CHexam2 - Version 311 – Exam 2 – vanden bout –...

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Unformatted text preview: Version 311 – Exam 2 – vanden bout – (51640) 1 This print-out should have 32 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points What would be the pOH of a solution of Sr(OH) 2 (strontium hydroxide) prepared by dissolving 122 g of the base into 10 L of pure water (H 2 O)? 1. 0.7 correct 2. 1 3. 13.3 4. 13 Explanation: 122 g Sr(OH) 2 × 1 mol 122 g = 1 mol Sr(OH) 2 1 mol Sr(OH) 2 10 L H 2 O = 0 . 1 M Sr(OH) 2 Sr(OH) 2 (aq) ↔ Sr 2+ (aq) + 2 OH − (aq) [OH − ] = C b · 2 = 0 . 1M · 2 = 0 . 2M pOH =- log[OH − ] =- log(0 . 2) = 0 . 7 002 10.0 points Thallium(I) iodide and lead(II) iodide have nearly identical K sp values. If you had a saturated solution of each compound, which do you think would have the higher osmotic pressure? TlI K sp = 5 . 54 × 10 − 8 PbI 2 K sp = 9 . 8 × 10 − 9 1. TlI will be higher by more than a factor of 2 2. PbI 2 will be higher by more than a factor of 2 correct 3. they will be within a factor of 2 of each other Explanation: The highest osmotic pressure will be the solution with the highest concentration of ions. Even though they have similar K sp val- ues, the molar solubilities are quite different. The molar solubility of PbI 2 comes out to be 1 . 3 × 10 − 3 , while TlI is only 2 . 3 × 10 − 4 . Also, the PbI 2 has a van’t Hoff factor of 3 while that TlI is only 2. As a result the total con- centration of ions in the PbI 2 solution will be higher by a factor of more than 8. This means the osmotic pressure of the PbI 2 solution will be more than 8 times higher as the osmotic pressure is directly proportional to the total concentration of all solutes. 003 10.0 points Consider the titration of 50.0 mL of 0.0200 M HClO(aq) with 0.100 M NaOH(aq). What is the formula of the main species in the solution after the addition of 10.0 mL of base? 1. HClO 2 2. ClOH 3. ClO − correct 4. ClO 2 5. NaOH Explanation: 004 10.0 points Consider a glass of water at 80 ◦ C, which of the following statements is true? 1. The water is neutral because its pH is 7 2. The water is acidic because its pH is slightly lower than 7 3. The concentrations of H + and OH − are equal correct 4. The auto-protolysis of water is an exothermic process Explanation: Version 311 – Exam 2 – vanden bout – (51640) 2 The auto-protolysis of water is an endother- mic process since energy is needed to break the bonds. At a higher temperature, more H + ions exist due to higher energy, thus the pH of water decreases. The water is not acidic be- cause pH = pOH, although the K w is not 14 in this case. 005 10.0 points Assume that five weak acids, identified only by numbers (1, 2, 3, 4, and 5), have the following ionization constants....
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This note was uploaded on 05/02/2011 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas.

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CHexam2 - Version 311 – Exam 2 – vanden bout –...

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