Practice Exam 4 Key Essay

Submitted By gsteven
Words: 1931
Pages: 8
Open Document
A

Chemistry 1252

Exam #4 KEY (90 minutes) August 6, 2012

First Name Last Name

Signature

Page

Points

2

20

3

26

4

27

5

27

Total

100

SID# 800‐

Score

Grader

You must sign to affirm that you have followed the UNC Charlotte Student Code of Academic Integrity, or your exam will not be graded.

You may assume the 5% rule on all problems without checking the rule. Please read each question carefully and answer it completely and clearly. Most of the factual information you need is contained in the text of the problem. Answer the questions you find easy first; questions which appear difficult at first usually require a revision of your thought process. Always keep in mind the intended examination topics if a problem appears too hard. The quiz should have 5 pages for a total of 10 questions. Individual point values for free response are given in the corner of each answer space. You must show your work to receive any credit for problems involving calculations. All calculated answers and work must include units, and should be rounded to the appropriate number of significant figures!

88.91

1

A
Free Response Instructions: Solve the following problems in the boxes provided below each question.
Be sure to show all your work and units, and round your answers to the appropriate significant figures at the end of each part. FOR ALL PARTS: 1 for MISSING UNITS 1. A 100.0 mL sample of 0.100 M methylamine (CH3NH2, Kb = 3.710‐4) is titrated with 0.250 M HNO3. (a) Calculate the pH after the addition of 15.0 mL of acid. CH3NH2(aq) + H3O+(aq)  CH3NH3+(aq) + H2O(l) +1 correct reaction 0.0100 mol 0.00375 mol 0 mol |
+1 correct BCA B
C
‐0.00375 mol ‐0.00375 mol + 0.00375 mol |

+1 Kb  Ka ‐14
‐4
0.00625 mol 0 mol 0.00375 mol Ka = 1.010 /3.710 = 2.710‐11 A
+1 H‐H equation setup with base/acid (consistent)
+1 answer ‐14 / 3.710‐4) + log (0.00625 mol / 0.00375 mol) = 10.79 pH = log(1.010 5 (b) What is the pH at the equivalence point? 0.1000 L(0.100 M CH3NH2) = 0.0100 mol CH3NH2  0.0100 mol H3O+ = 0.250 M HNO3(V)  V = 0.0400 L For incorrect reactions, +3 maximum.
CH3NH2(aq) + H3O+(aq)  CH3NH3+(aq) + H2O(l) 0.0100 mol 0.0100 mol 0 mol | +1 correct reaction + After B
C
‐0.0100 mol ‐0.0100 mol + 0.0100 mol | +1 Vtot, +1 mol  M (consistent) +
NH
A
0 mol 0 mol 0.0100 mol |
[CH
3
3 ] = 0.0100 mol / 0.140 L

= 0.071429 M CH3NH3+ +1 correct reaction/ICE table +
+
+1 Ka setup with correct Ka CH
3NH3 (aq) + H2O(l) CH3NH2(aq) + H3O (aq) ‐11 = x2 / 0.071429 M ‐ x 0 M 0 M 2.70310
I
0.071429 M | ‐x | + x
+x

x = 1.38910‐6 +1 answer C x x pH = ‐log(x) = 5.86
0.071429 M – x | E
6

(c) What major post‐equivalence point species are present? (List species present AFTER the strong reaction but BEFORE equilibrium is established.)
H2O
H3O+
CH3NH3+

+1/2 each
NO3
2

(d) In part (c), what effect allows you to ignore the weak acid in solution when calculating the pH? Explain. If “weak versus strong,” +1 description. Common‐ion effect: +1 Although CH3NH3+ is present, H3O+ is a common‐ion (product) in the reaction +2 common‐ion explained CH3NH3+(aq) + H2O(l) CH3NH2(aq) + H3O+(aq), so this reaction will be suppressed.
3

2. (a) Describe how to make 1.00 L of 1:1 HCO3/CO32 buffer solution from solid Na2CO3 and 1.00 M HCl.
(Assume that the solid does not displace the volume of the solution.) Be specific with numerical amounts! +4 ratio of 2 (weak base): 1(strong
Show More

Related Documents: Practice Exam 4 Key Essay

Question and Correct Answer Essay

Exam 1 Review Notes Overview-- 50 questions, Multiple Choice. Similar format to practice exam. Need to bring a #2 pencil. Scantrons will be provided. The goal is to have no trick questions. Answers will be straightforward and will not be convoluted. Normally, you can eliminate 3 of the 5 answers … if you are still confused go back to the question for a possible indication of what the correct answer is. Usually there will be a key word or phrase that will clue you in to the correct answer…

