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Unformatted text preview: Version 191 Exam 4 rowland (53210) 1 This printout should have 30 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points When the reaction 3 NO(g) N 2 O(g) + NO 2 (g) is proceeding under conditions such that 0.015 mol/L of N 2 O is being formed each second, the rate of the overall reaction is ? and the rate of change for NO is ? . 1. 0.015 M s 1 ; 0.005 M s 1 2. 0.030 M s 1 ; 0.005 M s 1 3. 0.015 M s 1 ; +0.045 M s 1 4. none of the other answers is correct 5. 0.015 M s 1 ; 0.045 M s 1 correct Explanation: Notice that three moles of NO are required to make one mole of N 2 O in this reaction, so the rate of disappearance of NO (which has a negative sign) is three times the rate of appearance of N 2 O. 002 10.0 points Express the rate of the following reaction in terms of the [SF 6 ]. 2 CH 2 S + 12 F 2 C 2 F 4 + 4 HF + 2 SF 6 1. rate = 2[SF 6 ] t 2. rate = [SF 6 ] t 3. rate = [SF 6 ] 2 t correct 4. rate = 2[SF 6 ] t 5. rate = [SF 6 ] 2 t Explanation: rate = [CH 2 S] 2 t = [F 2 ] 12 t = [C 2 F 4 ] t = [HF] 4 t = [SF 6 ] 2 t 003 10.0 points What is the molar solubility of CuBr in 0.5 M NaBr? The K sp is 4 . 2 10 8 . 1. 4 . 20 10 7 2. 8 . 40 10 8 correct 3. 4 . 20 10 8 4. 2 . 05 10 4 5. 3 . 48 10 3 Explanation: 004 10.0 points Consider the addition of 0.130 moles of solid NaOH to 1.0 liter of 0.230 M HCl. What will be the pH of the resulting solution? As sume no volume change due to the addition of NaOH. 1. pH = 0.50 2. pH = 0.75 3. pH = 1.00 correct 4. pH = 1.50 5. pH = 2.00 Explanation: 005 10.0 points A buffer solution contains 0.0200 M acetic acid and 0.0200 M sodium acetate. What is the pH after 2.0 millimoles of HCl are added to 1.00 L of this buffer? p K a = 4.75 for acetic Version 191 Exam 4 rowland (53210) 2 acid. 1. 4.66 correct 2. 4.80 3. 4.70 4. 4.84 5. 4.75 Explanation: 006 10.0 points The curve for the titration of formic acid (HCOOH) with NaOH(aq) base is given be low. 2 4 6 8 10 12 14 20 40 60 80 100 120 140 Volume of base (mL) pH Estimate the p K a of formic acid. C a = . 66, C b = 0 . 6204, and the volume of HCOOH is 100 mL. 1. 47 2. None of these 3. 8 . 37 4. 94 5. 3 . 7 correct Explanation: K a = 1 . 8 10 4 C a = 0 . 66 C b = 0 . 6204 V HCOOH = 100 mL 2 4 6 8 10 12 14 20 40 60 80 100 120 140 Volume of base (mL) pH (94,8 . 37) (47,3 . 7) The equivalence point of this titration is when the curve is at an inflection point (nearly vertical); i.e. , at a volume of 94 mL . The pH at the equivalence point of this titration is 8 . 37 pH ....
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 Spring '10
 Rowland
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