Homework 5-solutions

# Homework 5-solutions - hernandez(ah29758 – Homework 5 –...

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Unformatted text preview: hernandez (ah29758) – Homework 5 – sutcliffe – (51045) 1 This print-out should have 14 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. Please note: ’p’ just equals ’negative log of’ 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, buffers and indicators will be on Exam 3. HW due the evening before the exam. 001 10.0 points How many grams of HNO 3 are needed to give a pH of 3 . 75 in an 11 . 5 L tank? The molar mass of HNO 3 is 63 . 1 g/mol. 1. 1.36 g 2. 0.0112 g 3. 0.00204 g 4. 0.0000324 g 5. 5.49 g 6. 2.19 g 7. 0.466 g 8. 0.000178 g 9. 0.129 g correct 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) × . 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 of 0 . 1 M HClO 2 (chlorous acid) aqueous solution was measured to be 1 . 2. What is the value of p K a for chlorous acid? 1. 2.57 2. 1.40 3. 0.11 4. 1.20 5. 3.91 6. 0.96 correct Explanation: M = 0 . 1 M pH = 1 . 2 Analyzing the reaction with molarities, HClO 2 + H 2 O ⇀ ↽ H 3 O + + ClO- 2 . 1-- x- x x . 1- x- x x [H 3 O + ] = [ClO- 2 ] = 10- pH = 10- 1 . 2 = 0 . 0630957 mol / L The...
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Homework 5-solutions - hernandez(ah29758 – Homework 5 –...

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