Homework 5-solutions

# Homework 5-solutions - phan(dtp377 Homework 5 sutclie(51045...

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phan (dtp377) – Homework 5 – sutclife – (51045) 1 This print-out should have 14 questions. Multiple-choice questions may continue on the next column or page – Fnd all choices be±ore answering. Please note: ’p’ just equals ’negative log o±’ so we can have pH, pOH , pK a etc. This HW combined with HW 3 4 will cover us up to exam 2, so polyprotic acids, protonation state, salts, neutralizations, bufers and indicators will be on Exam 3. HW due the evening be±ore the exam. 001 10.0 points How many grams o± HNO 3 are needed to give a pH o± 3 . 75 in an 11 . 5 L tank? The molar mass o± HNO 3 is 63 . 1 g/mol. 1. 0.00204 g 2. 0.466 g 3. 2.19 g 4. 1.36 g 5. 0.0000324 g 6. 0.000178 g 7. 0.129 g correct 8. 5.49 g 9. 0.0112 g Explanation: pH = 3 . 75 V = 11 . 5 L MM = 63 . 1 g/mol [H + ] = 10 - pH = 10 - 3 . 75 = 0 . 000177828 Since HNO 3 is a strong acid, HNO 3 (aq) H + (aq) + NO - 3 (aq) . One HNO 3 one H + , so [H + ] = [HNO 3 ] = 0 . 000177828 M and (11 . 5 L) × 0 . 000177828 mol HNO 3 1 L = 0 . 00204502 mol HNO 3 . Thus (0 . 00204502 mol HNO 3 ) × 63 . 1 g HNO 3 1 mol HNO 3 = 0 . 129041 g HNO 3 002 10.0 points The pH o± 0 . 1 M HClO 2 (chlorous acid) aqueous solution was measured to be 1 . 2. What is the value o± p K a ±or chlorous acid? 1. 3.91 2. 2.57 3. 1.20 4. 0.96 correct 5. 0.11 6. 1.40 Explanation: M = 0 . 1 M pH = 1 . 2 Analyzing the reaction with molarities, HClO 2 + H 2 O H 3 O + + ClO - 2 0 . 1 - 0 0 - x - x x 0 . 1 - x - x x [H 3 O + ] = [ClO - 2 ] = 10 - pH = 10 - 1 . 2 = 0 . 0630957 mol / L The K a is K a = [H 3 O + ][ClO - 2 ] [HClO 2 ] = (0 . 0630957) 2 0 . 1 - 0 . 0630957 = 0 . 107876 and the p K a is p K a = - log(0 . 107876) = 0 . 967077 .

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Homework 5-solutions - phan(dtp377 Homework 5 sutclie(51045...

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