Organic Chemistry Questions and Answers – Photochemistry | Organic Chemistry Multiple Choice Questions and Answers

Questions
1 The fact that the fluorescence wavelength is often much longer than the irradiation wavelength (Stokes shift) is a consequence of which phenomenon?
A low extinction coefficients (Lambert-Beer law)
B vertical transitions (Kasha’s rule)
C high ISC rates (El Sayed rule)
D the Franck–Condon principle

Answer: the Franck–Condon principle
2 Which of the following is an incorrect statement?
A First step in photochemistry is excited state (photoexcitation)
B Photochemical reactions are caused by absorption of ultraviolet only
C When a molecule or atom in the ground state (S0) absorbs light, one electron is excited to a higher orbital level
D It is possible for the excited state S1 to undergo spin inversion

Answer: Photochemical reactions are caused by absorption of ultraviolet only
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3 Which regions of the light radiations of the visible ultraviolet lying between – wavelength are chiefly concerned in bringing about photochemical reactions?
A 1000 Å and 2000 Å
B 1500 Å and 1000 Å
C 8000 Å and 2000 Å
D 19000 Å and 12,000 Å

Answer: 8000 Å and 2000 Å
4 Which of the following instruments is used to measure the energy of the monochromatic radiation most accurately?
A Photoelectric cell
B Thermopile
C The potential detector
D The chemical actinometer

Answer: Thermopile
5 The molar extinction coefficient of B (MW = 180) is 4 x 103 L mol-1 cm-1. One-liter solution of C which contains 0.1358 g pharmaceutical preparation of B, shows an absorbance of 0.411 in a 1 cm quartz cell. What is the percentage (w/w) of B in the pharmaceutical preparation?
A 10.20
B 13.60
C 20.40
D 29.12

Answer: 13.60
6 What are the appropriate reasons for the deviation from the Beer’s law among the following?

(A) Monochromaticity of light

(B) Very high concentration of analyte

(C) Association of analyte

(D) Dissociation of analyte

A A, B and D
B B, C and D
C A, C and D
D A, B and C

Answer: B, C and D
7 A 0.1 M solution of compound A shows 50% transmittance when a cell of 1 cm width is used at λ1 nm. Another 0.1 M solution of compound B gives the optical density value of 0.1761 using 1cm cell at λ1 nm. What will be the transmittance of a solution that is simultaneously 0.1 M in A and 0.1 M in B using the same cell and at the same wave length? [log 1.301; log 1.4771; log 50 = 1.699].
A 33.3%
B 50%
C 66.7%
D 70%

Answer: 33.3%
8 Which of the following will result in deviation from Beer’s law?

(A) Change in a refractive index of medium

(B) Dissociation of analyte on dilution

(C) Polychromatic light

(D) Path length of cuvette

A A, B and C
B B, C and D
C A, C and D
D A, B and D

Answer: A, B and C
9 The quantum efficiency of a photochemical reaction is defined as _______
A ratio of molecules decomposed in a given time to the number of quanta absorbed in the same time
B number of 11101ecules decomposed in a given time
C number or quanta absorbed percent time
D ratio of’ molecules decomposed in a given time to the number of quanta emitted in the same time

Answer: ratio of molecules decomposed in a given time to the number of quanta absorbed in the same time
10 Which of the following are the reactions in which molecules absorbing light do not themselves react but induce other molecules to react?
A Free radical reactions
B Chain reactions
C Reversible reactions
D Photosensitized reactions

Answer: Photosensitized reactions

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