Exam 1-solutions

Exam 1-solutions - Version 573 Exam 1 Laude (52390) 1 This...

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Unformatted text preview: Version 573 Exam 1 Laude (52390) 1 This print-out should have 29 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 6.0 points What would be the pH of a solution of hypo- bromous acid (HOBr) prepared by dissolving 9.7 grams of the acid in 20 mL of pure wa- ter (H 2 O)? The Ka of hypobromous acid is 2 10 9 1. 1 2. 4 correct 3. 10 4. 13 5. 6 Explanation: 9 . 7 g HOBr 1 mol 97 g = 0 . 1 mol HOBr . 1 mol HOBr . 02 L H 2 O = 5 M HOBr [H + ] = (K a C a ) 1 / 2 = (2 10 9 5) 1 / 2 = (10 8 ) 1 / 2 = 10 4 pH =- log[H + ] =- log(10 4 ) = 4 002 6.0 points Rank following salts from most to least solu- ble: BiI K sp = 7 . 7 10 19 Cd 3 (AsO 4 ) 2 K sp = 2 . 2 10 33 AlPO 4 K sp = 9 . 8 10 21 CaSO 4 K sp = 4 . 9 10 5 1. AlPO 4 < BiI < Cd 3 (AsO 4 ) 2 < CaSO 4 correct 2. CaSO 4 < AlPO 4 < BiI < Cd 3 (AsO 4 ) 2 3. Cd 3 (AsO 4 ) 2 < CaSO 4 < AlPO 4 < BiI 4. BiI < Cd 3 (AsO 4 ) 2 < CaSO 4 < AlPO 4 Explanation: Molar solubility can be approximated by taking the n th root of the K sp where n is the number of ions in the salt. Doing so results in approximate molar solubilities of 10 10 , 10 7 , 10 11 and 10 3 for bismuth iodide, cadmium arsenate, aluminum phosphate and calcium sulfate, respectively. Arranging these from least to greatest produces: AlPO 4 < BiI < Cd 3 (AsO 4 ) 2 < CaSO 4 . 003 6.0 points Determine the molar solubility of calcium chloride (CaCl 2 ) if K sp = 2 . 5 10 2 . 1. 4 M correct 2. 1 M 3. 10 M 4. 0.005 M 5. 0.1 M Explanation: The equation for K sp = x (2 x ) 2 = 4 x 3 x = parenleftbigg 1 4 K sp parenrightbigg 1 / 3 . Plugging in numbers gives you 3.97 M, or about 4 M. 004 6.0 points What would be the pH of a 0.25 M solution of phenylamine (C 6 H 5 NH 2 ) at room temper- ature? The K b of phenylamine is 4 10 10 . 1. 9 correct 2. 5 3. 1 4. 13 5. 10.5 Explanation: [OH ] = (K b C b ) 1 / 2 = (4 10 10 . 25) 1 / 2 = (10 10 ) 1 / 2 = 10 5 pOH =- log[OH ] =- log(10 5 ) = 5 pH = pK w- pOH = 14- 5 = 9 Version 573 Exam 1 Laude (52390) 2 005 6.0 points Consider the following exothermic reaction: CaO( s ) + CO 2 ( g ) CaCO 3 ( s ) In response to a decrease in temperature, the system would: 1. not change 2. not enough information 3. shift right correct 4. shift left Explanation: Decreasing the temperature of an exother- mic reaction can, according to the Le Chate- lier principle, be thought of as removing some of the products (on the right) and the system would respond by shifting right. 006 6.0 points Consider the reaction, Na + ( aq ) + Cl ( aq ) NaCl( aq ) The equilibrium constant, K , is 2. If the concentrations of Na + , Cl and NaCl are 2, 2 and 10 M, respectively, which of the following would occur?...
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This note was uploaded on 05/04/2009 for the course CH 52390 taught by Professor Laude during the Spring '09 term at SUNY Adirondack.

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Exam 1-solutions - Version 573 Exam 1 Laude (52390) 1 This...

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