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# exam1dvb - Version 387 – Exam 1 – VANDEN BOUT –(53585...

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Unformatted text preview: Version 387 – Exam 1 – VANDEN BOUT – (53585) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points The pH of a solution of hydrochloric acid is 2.80. What is the molarity of the acid? 1. 4 . 2 × 10 − 3 M 2. 4 . 2 × 10 − 2 M 3. 6 . 3 × 10 − 2 M 4. 1 . 6 × 10 − 3 M correct 5. 6 . 3 × 10 − 3 M Explanation: pH = 2.80 [H + ] = 10 − pH = 10 − 2 . 80 = 1 . 6 × 10 − 3 M Since HCl is a strong acid, it is completely dissociated, so its concentration here is also 1.6 × 10 − 3 M. 002 10.0 points What is the H + ion concentration in a 0.50 mol/L solution of a weak base that has an ionization constant ( K b ) of 2.0 × 10 − 8 ? 1. 8 . × 10 − 16 mol/L 2. 1 . × 10 − 8 mol/L 3. 2 . × 10 − 10 mol/L 4. 1 . × 10 − 4 mol/L 5. 1 . × 10 − 10 mol/L correct Explanation: 003 10.0 points A typical fresh egg white will have a pH of 7.80. This corresponds to 1. [H 3 O + ] of 3 . × 10 − 8 M; [OH − ] of 3 . 3 × 10 − 7 M . 2. [H 3 O + ] of 7 . × 10 − 8 M; [OH − ] of 1 . 4 × 10 − 7 M . 3. [H 3 O + ] of 8 . × 10 − 7 M; [OH − ] of 1 . 3 × 10 − 8 M . 4. [H 3 O + ] of 8 . 5 × 10 − 7 M; [OH − ] of 5 . 5 × 10 − 7 M . 5. [H 3 O + ] of 1 . 6 × 10 − 8 M; [OH − ] of 6 . 3 × 10 − 7 M correct . Explanation: 004 10.0 points Consider a series of chloride salts (MCl 2 ). As the charge-to-size ratio of M 2+ (decreases, increases) the hydration energy of M 2+ (de- creases, increases, does not change) in magni- tude and the crystal lattice energy of MCl 2 (decreases, increases, may increase or de- crease) in magnitude. 1. increases; decreases; decreases 2. increases; increases; decreases 3. increases; increases; increases correct 4. decreases; decreases; increases 5. increases; decreases; increases 6. increases; does not change; may increase or decrease 7. decreases; increases; increases Explanation: As charge-to-size ratio increases, hydration energy and crystal latice energy also increase. 005 10.0 points Which of the following statements is true with respect to the autodissociation of water when sipping a glass of ice water? I. pH = pOH = 7 II. pH < 7 III. pH = pOH Version 387 – Exam 1 – VANDEN BOUT – (53585) 2 IV. pH > 7 1. I and III only 2. III and IV only correct 3. II only 4. IV only Explanation: Since water autodissociates, [H + ] = [OH − ]. For any given temperature, the pH of pure water is defined as neutral and pH = pOH. At 25 ◦ C neutral pH = 7. K a will be smaller than 1 × 10 − 7 at 0 ◦ C because water autodissociates less than 25 ◦ C. pH will therefore be greater than 7 at 0 ◦ C....
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## This note was uploaded on 04/12/2008 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas.

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exam1dvb - Version 387 – Exam 1 – VANDEN BOUT –(53585...

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