HW 5 Solutions - Wright Jacqueline Homework 5 Due 11:00 pm...

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Wright, Jacqueline – Homework 5 – Due: Oct 10 2007, 11:00 pm – Inst: James Holcombe 1 This print-out should have 28 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points Acetic acid (CH 3 COOH) is generally classi- fied as 1. a weak base because it only partially ion- izes in solution. 2. a weak acid because it only partially ion- izes in solution. correct 3. a weak acid because it has three hydro- gens and a hydroxyl group. 4. a strong acid because it has four hydro- gens. 5. a weak base because it has one hydroxyl group. 6. a strong acid because if fully ionizes in solution. 7. amphoteric because it creates both pro- tons and hydroxyl ions in solution. Explanation: Acetic acid is only partially dissociated in water and so it is classified as a weak acid. 002 (part 1 of 1) 10 points The strength of an acid or base is a measure of 1. the strength of its attraction to water molecules. 2. how many hydroxide or hydrogen ions it contains. 3. how vigorously it reacts with the other molecules. 4. how completely it dissociates in aqueous solution. correct Explanation: Acids that completely dissociate in water are considered strong acids. If they do not completely dissociate, they are considered weak acids. The same works for bases. 003 (part 1 of 1) 10 points In the reversible reaction H 3 O + + NH 3 * ) H 2 O + NH + 4 , what two substances act as acids in the Bronsted-Lowry sense? 1. H 3 O + and NH + 4 correct 2. NH 3 and NH + 4 3. NH 3 and H 2 O 4. some other pair 5. H 3 O + and H 2 O Explanation: In this reaction, H 3 O + is donating a proton to OH - . Therefore H 3 O + is acting as an acid and OH - is acting as a base. In the reverse reaction, NH + 4 is the proton donor and thus, it is the other acid. 004 (part 1 of 1) 10 points The pH of a 1 × 10 - 8 M solution of HNO 3 is 1. 6.96 correct 2. 6 3. 8 4. 7 Explanation: [H + ] HNO 3 = 1 × 10 - 8 M HNO 3 is a strong acid and dissociates com- pletely, but since the acid is so dilute, water makes a great contribution of hydronium ions to the solution that needs to be taken into consideration. [H + ] H 2 O = 1 × 10 - 7 [H + ] total = 1 . 1 × 10 - 7
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Wright, Jacqueline – Homework 5 – Due: Oct 10 2007, 11:00 pm – Inst: James Holcombe 2 pH = - log ( 1 . 1 × 10 - 7 ) = 6 . 95861 005 (part 1 of 1) 10 points In the series HClO, HClO 2 , HClO 3 , HClO 4 , which is the strongest acid? 1. HClO 3 2. HClO 2 3. HClO 4 correct 4. HClO Explanation: For any series of compounds containing hy- drogen, oxygen and a non-metal, the acidity increases as the number of the oxygen atoms in the molecule increases. 006 (part 1 of 1) 10 points The pH of a human blood sample was mea- sured to be 7.41. What is the [OH - ] in this blood? 1. 4 . 12 × 10 - 7 mol/L 2. 6 . 05 × 10 - 7 mol/L 3. Cannot be determined from the informa- tion given. 4. 3 . 89 × 10 - 8 mol/L 5. 2 . 57 × 10 - 7 mol/L correct 6. 6.59 mol/L Explanation: pH = 7.41 pOH = 14 - pH = 14 - 7 . 4 = 6 . 59 [OH - ] = 10 - pOH = 2 . 57 × 10 - 7 007 (part 1 of 1) 10 points Assume that five weak acids, identified only by numbers (1, 2, 3, 4 and 5), have the follow- ing ionization constants.
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