CHEMISTRY 241H — SPRING 2026
EXAM 3 —4/14/2026
NAME (Last, First): h 97/ ONYEN:
INSTRUCTIONS:
1.” Write your name and ONYEN in the spaces provided above.
2. Write free responses in pen, multiple-choice/select can be done in pencil.
3. Read each question carefully.
4. For multiple choice questions, do not circle choice — place your letter choice in the
box provided next to the question.
5. For non-multiple-choice questions, SHOW YOUR WORK with correct units and sig
figs. Partial credit based on work shown.
6. Double-check your calculations.
7. ANSWERS MUST BE PLACED IN THE BOXES and must include the CORRECT
UNITS and sig figs.
8. Do not leave any answers blank.
9. Read and sign the honor pledge when, and only when, you finish taking the
exam. '
10. Return all pages when you complete the exam.
11. Relax. You’ve got this.
Honor Pledge: By signing below, I pledge that I have not violated the UNC Honor
Code by receiving or giving unauthorized assistance on this exam. If I do not sign,
then I acknowledge that I was not honorable in taking the exam and understand that
it will simply not be graded, no questions asked.
(Signature) S
, . (24 points) Answer the following questions. Place the letter of your answer in the
box provided next to each multiple-choice question.
(4 points) A 5.96 x 10 M solution of compound A exhibited an absorbance of 0.524
at 238 nm in a 1.00 cm cuvette. A blank solution containing only solvent had an
absorbance of 0.039 at the same wavelength. Find the molar absorptivity (in M em”
1) of Compound A.
A. 8.14x 10> M cm!
1.63x 10°M "' em’! 0.524 -0.079 = ¢ (1.00cm)5,x5" A
mmgaw
6.64 x 10> M cm™!
7.20x 102 M em™!
424x10°M "' em!
4.05x10°M™" em’!
. (4 points) The region of the electromagnetic spectrum best suited to observe only
rotational transitions?
Infrared (IR)
0w
Microwave
X-Ray
Gamma
mmo
uv
Visible
(4 points) A solution of benzene in methanol has a transmittance of 93.0 % in a 1.00
cm cell at a wavelength of 254 nm. Only the benzene absorbs light at this
wavelength, not the methanol. What will the solution’s transmittance be if it is placed
in a 10.00 cm long pathlength cell?
%1% A= ..LOJT-: —~L0§ 0.93
3
TOmMmUOW>
48.4 %
9.3 %
83.7 %
0.6317 e
| oucm
83.0 %
Af)_ ] 0. 00 et
9.8 %
8.3 %
99.3 %
. (4 points) If you double the intensity of the incident light in a fluorescence
experiment, how should the sample’s fluorescence emission intensity change?
A. No Change
B. Doubled
C. Halved
EXAM 3 —4/14/2026
NAME (Last, First): h 97/ ONYEN:
INSTRUCTIONS:
1.” Write your name and ONYEN in the spaces provided above.
2. Write free responses in pen, multiple-choice/select can be done in pencil.
3. Read each question carefully.
4. For multiple choice questions, do not circle choice — place your letter choice in the
box provided next to the question.
5. For non-multiple-choice questions, SHOW YOUR WORK with correct units and sig
figs. Partial credit based on work shown.
6. Double-check your calculations.
7. ANSWERS MUST BE PLACED IN THE BOXES and must include the CORRECT
UNITS and sig figs.
8. Do not leave any answers blank.
9. Read and sign the honor pledge when, and only when, you finish taking the
exam. '
10. Return all pages when you complete the exam.
11. Relax. You’ve got this.
Honor Pledge: By signing below, I pledge that I have not violated the UNC Honor
Code by receiving or giving unauthorized assistance on this exam. If I do not sign,
then I acknowledge that I was not honorable in taking the exam and understand that
it will simply not be graded, no questions asked.
(Signature) S
, . (24 points) Answer the following questions. Place the letter of your answer in the
box provided next to each multiple-choice question.
(4 points) A 5.96 x 10 M solution of compound A exhibited an absorbance of 0.524
at 238 nm in a 1.00 cm cuvette. A blank solution containing only solvent had an
absorbance of 0.039 at the same wavelength. Find the molar absorptivity (in M em”
1) of Compound A.
A. 8.14x 10> M cm!
1.63x 10°M "' em’! 0.524 -0.079 = ¢ (1.00cm)5,x5" A
mmgaw
6.64 x 10> M cm™!
7.20x 102 M em™!
424x10°M "' em!
4.05x10°M™" em’!
. (4 points) The region of the electromagnetic spectrum best suited to observe only
rotational transitions?
Infrared (IR)
0w
Microwave
X-Ray
Gamma
mmo
uv
Visible
(4 points) A solution of benzene in methanol has a transmittance of 93.0 % in a 1.00
cm cell at a wavelength of 254 nm. Only the benzene absorbs light at this
wavelength, not the methanol. What will the solution’s transmittance be if it is placed
in a 10.00 cm long pathlength cell?
%1% A= ..LOJT-: —~L0§ 0.93
3
TOmMmUOW>
48.4 %
9.3 %
83.7 %
0.6317 e
| oucm
83.0 %
Af)_ ] 0. 00 et
9.8 %
8.3 %
99.3 %
. (4 points) If you double the intensity of the incident light in a fluorescence
experiment, how should the sample’s fluorescence emission intensity change?
A. No Change
B. Doubled
C. Halved
