Practice Exam 1 Sp 2014_Final

8/13/2019 Practice Exam 1 Sp 2014_Final

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PLEASE NOTE:

This practice exam for Sp14 is the same as the original exam given by Professor Bleeke in Spring 2013. Thepractice exam consists of questions covering representative topics, but not necessarily all of the subject matter

discussed so far this semester.


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Please print LASTname: ________________________ Please print FIRSTname: ____________________

Signature: ____________________________________ Student ID #: _________________________________

Chemistry 112A PRACTICE FIRST EXAM.

PLEASE WRITE YOUR NAME ON EACH PAGE OF THE EXAM.

TURN IN THE ENTIRE EXAM (INCLUDING THE SCRATCH PAGE) WHEN YOU ARE FINISHED!

1.5 HOURSwill be allowed for the exam. The examinationcontains 9 questions on 14 numbered pages. Some of the

questions contain more than one part. You must clearly andneatlyshow your work and your reasoning used to arrive at

the correct answer, in the space provided, in order to receivefull credit. Partial credit will be given for partially correct

reasoning in support of incorrect or correct final answers.Free written responses (i.e. justifications) need to be well-written (in complete sentences), fully introduce an idea or

concept, develop that idea or concept, and clearly lead to a

well-defined conclusion.

No credit will be given unless the answers are legibly writtenin the spaces provided. If you run out of space, use the

scratch page at the end of the exam, please write your nameon that page, and clearly label the answers you place there.Do not write on the backs of the exam pages; they will not

be graded. No books, notes, other students exams, electronicdevices (with the exception of the course-approved

calculators) or any other resource materials are allowed.

REGRADE INFORMATION:Read the syllabus section on

regrades on the general information sheet. Regrade requestsmust be placed in the wood cabinet labeled Regrades, by

the racks on the 2nd floor of the Lab Sciences Building.Attach the regrade form to the front of the exam stating

which questions you would like regraded and the gradingerrors that have been made.

DO NOT MAKE ANY MARKS OR CHANGES ON

THE EXAM ITSELF. DO NOT WRITE ANYTHING

ON THE EXAM! Regrade requests must be turned in by

4:30 PMon the due date.

Chemistry 112A Academic I ntegr ity Poli cy:

Students are expected to strictly adhere to Washington Universitys academic integrity policy. Any violation of this

policy, including but not limited to cheating on examinations or regrade requests, will be referred to WashingtonUniversitys Committee on Academic Integrity, and we will follow the committees recommendations.

In accordance with the academic integrity policy of Washington University and the common practice of respect forothers in our community, I submit this work, which is solely my own, for evaluation. I now state that I have not had

prior access to this examination and in the course of this examination will not contact anyone, or use any otherresources that have not been specifically noted as acceptable by the faculty member, and/or a designee,

administering the examination.

Signature:_____________________________________________ Date:________________

For grading only:

1.__________ (09 pts)

2._________ (05 pts)

3.__________ (14 pts)

4.__________ (10 pts)

5. __________ (12 pts)

6.__________ (12pts)

7.__________ (14pts)

8.__________ (12 pts)

9.__________ (12 pts)

Total Points: _______________

(100 pts)


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Please print LASTname: ________________________ Please print FIRSTname:___________________

1. (09 Total Points) Given the following titration curve, answer the questions below.

Circle the answer(s) that make the following statements TRUE.

a) The titration curve shown is one for aA) strong acid being titrated by a strong base.B) strong base being titrated by a strong acid.C) weak acid being titrated by a strong base.D) weak base being titrated by a strong acid.

b) (Please refer to Table 11.3 on your Formulas, Constants, Conversion Factors, etc. reference sheet for thisquestion). The best choice of an indicator for this titration (of the following choices) is

A)bromophenol blueB) litmusC)phenol redD)phenolphthaleinE) not shown here (i.e. none of the above would be a good choice of indicator).

c) For the acid used in the titration shown above, the KBvalue of its conjugate base is.A) larger than the KAvalue of the acid.B) smaller than the KAvalue of the acid.C) equal to the KAvalue of the acid.D)Not a value that one can determine from a titration curve.

d) The equivalence point is reached whenA) 30 mL of the titrant has been added.B) 60 mL of the titrant has been added.C) 100 mL of the titrant has been added.D) The equivalence point is not reached during this titration.

2.00

4.00

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0 10 20 30 40 50 60 70 80 90 100

pH

Volume of Titrant Added (mL)

Continues to Next Page


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1. (Continued) Copied from previous page: Given the following titration curve, answer the questions below.

Circle the answer(s) that make the following statements TRUE.

e) (For this question, HA refers to a weak acid). When 80 mL of the titrant have been added(Notethere may be more than 1 correct answer.)

A) HA is a major species in solution.B) OHis a major species in solution.C) H3O+is a major species in solution.D) There is no HA present in solution.E) HA is present, but is a minor species in solutionF) Ais a major species in solutionG) Ais a minor species in solution

f) The value of KAfor the acid used in the titration shown aboveA) is 1.0 104.B) is 1.0 108.C) Is 1.0 1010.D) is 1.8 104.E) cannot be determined without knowing the concentration of the titrant.

g) The area of the titration curve shown above that can best be described as a buffer solutionA) occurs between 0-20 mL of titrant added.B) occurs between 20-40 mL of titrant added.C) occurs between 50-70 mL of titrant added.D) occurs between 70-90 mL of titrant added.E)None of the above. A buffer solution is not obtained during a titration.

