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CH302 Homework 6-solutions

# CH302 Homework 6-solutions - Bodet(ngb299 Homework 6...

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Bodet (ngb299) – Homework 6 – sutcli ff e – (51630) 1 This print-out should have 17 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The last three questions on this HW are to get you practicing on acid base stoichiometry reactions (i.e., titration calculations). Before you attempt Q8 and Q9 you may want to wait until I cover an additional discussion of polyprotic salts in class. 001 10.0 points A water solution of NaI will exhibit a pH value of 1. zero. 2. about 7. correct 3. less than 7. 4. greater than 7. Explanation: 002 10.0 points If the value of K b for pyridine is 1 . 8 × 10 - 9 , calculate the equilibrium constant for C 5 H 5 NH + (aq) + H 2 O( ) C 5 H 5 N(aq) + H 3 O + (aq) . 1. - 1 . 8 × 10 - 9 2. 1 . 8 × 10 - 9 3. 1 . 8 × 10 - 16 4. 5 . 6 × 10 8 5. 5 . 6 × 10 - 6 correct Explanation: 003 10.0 points I found some ammonium sulfate sitting in a can. I mixed it with some water I had sitting in a pan. It really mixed up nicely, I thought that I would say the solution was ? on this lovely day. 1. now acidic correct 2. still neutral 3. now just basic Explanation: Ammonium sulfate is the salt of a strong acid, so it is an acidic salt. 004 10.0 points Which solution has the highest pH? 1. 0.1 M of KNO 2 , K a HNO 2 = 4 . 5 × 10 - 4 2. 0.1 M of KHCOO, K a HCOOH = 1 . 8 × 10 - 4 3. 0.1 M of KCH 3 COO, K a HC 2 H 3 O 2 = 1 . 8 × 10 - 5 4. 0.1 M of KCl, K a HCl = very large 5. 0.1 M of KClO, K a HClO = 3 . 5 × 10 - 8 correct Explanation: 005 10.0 points What is [H 3 O + ] in a solution made by dissolving 0.200 mole of sodium acetate (NaCH 3 COO) in enough water to make one liter of solution? K a for CH 3 COOH is 1 . 80 × 10 - 5 . 1. 5.74 2. 9.02 3. 5 . 56 × 10 - 11 4. 9.25 5. 5 . 56 × 10 - 10 6. 10.25

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Bodet (ngb299) – Homework 6 – sutcli ff e – (51630) 2 7. 9 . 49 × 10 - 10 correct 8. 1 . 05 × 10 - 5 9. 4.98 10. 1 . 80 × 10 - 6 Explanation: 006 10.0 points What is the pH of a 0 . 37 M solution of anilin- ium nitrate (C 6 H 5 NH 3 NO 3 )? K b for aniline is 4 . 2 × 10 - 10 . Your answer must be within ± 0.4% Correct answer: 2 . 52752. Explanation: M C 6 H 5 NH 3 NO 3 = 0 . 37 M K b = 4 . 2 × 10 - 10 It’s a salt of a weak base (BHX). This means you need a K a for the weak acid BH + : K a = K w K b = 1 . 0 × 10 - 14 4 . 2 × 10 - 10 = 2 . 38095 × 10 - 5 You CAN use the approximation for the
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