0 points A 0.28 M solution of a weak acid is 3.5% ionized. What is the pH of the solution? 1. 1.46 2. 5.25 3. 0.55 4. 2.01 correct 5. 3.17 Explanation: M =0 . 28 M P =3 . 5% 3 . 5% of the 0 . 28 M is ionized (contributes to pH), so [H + ] = (0 . 28 M) × 3 . 5 100 . 0098 M pH = - log[H + ]= - log(0 . 0098) = 2 . 00877 006 5.0 points The pH of a sample of water from a river is 6.0. A sample of e²uent from a food processing plant has a pH of 4.0. The concentration of hydronium ion in the e²uent is 1. 100 times (100 × ) larger than the river hydronium ion concentration. correct 2. two times (2 × ) larger than the river hydronium ion concentration. 3. four times (4 × ) larger than the river hydronium ion concentration. 4. one and a half times (1 . 5 × ) larger than the river hydronium ion concentration. Explanation: pH of river water = 6.0 pH of plant = 4.0 [H 3 O] = 10 - pH In the river, [H 3 O + ] = 10 - 6
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Version 041 – Exam 2 – Fakhreddine – (52395) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – fnd all choices be±ore answering. 001 10.0 points Suppose the reaction H 2 (g) + I 2 (g) ± ² 2 HI(g) has an equilibrium constant K c = 49 and the initial concentrations o± H 2 ,I 2 and HI are 0.50 M, 0.50 M and 0.00 M, respectively. What is the correct value ±or the fnal concentration o± HI(g)? 1. 0.599 M 2. 0.778 M correct 3. 0.389 M 4. 0.250 M 5. 0.438 M 6. 0.219 M Explanation: K c = 49 [H 2 ] ini =0 . 50 M [I 2 ] ini . 50 M [HI] ini . 0M H 2 (g) + I 2 (g) ± ² 2 HI (g) ini, M 0.5 0.5 0 Δ, M - x - x 2 x eq, M 0 . 5 - x 0 . 5 - x 2 x K c = [HI] 2 [H 2 ] [I 2 ] = 49 (2 x ) 2 (0 . 50 - x ) 2 = 49 2 x 0 . 50 - x =7 2 x =3 . 5 - 7 x 9 x . 5 x . 389 [HI] = 2 x M = 0 . 778 M 002 10.0 points K = 8, ±or the gas phase reaction N 2 O 4 ± ² 2 NO 2 . I± 2 moles o± N 2 O 4 are put into a 1 liter vessel, the number o± moles o± NO 2 at equilib- rium ( n x ) can be calculated ±rom the equation 1. 8= n 2 x 2 - n x 2 correct 2.
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This note was uploaded on 05/19/2011 for the course CHEM 51615 taught by Professor Fatima during the Spring '11 term at University of Texas at Austin.

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Chem Sample Exam2 - Version 041 Exam 2 Fakhreddine (52395)...

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