CHEMISTRY 221 - Dr. Powers
Final Exam - FALL 2006
PRINT NAME ______________________________________________
(Last)
(First)
(MI)
ID# ___________________________
Signature ________________________________________
THIRD EXAM
Lab Section______
December 11, 2006
BE SURE YOU HAVE
16
DIFFERENT PAGES OF THIS EXAM
**********WRITE YOUR NAME ON EVERY PAGE****************
SHOW ALL WORK - NO WORK - NO CREDIT
REPORT ALL ANSWERS WITH CORRECT LABELS AND SIGNIFICANT FIGURES
•
•
•
•
•
•
All Cell phones must be turned off and cannot be used as a calculator.
You may use a calculator, and an exam data sheet.
Raise your hand if you have a question.
Keep your eyes on your own paper.
Several exam forms may be in use. It is a code violation if data from another exam form appears
on your paper.
Keep all REQUIRED exams as part of your records.
REQUEST FOR REGRADE
_______________Date
EXAMS SUBMITTED FOR REGRADES SHOULD NOT LEAVE THE RESOURCE CENTER!
Please regrade question
because___________________________________________
_________________________________________________________________________
_________________________________________________________________________
Please regrade question
because __________________________________________
_________________________________________________________________________
_________________________________________________________________________
Please regrade question
because __________________________________________
_________________________________________________________________________
______ Check here if there is a mistake in addition.
You must sign your regrade request, or it will not be considered a valid request.
I accept responsibility for all answers contained herein. ________________________________
Signature
When submitting regrade request, do not write on exam pages. Additional questions or comments are to
be placed on a separate sheet of paper and turned in with your test. Sign these as well.
Chemistry 221 – Final Exam Fall 2006
Question No.
Section I (new)
page 2
Name
Possible Points Points Earned TA Initials
1
24
2
3
4
5
Subtotal
25
20
11
20
100
Section II (review)
6
5
7
5
8
10
9
5
10
5
11
10
12
5
13
5
14
5
15
10
16
5
17
10
18
10
19
10
Subtotal
100
Total
200
Chemistry 221 – Final Exam Fall 2006
page 3
Name
Some Useful Information:
Gaussian Curve:
Student’s t
Q test:
Values of Q for rejection of data
Q (90%
0.94 0.76 0.64 0.56 0.51 0.47 0.44
confidence)
Number of
3
4
5
6
7
8
9
Observations
0.41
10
Chemistry 221 – Final Exam Fall 2006
page 4
Name
Chemistry 221 – Final Exam Fall 2006
page 5
Name
Chemistry 221 – Final Exam Fall 2006
page 6
Name
USEFUL EQUATIONS
Dilution of a solution
Percent Composition
M1V1 = M2V2
Weight percent 
mass of subs tan ce
x ( 100 )
mass of total solution or total sample
Correction for Buoyancy
Volume percent 
volume of subs tan ce
x ( 100 )
volume of total solution or total sample
d
m' ( 1  a )
dw
m
d
(1  a )
d
d a  0.46468 (
weight  volume percent 
mass of subs tan ce
x ( 100 )
volume of total solution or total sample
B  0.3783V
)
T
Gaussian Curve:
n
( x   )
y
1
 2
e
n
 xi
2
  xi  x 2
x  i 1
n
2 2
s  i 1
Comparison of Data Sets:
x  x2
t calculated  1
s pooled
z
n  1
x x
s
x  2s
 x
ts
n
  xi  x1 2   x j  x2 2
n1 n2
n1  n2
s pooled 
Set1
Set 2
n1  n2  2
F Test:
t calculated 
x1  x2
s12
n1

s22
Degreesof freedom 
n2
Comparison of Two Methods:
t calculated 
d
sd
sd 
  2 2
  s1

  n1 

 

 n1  1



Q Test:
 d i  d 
2
n
 s2

s22
 1


 n1
n2 


n  1
Q
Gap
Range
2
 s2

 2

 n2 


n2  1
2








2
[Unknown] from Calibration Curve:
x
yb
m
Chemistry 221 – Final Exam Fall 2006
Standard Addition:
X  f  X i  Vo 
V 
S  f  S i  VS 
V 
page 7
X i
S  f  X  f
Name
Internal Standard:

