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University of Texas CH 302 McCord H06 - Acid-Base 1

# University of Texas CH 302 McCord H06 - Acid-Base 1 -...

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byrne (cmb3744) – H06: Acid-Base 1 – mccord – (51620) 1 This print-out should have 21 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points What is the hydroxide concentration [OH ] in an aqueous solution in which the hydronium ion concentration [H 3 O + ] is 1 × 10 5 M? 1. 1 × 10 7 M 2. 1 × 10 14 M 3. 1 × 10 9 M correct 4. 1 × 10 5 M Explanation: [H 3 O + ] = 1 × 10 5 M K w = [H 3 O + ][OH ] = 1 . 0 × 10 14 [OH ] = K w [H 3 O + ] = 1 . 0 × 10 14 1 × 10 5 = 1 × 10 9 M 002 10.0points Which of the following is true in pure water at any temperature? 1. [H 3 O + ][OH ] = 1.0 × 10 14 2. pH = 7.0 3. [H 3 O + ] = [OH ] correct 4. K w decreases with increasing tempera- ture. 5. pH = 7.0 or greater than 7.0 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. 003 10.0points What is [H 3 O + ] when [OH ] = 3 . 3 × 10 9 M? 1. 1 . 0 × 10 7 M 2. 6 . 6 × 10 5 M 3. 3 . 3 × 10 9 M 4. 3 . 3 × 10 5 M 5. 3 . 0 × 10 6 M correct Explanation: [OH ] = 3 . 3 × 10 9 M K w = [H 3 O + ][OH ] = 1 × 10 14 [H 3 O + ] = K w [OH ] = 1 . 0 × 10 14 3 . 3 × 10 9 = 3 . 0 × 10 6 M 004 10.0points What is [OH ] when [H 3 O + ] = 8 . 2 × 10 5 M? 1. 6 . 3 × 10 9 M 2. 8 . 2 × 10 5 M 3. 1 . 0 × 10 7 M 4. 1 . 2 × 10 10 M correct 5. 1 . 2 × 10 4 M Explanation: [H 3 O + ] = 8 . 2 × 10 5 M K w = [OH ][H 3 O + ] = 1 . 0 × 10 14 [OH ] = K w [H 3 O + ] = 1 . 0 × 10 14 8 . 2 × 10 5 = 1 . 2 × 10 10 M 005 10.0points What is [OH ] in a 0.0050 M HCl solution? 1. 2 . 0 × 10 12 M correct

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byrne (cmb3744) – H06: Acid-Base 1 – mccord – (51620) 2 2. 1 . 0 × 10 7 M 3. 5 . 0 × 10 3 M 4. 1 . 0 M 5. 6 . 6 × 10 5 M Explanation: [OH ] = 0 . 0050 M Since HCl is a strong acid, it completely dissociates and H + is 0 . 0050 M. HCl H + + Cl K w = [H + ][OH ] = 1 × 10 14 [OH ] = K w [H + ] = 1 × 10 14 0 . 0050 = 2 × 10 12 M 006 10.0points What is the conjugate acid of NO 3 ? 1. NH 3 2. NO 2 3. H + 4. HNO 3 correct 5. OH 6. NO 3 2 Explanation: Since the question asks for the conjugate acid, we can assume NO 3 is acting as a base.
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