Quiz 5-solutions - bu±er solution 1 The cation from the...

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Version 032 – Quiz 5 – fakhreddine – (51615) 1 This print-out should have 5 questions. Multiple-choice questions may continue on the next column or page – Fnd all choices before answering. 001 2.0 points Consider mixing HNO 3 and NaNO 3 . This is NOT a bu±er because 1. NO - 3 reacts with water to form NO 2 (g). 2. Na reacts with water to form OH - . 3. HNO 3 is not a weak acid. correct 4. NaNO 3 is not soluble. 5. NaNO 3 is basic. Explanation: 002 2.0 points When sodium formate is added to HCOOH(aq), 1. the pH of the solution increases. correct 2. the pH of the solution does not change. 3. the pH of the solution decreases. 4. the equilibrium concentration of HCOOH(aq) decreases. 5. the K a increases. Explanation: 003 2.0 points What is the pH of an aqueous solution that is 0.60 M (CH 3 ) 3 N ( K b = 6 . 5 × 10 - 5 ) and 0.95 M (CH 3 ) 3 NHCl? 1. 3.99 2. 9.81 3. 10.01 4. 9.61 correct 5. 4.39 Explanation: 004 2.0 points Explain why the salt of a weak acid, as well as the acid itself, must be present to form a
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Unformatted text preview: bu±er solution. 1. The cation from the salt is needed to partially neutralize added acid. 2. The anion from the salt is needed to partially neutralize added base. 3. Actually, a weak acid by itself is a bu±er; no salt is needed. 4. The cation from the salt is needed to partially neutralize added base. 5. The anion from the salt is needed to partially neutralize added acid. correct Explanation: The salt of the acid provides the anion which is the conjugate base of the bu±er sys-tem: HA + H 2 O ⇀ ↽ A-+ H 3 O + This anion A-reacts with any added acid (H 3 O + ) to prevent any appreciable change in pH. 005 2.0 points What is the pH of an aqueous solution that is 1.0 M HClO ( K a = 3 . × 10-8 ) and 0.75 M NaClO? 1. 6.36 2. 7.64 3. 7.40 correct 4. 7.52 5. 6.60 Explanation:...
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