Ax
A 
 F  S 
 X   S  
IX
I S X
( Vo  Vs )10 E / S  10 k / S Vo c x  10 k / S c sVs
Thermodynamics:
G = H –TS
K e
pX:
 G
o
K(T )  e
RT
Ionic Strength:

pX   log10 [ X ]

 H o
RT
Debye-Hϋckel Equation:
 0.51 z 2 
log  




1   
305 

1
1
c1 z12  c2 z22  K   c i z i2
2
2 i

Fraction Dissociated:

Henderson-Hasselbalch Equation:
 [ A ] 

pH  pK a  log 
 [ HA] 


x
F
Monoprotic Weak Acid:

[H ] 
 Ka 
 [ B] 

pH  pKa  log 
 [ BH  ] 


Diprotic Weak acid:
[H  ] 
K a2  4 ( 1 )( F )( K a )
2
Isoionic point:
K 2 K1 F  K1 K w
K1  F
Triprotic Weak acid:
K 1 K 2 F  K1 K w
K1  F
[H  ] 

Isoelectric point:
pH  2 ( pK1  pK2 )
1
[H  ] 
K 2 K1 F  K1 K w
K1  F
Gran plot:
[H  ] 
K2 K3 F  K2 K w
K2  F
EDTA:

Vb 10  pH  HA K a Ve  Vb 
 A
[Y 4  ]  Y 4  EDTA
K 'f  K f  Y 4-
Electrochemistry:
G   nFE
E cell  E   E 
0.05916 V
[B]b
EE 
log
n
[ A] a
o
K  10
nE o
0.05916
Chemistry 221 – Final Exam Fall 2006
page 8
Redox Indicator:
Spectrophotometry:
0.05916 

E   Eo 
volts
n


E  h  hc / 
Extractions:


V1
qn  

 V1  KV2  
D
P
A   log 
 Po
Name

   log (T ))


A  bc
Chromatography:
n
D
K B Ka

Ka  [ H ]
K HA [ H  ]
t'r  t r  t m

t'r1
( t r2  t r1 )
Rs 
( wb2  wb1 ) / 2
Ka  [ H  ]
t t
k'  r m
tm
t'r 2
2
 t
 tr 
 r


N  16 

5
.
55

 w1
 wb 
 2
B
 C x
x
Area of Gaussian peak  1.064  peak height  w1
H  L/ N
Gas Constant:
8.314472 J/K.mol
Faraday constant:
9.649x104 C/mol
Planck’s constant:
6.626x10-34J-s
H  A
speed of light:
3.0x108 m/s
2




