Answer Key_Exam 4 - Version 244 Exam 4 rowland (53210) 1...

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: Version 244 Exam 4 rowland (53210) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points An aqueous solution has a dilute HCl concen- tration of 0.0000000001 M at 298 K. What is the approximate pH and why? 1. 7, because the water contributes the ma- jority of the H + . correct 2. 9, because HCl is a weak acid and does not dissociate completely. 3. 4, because pH + pOH = 14. 4. 10, because HCl is a strong acid. 5. 10, due to the reaction of water with the acid. Explanation: pH is due to the H + concentration. In this solution, the 0.0000001 M H + comes from water and a much smaller contribution comes from the very dilute acid. It does not make sense that adding acid to water would make the solution go very basic, so pH of 9 or 10 is illogical and incorrect. 002 10.0 points For the titration of 50.0 mL of 0.020 M aque- ous salicylic acid with 0.020 M KOH(aq), cal- culate the pH after the addition of 55.0 mL of KOH(aq). For salycylic acid, p K a = 2.97. 1. 7.00 2. 10.98 correct 3. 12.30 4. 11.26 5. 12.02 Explanation: 003 10.0 points For the reaction 2 A + B products and the data Initial Initial Conc., M Rate, M/s A B 0.10 0.10 2 . 10- 2 0.20 0.10 8 . 10- 2 0.30 0.10 1 . 8 10- 1 0.20 0.20 8 . 10- 2 0.30 0.30 1 . 8 10- 1 find the rate law. 1. rate = k [A] 2 correct 2. rate = k [A] [B] 3. rate = k [A] [B] 4. rate = k [A] 5. rate = k [B] 2 Explanation: 004 10.0 points Based on the plot below, what are the units of the rate constant for this reaction? [A] (M) time (min) Version 244 Exam 4 rowland (53210) 2 1. s- 1 2. M- 1 min- 1 3. M min- 1 correct 4. M- 1 s- 1 Explanation: The y-axis is presented in units of concen- tration. This, together with the fact that the line has a constant slope, tells us that this is a zero order process. The x-axis tells us the time unit is minutes. 005 10.0 points The figure below shows the titration of a monoprotic weak acid with a strong base. b b I II Volume of base added pH The pH at point I is equal to the and the pH at point II is 7. 1. pH of the acid; greater than 2. p K a of the acid; less than 3. pH of the acid; less than 4. p K a of the acid; equal to 5. p K a of the acid; greater than correct Explanation: 006 10.0 points If the average rate of decomposition of PH 3 (g) is 3 . 2 (mol PH 3 ) / L / min for the reaction 2 PH 3 (g) 2 P(g) + 3 H 2 (g) , what is the unique average reaction rate? 1. 1 . 6 mol / L / min correct 2. 3 . 2 mol / L / min 3. 4 . 8 mol / L / min 4. 6 . 4 mol / L / min 5. 2 . 1 mol / L / min Explanation: 007 10.0 points A buffer solution contains 0.25 M NaNO 2 (aq) and 0.80 M HNO 2 (aq) (p K a = 3.37). What is the pH after 0.10 mol HBr is added to 1.00 L of this buffer?...
View Full Document

This note was uploaded on 01/30/2010 for the course GOV 312L taught by Professor Madrid during the Fall '07 term at University of Texas at Austin.

Page1 / 8

Answer Key_Exam 4 - Version 244 Exam 4 rowland (53210) 1...

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