H05 Mccord - patino(mp25752 – H05 Acid/Base Equilibrium...

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Unformatted text preview: patino (mp25752) – H05: Acid/Base Equilibrium – McCord – (53215) 1 This print-out should have 28 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Which of the following is true in pure water at any temperature? 1. pH = 7.0 or greater than 7.0 2. pH = 7.0 3. K w decreases with increasing tempera- ture. 4. [H 3 O + ][OH − ] = 1.0 × 10 − 14 5. [H 3 O + ] = [OH − ] correct Explanation: K w is shown to INCREASE with increas- ing temperature. pH = 7 is only true when water is at 24 ◦ C. [H 3 O + ][OH − ] = K w , which increases with temperature. At high temperatures pH can be less than 7. Thus [H 3 O + ] = [OH − ] is the only case that is true. 002 10.0 points What is [H 3 O + ] when [OH − ] = 3 . 3 × 10 − 9 M? 1. 3 . 3 × 10 − 9 M 2. 3 . × 10 − 6 M correct 3. 3 . 3 × 10 − 5 M 4. 1 . × 10 − 7 M 5. 6 . 6 × 10 − 5 M Explanation: [OH − ] = 3 . 3 × 10 − 9 M K w = [H 3 O + ][OH − ] = 1 × 10 14 [H 3 O + ] = K w [OH − ] = 1 . × 10 14 3 . 3 × 10 − 9 = 3 . × 10 − 6 M 003 10.0 points What is [OH − ] when [H 3 O + ] = 8 . 2 × 10 − 5 M? 1. 1 . 2 × 10 − 10 M correct 2. 8 . 2 × 10 − 5 M 3. 6 . 3 × 10 − 9 M 4. 1 . 2 × 10 − 4 M 5. 1 . × 10 − 7 M Explanation: [H 3 O + ] = 8 . 2 × 10 − 5 M K w = [OH − ][H 3 O + ] = 1 . × 10 14 [OH − ] = K w [H 3 O + ] = 1 . × 10 14 8 . 2 × 10 − 5 = 1 . 2 × 10 − 10 M 004 10.0 points What is the conjugate acid of NO − 3 ? 1. HNO 3 correct 2. NO 2 − 3. NH 3 4. NO 3 2 − 5. H + 6. OH − Explanation: Since the question asks for the conjugate acid, we can assume NO − 3 is acting as a base. This means that it is a proton acceptor. To form the conjugate acid, it accepts a H making HNO 3 . 005 10.0 points According to the Bronsted-Lowry Theory of acids and bases, a base is 1. an electron donor. patino (mp25752) – H05: Acid/Base Equilibrium – McCord – (53215) 2 2. an electron acceptor. 3. a substance which when dissolved in water yields OH − . 4. a proton donor. 5. a proton acceptor. correct Explanation: Bases are defined by the Arrhenius the- ory as substances which in water produce hy- droxide ions, by the Bronsted-Lowry theory as substances which accept protons, and by the Lewis theory as substances which provide electron pairs. 006 10.0 points Which is NOT a conjugate acid-base pair? 1. H 2 O : OH − 2. HCl : Cl − 3. H 2 : H − 4. H 3 SO + 4 : H 2 SO 4 5. H 2 SO 4 : SO 2 − 4 correct Explanation: Except for H 2 SO 4 and SO 2 − 4 , the members of all of the pairs differ by one proton. 007 10.0 points The hydronium ion concentration in a solu- tion at pH 10 has what relationship to the hydronium ion concentration in a solution at pH 13?...
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This note was uploaded on 10/21/2009 for the course CH 53395 taught by Professor Lyon during the Spring '09 term at University of Texas.

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H05 Mccord - patino(mp25752 – H05 Acid/Base Equilibrium...

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