09

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0 10 20 30 40 50 60 70 80 90 100

pH

Volume of Titrant Added (mL)


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2.(05 Total Points)a) Explain in 1-2 sentences why trichloroacetic acid (Cl3CCO2H) is a stronger acid than

acetic acid (H3CCO2H) on the lines provided. (The Pauling electronegativity values are provided in the table

below).

Pauling electronegativities:

H 2.20 Al 1.61 Se 2.55

Li 0.98 Si 1.90 Br 2.96

Be 1.57 P 2.19 Rb 0.82

B 2.04 S 2.58 Sr 0.95

C 2.55 Cl 3.16 In 1.78

N 3.04 K 0.82 Sn 1.88

O 3.44 Ca 1.00 Sb 2.05

F 3.98 Ga 1.81 Te 2.10

Na 0.93 Ge 2.01 I 2.66

Mg 1.31 As 2.18

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b) Where would you place trifluoroacetic acid (F3CCO2H) on this scale (circle one):

A) More acidic than trichloroacetic acidB) Between trichloroacetic acid and acetic acidC) Less acidic than acetic acid

03

02

05


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3. (14 Total Points) Consider the balanced reaction O2 (g) + 4HCl (g) 2Cl2 (g) + 2H2O (g), which has a

Kcof 1.10 x 106

at 1300 K. H for this reaction is114.4 kJ/mol.

a) Is the equilibrium conversion of O2 and HCl to Cl2 and H2O favored at higher or lower

temperature? Briefly explain your answer in 1-2 complete sentences on the lines provided.

______________________________________________________________________________

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b) Is the equilibrium conversion of O2 and HCl to Cl2 and H2O favored at higher or lower

pressure? Briefly explain your answer in 1-2 complete sentences on the lines provided.

______________________________________________________________________________

______________________________________________________________________________

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c) If 0.79 moles each of Cl2and H2O are introduced into a sealed 5.0 L vessel at 1300 K, how

many moles of HCl are present at equilibrium? Show all work to support your answer and circle

your final answer.

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10

02

02


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4.(10 Total Points)a) 0.78 grams of the weak acid HNO2 (Ka= 4.6 104

) are dissolved in 600 mL of an

already acidic, aqueous solution. If the pH of the final solution is 2.17, what was the initial pH of the acidic,

aqueous solution? Show all work to support your answer and circle your final answer.

10


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5. (12 Total Points) Suppose that you want to prepare an acetic acid solution that has the same percent

dissociation as 0.100 M propionic acid. What must the molarity of that acetic acid solution be? (Note: the

molarities in this problem refer to the initial concentrations of acid, not the equilibrium concentrations.) Please

show all work and circle your final answer.

Please use HOAc and HOPr as abbreviations for acetic acid and propionic acid, respectively, in your ICE tables

Acetic acid (HOAc) Ka= 1.8 x 105

Propionic acid (HOPr) Ka= 1.3 x 105

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6.(12 Total Points)a) Consider the balanced reaction 3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2 (g). At 1200 K, the

gaseous equilibrium mixture consists of 86% H2O by mass. Calculate Kc for the reaction. Show all work to

support your answer and circle your final answer.

b) Using your answer from part a, calculate Kp for the following reaction. Show all work to

support your answer and circle your final answer.

Fe3O4(s) + H2 (g)

Fe(s) + H2O(g)

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7. (14 Total Points) Consider the balanced chemical reaction: . Two separate

equilibria are established at the same given temperature. For the first equilibrium, 0.500 M CO and 0.100 M Cl2

are initially sealed in a vessel. For the second equilibrium, 0.119 M COCl2is initially sealed in a vessel. After

each system reaches equilibrium, each vessel contains the same concentration of COCl2. What is the value of

KC for this reaction at this given temperature? Show all work to support your answer and circle your final

answer. Hint: Use a different variable in the change line of each of your ICE tables.

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8.(12 Total Points)The antimalarial drug quinine, C20H24O2N2, is a diprotic weak base.

a) Write equations for the weak base equilibria corresponding to pKb1= 6.0 and pKb2= 9.8Use B, HB

+, and H2B

2+to represent the quinine and its protonated forms.

b) 1.0 gram of quinine is dissolved in 1900 mL of water. What is the pH of this solution? Showall work to support your answer and circle your final answer.

c) What is the concentration of H2B2+in this solution? Show all work to support your answerand circle your final answer.

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9.(12 Total Points)Consider the balanced exothermic reaction I2 (g) + Cl2 (g)2ICl (g)at equilibrium. Below

each of the following graphs, write the letter(s) corresponding to the stress(es) that could account for the shift

illustrated. In each case, the stress occurs at t1. If a graph does not correspond to any of the stresses listed

write none.Note: there may be more than 1 correct answer for each graph.

A) Removing Cl2B) Increasing the temperatureC) Adding an inert gas at constant volumeD) Adding I2E) Decreasing the volumeF) Adding a catalyst

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Time

Concent

ration

t1

I2

ICl

Time

Concent

ration

t1

I2

ICl

Time

Concent

ration

t1

Cl2

ICl

Time

Concentration

t1

I2

ICl

Time

Concentration

t1

I2

Cl2

Time

Concentration

t1

I2

ICl

End of Exam


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BLANK SCRATCH PAGE


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Formulas, Constants, Conversion Factors, etc.

Ideal Gas Law: PV = nRT

Solution to the quadratic equation ax2+ bx + c = 0:

2 1/2b (b 4ac)x

2 a

Kw= KaKb= 1.0 10

14at 25C

;

Henderson-Hasselbalch Equation: pH = pKalog10o

o

[HA]

[A ]

Physical Constants:

Avogadros number N0= 6.022137 1023

Universal gas constant R= 0.08206 L atm mol

K


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Practice Exam 1 Sp 2014_Final

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