2
Chemistry 221 – Final Exam Fall 2006
page 9
Name
SECTION I (Redox, Spectrophotometry, and Chromatography):
1. (24 points) For the following redox titration of Sn2+ with Tl3+ using a Pt indicator electrode and a
Calomel reference electrode (E=0.241):
What is the observed potential when the titrant volume (V) is:
(a) (4 points) V = ½ Ve
(b) (4 points) V = Ve
(c) (4 points) V = 2Ve
(d) (4 points) What redox indicator would you suggest using for this titration?
(e) (4 points) What happens to the potential if the initial Sn2+ and Tl3+ concentration is
doubled?
(f) (4 points) If the analyte was Sn4+ instead of Sn2+, what would be needed before
titrating with Tl3+?
Chemistry 221 – Final Exam Fall 2006
2.
page 10
Name
(25 points)A new drug candidate yields an absorbance of 0.5 at 550 nm with a 0.01M standard
sample using a path length of 1 cm. A plasma sample from a patient yielded an absorbance of 0.1
after the sample was concentrated by a factor of ten.
a. (5 points) What is the molar absorptivity of the new drug candidate?
b. (5 points) What was the original concentration of the drug in the plasma sample?
c. (5 points) What is the energy of a photon of light absorbed by this drug?
d. (5 points) What is absorbing this photon of light in the drug (what is being promoted to an
excited state)?
e. (5 points) If the absorption of a photon results in a to* transition, what chemical feature
must be present in the drug?
Chemistry 221 – Final Exam Fall 2006
page 11
Name
3. (20 points) Fluorescence and Phosphorescence are relatively rare occurrences because most
excited electronic states relax very rapidly.
a. (5 points) How does a molecule in an excited electronic state commonly relax back to the
ground state?
b. (5 points) Fluorescence occurs when:
c. (5 points) Phosphorescence occurs when:
d. (5 points) Why are fluorescence and phosphorescence emission spectra of lower energy or
higher wavelength compared to their excitation spectra?
4. (11 points) Phenytoin, an antiepileptic drug, has a partition coefficient (K) = 19.5 for an extraction
between water (phase 1) and n-octanol (phase 2). 25 mL of a 1 M solution of Phenytoin in water
is extracted three times with 25 mL of n-octanol. Given that phenytoin is a weak base (pKa = 8.3
for its conjugate acid), what fraction of phenytoin will be extracted at pH 2.0?
Chemistry 221 – Final Exam Fall 2006
page 12
Name
5. (20 points) Given the following HPLC chromatogram using a 25 cm column:
Response
5
Void volume
4
B
3
A
2
C
1
0
0.10 0.15
0.15
0.5 0.70
1.25
Time (min)
-1
0
0.30
2
a. (5 points) What is the resolution between peaks A and B?
b. (5 points) Name one parameter that could be changed to improve the resolution between
peaks A and B?
c. (5 points) What is the number of theoretical plates for peak C?
d. (5 points) What is the height equivalent of a theoretical plate for peak C?
Chemistry 221 – Final Exam Fall 2006
page 13
Name
SECTION II (Review):
6. (5 points) Identify one common mistake in weighing a solid precipitate from a gravimetric
analysis that would result in a systematic error (there are multiple possible answers).
7.
(5 points) Given the following buret and meniscus level (right), a student recorded a
volume of 15.5 mL in her lab notebook. What common mistake is the student making
in reading a volume dispensed by this buret?
8. (10 points) What is the (a) accuracy and (b) precision?
9. (5 points) Given the following general exothermic reaction:
What happens to the equilibrium constant (K) if the sample is heated?
10. (5 points) Given two acids, where acid A has a pKa value of 4.75 and acid B has a pKa of -7.
Which of the two acids is a strong acid?
Chemistry 221 – Final Exam Fall 2006
page 14
Name
11. (10 points) What is (a) end-point and (b) equivalence point?
12. (5 points) If you are calculating the pH of a weak acid and you ignore activity, will your
calculated pH be lower or higher than the measured pH?
13. (5 points) A weak base has a pKa of 8.3. At what pH would this base, combined with its
conjugate acid, make a good buffer?
14. (5 points) A diprotic acid, such as amino acids, exists in three forms: acid form [H2L+], basic form
[L-] and intermediate form [HL]. What is the basic assumption that is made when calculating the
pH of the acid form of the diprotic acid?
15. (10 points) An important component of the procedure for the systematic treatment of equilibrium
is making assumptions to simplify the calculations. A common assumption is to ignore chemical
equations with small equilibrium constants. Why?
Chemistry 221 – Final Exam Fall 2006
page 15
Name
16. (5 points) Why is pH an important consideration in an EDTA titration?
17. (10 points) 14C dating of a fossilized bone was measured twice by two different students. Student
A measured an average age of 15,000 years based on five measurements. Student B measured an
average age of 18,000 years also based on five measurements. The pooled standard deviations for
the two sets of data are 800 years. Are the students’ results significantly different at the 95%
confidence level?
18. (10 points) What is the general pH (acidic, basic, neutral) at the equivalence point for the titration
of a (a) strong acid with a strong base and a (b) weak base with a strong acid.
Chemistry 221 – Final Exam Fall 2006
page 16
Name
19. (10 points) Gravimetric analysis is used to measure the concentration of Ag+ in an unknown
sample by the addition of NaBr.
a. What concentration of NaBr is required so the residual Ag+ concentration is 1x10-10?
b. What happens to the solubility of Ag+ if the unknown sample contains 1M NaCl?