solution7_pdf - ig996 Homework 7 Lyon (53565) 1 This...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ig996 Homework 7 Lyon (53565) 1 This print-out should have 24 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. This homework is due Thursday, March 6 by 12:00pm. 001 10.0 points A lake in central Texas contains 1 billion liters of water. The pH is normally 6.0, but it is tested at 5.0 and the fish are in danger. How much CaCO 3 should be dumped in to bring the pH back to 6.0? Assume CaCO 3 + H + Ca 2+ + HCO 3 The molecular weight of CaCO 3 is 100.1 g/mol. 1. 900 kg correct 2. 157 kg 3. 90 kg 4. 900,000 kg 5. 157 g Explanation: V = 10 9 L pH normal = 6 . pH current = 5.0 CaCO 3 = 100.1 g/mol [H 3 O + ] needed = [H 3 O + ] current- [H 3 O + ] normal = (10 5 .- 10 6 . ) M = 9 . 10 6 M CaCO 3 + H 3 O + Ca 2+ + HCO 3 + H 2 O n CaCO 3 = n H 3 O + = (10 9 L)(9 . 10 6 mol / L) = 9 . 10 3 mol m CaCO 3 = (9 . 10 3 mol)(100 . 1 g / mol) = 9 . 10 5 g = 900 kg 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. 0.11 3. 0.96 correct 4. 1.20 5. 3.91 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 . 1-- x- x x . 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 . 1- . 0630957 = 0 . 107876 and the p K a is p K a =- log(0 . 107876) = 0 . 967077 . 003 10.0 points A solution is prepared by dissolving NaCl in water. The pH of this solution is closest to ig996 Homework 7 Lyon (53565) 2 1. 11. 2. 7. correct 3. 5. 4. 9. 5. 3. Explanation: NaCl is a neutral salt. It does not alter pH. 004 10.0 points A 0.28 M solution of a weak acid is 3.5% ionized. What is the pH of the solution? 1. 0.55 2. 3.17 3. 2.01 correct 4. 5.25 5. 1.46 Explanation: M = 0 . 28 M P = 3 . 5% 3 . 5% of the 0 . 28 M is ionized (contributes to pH), so [H + ] = (0 . 28 M) 3 . 5 100 = 0 . 0098 M pH =- log[H + ] =- log(0 . 0098) = 2 . 00877 005 10.0 points What is the H 3 O + concentration of a 0.15 M solution of NH 4 Cl in H 2 O at 25 C? ( K b for NH 3 = 1 . 8 10 5 ) 1. 9 . 1 10 6 M correct 2. 1 . 6 10 3 M 3. 1 . 1 10 9 M 4. 1 . 10 14 M 5. 4 . 9 10 5 M 6. 8 . 2 10 1 M Explanation: C a = 0 . 15 K w = 10 14 K b = 1 . 8 10 5 NH + 4 NH 3 + H + K a = K w K b = 10 14 1 . 8 10 5 = 5 . 56 10 10 Since NH + 4 is a weak acid, use the weak acid equation: [H + ] = radicalbig K a C a = radicalBig...
View Full Document

Page1 / 7

solution7_pdf - ig996 Homework 7 Lyon (53565) 1 This...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online