Words 492 - Pages 2

Syllabus: Finance and Class Essay

Doh-Khul Kim, Ph.D. (Chair & Associate Professor of Economics and Finance) Office and Phone 125 S. Loomis House (Room 103) (630) 637-5243 dkim@noctrl.edu (email) Office Hours Mon/Wed. 2:00 – 3:00 pm Tue/Thu. 4:00 – 5:00 pm Fri. No Office Hours (Appointment Only) Textbooks Fundamentals of Financial Management by Brigham and Houston (Concise 7th edition), Thomson (2012): required Additional Materials Wall Street…

Words 1571 - Pages 7

SylSpring2015 Online Essay

Office: 316 Prentis Hall Telephone: (313) 577-4581 (Office) (313) 577-4515 (Dept. of Management) Fax: (313) 577-5486 E-Mail: a.levi@wayne.edu or alevi@sbcglobal.net Office hours: Thursdays 2:00 - 4:00 PM or by appointment Course Prerequisite BA 7040 (Managing Organizational Behavior) Course description The importance of human resource management (HRM)—the use of a firm’s human resources to achieve organizational objectives—has increased steadily…

Words 1943 - Pages 8

Independent Study Guide

relevant sections from the text book, including key definitions and examiners' tips. Answer questions from the text book at the end of each double page. Have a go at practice questions and examination questions at the end of each chapter. Check through the specification (found at www.ocr.org.uk) to make sure you understand the concepts you have covered in class. Learn your definitions for key words. Practice calculations for magnification. Work through past exam papers and look at mark schemes to see what…

Words 5145 - Pages 21

Essay on Exam Sample

Decision Making (SOU) Semester 5, 2012 Examination Information for ORDINARY, DEFERRED AND SUPPLEMENTARY EXAMINATIONS Time Allowed: THREE (3) hours + 15 minutes reading time (you are permitted to write during reading time) Instructions: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. There are SIX (6) questions to be marked out of a total 100 marks. Some questions have more than one part. Answer ALL questions. You may answer the questions in any order but PLEASE clearly identify…

Words 837 - Pages 4

Roles Of A Defense Attorney Essay

it should. They responsible for defending individuals who are charged with crimes and felonies. A prosecutors and defense lawyers complete the same education. Prosecutors and defense attorneys are both key players in the criminal court system. Judges and prosecutors hold a dangerous role as key actors in the prevention of anguish. Judges determine the guilt or innocence of criminal defendants and impose sentences on defendants found guilty. Prosecutors are charged with the responsibility of enforcing…

Words 817 - Pages 4

Essay about bus475 logics

Syllabus School of Business BUS/475 Version 4 Integrated Business Topics Copyright © 2009, 2007 by University of Phoenix. All rights reserved. Course Description The integrated business topics course examines strategic business management while integrating topics from previously completed business foundation coursework. This allows students to demonstrate a comprehensive understanding of the undergraduate business curricula with a significant emphasis placed on the assessment of individual…

Words 3052 - Pages 13

LLP English Leading The Learning ERW Andy Goudge Essay

Rationale and context for the project (750 words) In my current role as head of Physics the performance of pupils in terminal exams at Key Stage 5 is of significant concern. My year 12 pupils progressed well throughout the course between September 2012 and June 2013. This was demonstrated throughout various assessments during the year. When they reached their terminal exams however the entire cohort performed significantly lower than the ability demonstrated to me through my own assessment. This year…

Words 7008 - Pages 29

Cognitive Memory Strategies

words to study, not only the spelling of but they also encouraged us to practice our vocabulary by practicing using them in sentences. At the beginning of every week, after my teachers had given me and my classmates our list of words to study, when I went home from school, I used to sit in my room and rehearse those words; I would typically read them off the list, and then I would look away from the list and then I would practice spelling them until I felt confident and satisfied that I knew how to…

Words 1453 - Pages 6

Essay on Standardized Test and Study Guide

also make note of the types of questions that will be on the exam- multiple choice and true/ false. Day 2: Write down key points talked about in class. Review your notes and read chapter 2 to prepare for the next class. 2 Day 3: After class review your notes and then visit your teacher in their office hours to clear up anything that you got caught up with during the week, then create some space for yourself tonight to read chapter 3 Day 4: Ask questions in class about any information about last week…

Words 1124 - Pages 5