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Homework 6-solutions - phan(dtp377 Homework 6 sutclie(51045...

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phan (dtp377) – Homework 6 – sutcliffe – (51045) 1 This print-out should have 17 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. This HW covers through the end of Chapter 7 and will be on Exam 3. 001 10.0points A diprotic acid H 2 A has values of K a1 = 1 . 0 × 10 - 6 and K a2 = 1 . 0 × 10 - 10 . What is the [A 2 - ] in a 0.10 M solution of H 2 A? 1. 1 . 0 × 10 - 10 M correct 2. 0.10 M 3. 3 . 2 × 10 - 4 M 4. 3 . 2 × 10 - 6 M 5. 0.20 M Explanation: 002 10.0points What is the pH of a 0.020 M solution of hydrosulfuric acid, a diprotic acid? K a1 = 1 . 1 × 10 - 7 K a2 = 1 . 0 × 10 - 14 1. 9.67 2. 4.69 3. 7.84 4. 5.22 5. 7.00 6. 4.33 correct 7. 3.65 Explanation: Solve using ONLY the 1st ionization. So this works like any other monoprotic acid where the assumption [H + ] = radicalbig (Conc)( K a1 ) is valid. 003 10.0points Which equation represents K a2 for sulfurous acid? 1. HSO - 3 (aq) + H 2 O( ) H 2 SO 3 (aq) + OH - (aq) 2. SO 2 - 3 (aq) + H 2 O( ) HSO - 3 (aq) + OH - (aq) 3. H 2 SO 3 (aq) + H 2 O( ) HSO - 3 (aq) + H 3 O + (aq) 4. H 2 SO 3 (aq) + 2 H 2 O( ) SO 2 - 3 (aq) + 2 H 3 O + (aq) 5. HSO - 3 (aq) + H 2 O( ) SO 2 - 3 (aq) + H 3 O + (aq) correct Explanation: 004 10.0points Oxalic acid is a relatively strong diprotic acid with K 1 = 5 . 3 × 10 - 2 and K 2 = 5 . 3 × 10 - 5 . What is the [HC 2 O - 4 ] concentration in an ox- alic acid solution that is 0.10 M? 1. 0.10 2. 0.051 M correct 3. 0.027 M 4. 0.073 M 5. 5 . 3 × 10 - 5 Explanation: K 1 = 5.3 × 10 - 2 K 2 = 5.3 × 10 - 5 In this case, since we’re considering a solu- tion of H 2 C 2 O 4 and HC 2 O - 4 , we should use the expression for K 1 here: K 1 = [H + ] [HC 2 O 4 - ] [H 2 C 2 O 4 ]
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