Chemistry HW 6 - ekk86 hw06 Holcombe (53570) This print-out...

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ekk86 – hw06 – Holcombe – (53570) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. PLEASE NOTE: Due to the tolerances on numerical problems (your answer must be within ONE PERCENT oF the correct answer unless otherwise noted), iF a problem requires the quadratic Formula to fnd the solution, DO NOT make any assumptions (i.e. USE THE QUADRATIC ±ORMULA). Also, be sure to enter excess signifcant fgures to assure that you are not penalized For rounding. 001 10.0 points Solution A contains HCl and has an H + con- centration oF 10 - 3 M. Solution B contains CH 3 COOH and has an H + concentration oF 10 - 5 M. Which solution is more acidic and which solution has a greater pH? 1. Solution A is more acidic, but Solution B has a greater pH. correct 2. Both solutions have identical acidities and pH. 3. Solution B is more acidic, but Solution A has a greater pH. 4. Solution A is more acidic and has a greater pH. 5. Solution B is more acidic and has a greater pH. Explanation: [H + ] A = 10 - 3 M [H + ] B = 10 - 5 M pH = - log[H + ] The solutions have di²erent concentrations oF H + . ThereFore, they will have di²erent acidities and pH. The more concentrated will be more acidic and have a lower pH. 002 10.0 points The buildup oF lactic acid in muscles causes pain during extreme physical exertion. The K a For lactic acid (C 2 H 5 OCOOH) is 8 . 4 × 10 - 4 . Calculate the pH oF a 0 . 06 M solution oF lactic acid. 1. 6.348 2. 2.174 correct 3. 2.149 4. 3.533 5. 11.851 6. 2.043 7. 2.297 8. 1.926 Explanation: K a =8 . 4 × 10 - 4 [C 2 H 5 OCOOH] = 0 . 06 You MUST use the quadratic Formula to solve this one. IF you use the approximation, your answer will be more than 5% o². C 2 H 5 OCOOH + H 2 O ± ² Initial 0.06 ±inal 0 . 06 - x C 2 H 5 OCOO - +H 3 O + Initial -- ±inal xx K a = ± C 2 H 5 OCOO - ²± H 3 O + ² [C 2 H 5 OCOOH] = x 2 0 . 06 - x . 4 × 10 - 4 x 2 +8 . 4 × 10 - 4 x - 5 . 04 × 10 - 5 =0 To solve the quadratic equation, x = - b ± b 2 - 4 ac 2 a Since b 2 - 4 = ( - 8 . 4 × 10 - 4 ) 2 - 4 (1) ( - 5 . 04 × 10 - 5 ) =2 . 02 × 10 - 4 , then
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ekk86 – hw06 – Holcombe – (53570) 2 x = ( - 8 . 4 × 10 - 4 ) ± 2 . 02 × 10 - 4 2 (1) = (0 . 00669 , - 0 . 00753) , x = ± H 3 O + ² =0 . 00669, so pH = - log ± H 3 O + ² = - log(0 . 00669) =2 . 174 003 10.0 points The pH of 0 . 1 M HClO 2 (chlorous acid) aqueous solution was measured to be 1 . 2. What is the value of p K a for chlorous acid? 1. 1.20 2. 0.96 correct 3. 0.11 4. 1.40 5. 3.91 6. 2.57 Explanation: M . 1 M pH = 1 . 2 Analyzing the reaction with molarities, HClO 2 +H 2 O ± ² H 3 O + + ClO - 2 0 . 1 - 00 - x - xx 0 . 1 - x - [H 3 O + ] = [ClO - 2 ] = 10 - pH = 10 - 1 . 2 . 0630957 mol / L The K a is K a = [H 3 O + ][ClO - 2 ] [HClO 2 ] = (0 . 0630957) 2 0 . 1 - 0 . 0630957 . 107876 and the p K a is p K a = - log(0 . 107876) = 0 . 967077 .
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Chemistry HW 6 - ekk86 hw06 Holcombe (53570) This print-out...

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