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UV-Visible Spectroscopy Questions and Answers | UV-Visible Spectroscopy MCQs

(1) What is the wavelength range for UV spectrum of light?
[A] 400 nm – 700 nm
[B] 700 nm to 1 mm
[C] 0.01 nm to 10 nm
[D] 10 nm to 400 nm
Answer: 10 nm to 400 nm
(2) Which of the following comparison is correct for solvent shift on the n –>π* transition of acetone?
[A] H20 = CH30H = C2H50H = CHC13 = C6H14
[B] H20 > CH30H > C2H50H > CHC13 > C6H14
[C] H20 < CH30H < C2H50H < CHC13 < C6H14
[D] H20 > CH30H < C2H50H < CHC13 < C6H14
Answer: H20 < CH30H < C2H50H < CHC13 < C6H14

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(3) What is the correct order of λmax for n –> σ* transition?
[A] R-OH > R-NH2 > R-SH
[B] R-OH < R-NH2 < R-SH
[C] R-OH > R-SH > R-NH2
[D] R-OH < R-SH < R-NH2
Answer: R-OH < R-NH2 < R-SH
(4) What is the correct order of λmax for n –> π* transition for the R-CN, R-NO2, and R-N=N-R?
[A] R-CN < R-NO2 < R-N=N-R
[B] R-CN = R-NO2 = R-N=N-R
[C] R-CN > R-NO2 > R-N=N-R
[D] R-CN > R-NO2 < R-N=N-R
Answer: R-CN < R-NO2 < R-N=N-R
(5) What is the correct order of λmax for π –> π* transition for the following three compounds?
[A] R-C=C-R > R2C = CR2 > R-CHO
[B] R-C=C-R < R2C = CR2 < R-CHO
[C] R-C=C-R = R2C = CR2 = R-CHO
[D] R-C=C-R < R2C = CR2 >R-CHO
Answer: R-C=C-R < R2C = CR2 < R-CHO
(6) What is the correct order of λmax for n–> π* transition for the following three compounds?
[A] RCOOH > RCOOR’ > RCONH2
[B] RCOOH = RCOOR’ = RCONH2
[C] RCOOH = RCOOR’ < RCONH2
[D] RCOOH = RCOOR’ > RCONH2
Answer: RCOOH = RCOOR’ = RCONH2
(7) Which of the following is the correct order of λmax for n–> π* transition for the given compounds?

[A] 1>2>3>4>5
[B] 1<2<3<4<5
[C] 1>2<3>4<5
[D] 1>2>3<4>5
Answer: 1>2>3>4>5
(8) The ultraviolet spectrum of benzonitrile shows a primary absorption band at 224 nm. If a solution of benzonitrile in water, with a concentration of 1x 10-4 molar, is examined at a wavelength of 224 nm, the absorbance is determined to be 1.30. The cell length is 1 cm. What is the molar absorptivity of this absorption band?
[A] 2.3 x 104
[B] 3.3 x 104
[C] 1.3 x 104
[D] 4.3 x 104
Answer: 1.3 x 104
(9) The ultraviolet spectrum of benzonitrile shows a secondary absorption band at 271 nm. If a solution of benzonitrile in water, with a concentration of 1×10-4 molar solution is examined at 271 nm, what will be the absorbance reading (ℇ = 1000) and what will be the intensity ratio, IO/I, respectively?
[A] 0.1, 1.26
[B] 0.2, 2.26
[C] 0.3, 3.26
[D] 0.4, 4.26
Answer: 0.1, 1.26
(10) Which of the following structural formula that is consistent with the following observations: An acid, C7H4O2Cl2 shows a UV maximum of 242 nm?

[A] (a)
[B] (b)
[C] (c)
[D] (d)
Answer: (c)

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