1. What happens to the metal ion when it reacts with peroxide in a bimolecular initiator system?
a) oxidizes
b) reduces
c) no change
d) none of the mentioned
Explanation: The reaction of reducing metal ion and peroxide is given here-
M(m-1)+ + R─O─O─R→ Mm+ +∙OR + OR–.
2. What is the mechanism by which dithionite ion decomposes to give free radical?
a) cleavage of S─O bond
b) cleavage of S─S bond
c) electron transfer
d) cleavage of O─O bond
Explanation: Dithionite ion (S2O42-) undergoes decomposition by the cleavage of S─S bond to give ∙SO2–.
3. What happens to copper ion, when it gives out radicals in acidic medium?
a) oxidizes
b) reduces
c) constant charge
d) none of the mentioned
Explanation: When copper ion reacts in acidic medium, electron transfer takes place from copper to H+ ion, to give a free radical.
For example,
Cu+ + H+ → Cu2+ + H∙.
4. What is the mechanism of uncatalyzed photo-initiation of polymerization, when light of specific wavelength falls on monomer?
a) monomer directly decomposes to give radicals
b) monomer generates excites species by absorbing light quanta and then decompose into radicals by homolysis
c) photo-initiator is added to monomer and decomposes to radicals by photolysis
d) all of the mentioned
Explanation: The monomer, on photo-activation, generates excited species M*, by absorbing the light quanta of specific wavelength and the subsequently decomposes to give radicals by homolysis.
5. What has the terms kd[I] in the overall rate equation of uncatalyzed photo-polymerization been replaced by?
a) intensity of light radiation absorbed
b) intensity of incident light
c) number of pairs of chain radicals formed per quantum of light absorbed
d) monomer concentration
Explanation: The term kd[I] is replaced by the intensity of active radiation absorbed, Ia and f is replaced by φ that stands for number of pairs of chain radicals formed per quantum of light absorbed.
6. What does the intensity of active radiation absorbed in uncatalyzed photo-polymerization, not depend on?
a) thickness of reaction mixture
b) intensity of incident radiation
c) monomer concentration
d) none of the mentioned
Explanation: The intensity of incident light does not vary measurably with the thickness of reaction mixture, while it is proportional to the product of intensity of incident radiation and monomer concentration.
7. How does the overall rate of uncatalyzed photo-polymerization vary, when the monomer concentration is quadrupled, rest all the terms remain same?
a) two fold increase
b) eight fold increase
c) remains same
d) two fold decrease
Explanation: According to the rate expression of uncatalyzed photo-polymerization, we have
Rp α [M]1.5
Therefore, when monomer concentration is quadrupled, Rp increases by 8 times.
8. Which of the following initiator system works on the mechanism of photo-activation?
a) hydrogen halide
b) nitrobenzene complexes
c) hydrogen sulphide
d) oxalate complex of transition metals
Explanation: The cleavage of H─S bond in hydrogen sulphide takes place by photo-activation, which then gives H∙ and HS∙ radicals.
9. Photo-activation allows the use of a wide range of chemicals as polymerization initiators in comparison to the thermal catalyzed process. State true or false.
a) true
b) false
Explanation: This happens because of the high selectivity of photolytic homolysis in most compounds.
10. What is the expression for rate of initiation in catalyzed photo-polymerization? ( I0 and φ are the intensity of incident light and number of pairs of chain radicals formed per quantum of light absorbed, respectively and ε be the molar absorption coefficient )
a) 2φεI0[I]
b) φεI0[M]
c) 2φεI0[M]
d) φεI0[I]
Explanation: The rate of initiation in catalyzed photo-polymerization, when a photo-initiator, I is used, is given by-
Ri = 2φεI0[I].