Multiple choice question for engineering
Set 1
1. The substance that reduces the rate and degree of polymerization, without halting the propagation process, is called a___________
a) retarder
b) inhibitor
c) modifier
d) regulator
Answer
Answer: a [Reason:] Inhibitors consume the radicals and completely suppress the polymerization and brings the rate of polymerization to a zero value.
2. Which of the following has the highest practical utility as an inhibitor?
a) benzoquinone
b) t-butyl catechol
c) nitro benzene
d) DPPH
Answer
Answer: d [Reason:] DPPH (diphenylpicrylhydrazyl) is too stable toact as free radical but it has great potential to react with chain radicals to completely terminate them.
3. What is the order of inhibitor consumption in an inhibition process?
a) first
b) second
c) zero
d) none of the mentioned
Answer
Answer: c [Reason:] In an ideal inhibition process, the consumption rate is independent of inhibitor concentration and depends on the rate of generation of radicals, by any means. The radical generation is however independent of the inhibitor, thus the inhibitor consumption is of zero order.
4. The inhibition period is proportional to the monomer concentration in the system. State true or false.
a) true
b) false
Answer
Answer: b [Reason:] The inhibition period does not depend on monomer concentration; instead, it is proportional to the initial concentration of the inhibitor.
5. What does the stoichiometric ratio and nature of products formed depends on, when the reaction of inhibitor radicals and chain radicals leads to copolymerization?
a) nature of monomer
b) initiator
c) solvent
d) all of the mentioned
Answer
Answer: d [Reason:] The nature of non-radical products formed through reaction of inhibitor radicals and chain radicals, which may even lead to copolymerization, and the stoichiometric ratio, may not follow a uniform pattern which largely depends on the nature of monomer and overall polymerization environment including initiator, solvents, etc.
6. Where has the role of aromatic nitro compounds as an inhibitor or retarder been unsuccessful?
a) styrene polymerization
b) vinyl acetate polymerization
c) acrylate polymerization
d) vinyl chloride polymerization
Answer
Answer: c [Reason:] These compounds have been unsuccessful or ineffective in any of retardation and inhibition, for acrylate polymerization.
7. What happens to the rate of polymerization at the end of inhibition period as compared to the rate for uninhibited monomer, when oxygen is used as an inhibitor?
a) recedes
b) exceeds
c) remains same
d) none of the mentioned
Answer
Answer: b [Reason:] The rate of polymerization usually observed at the end of inhibition period due to oxygen often exceeds that for the uninhibited monomer under otherwise comparable conditions.
8. What is the necessary condition for hydroquinone to be used as inhibitors?
a) presence of α-hydrogen
b) presence of oxygen
c) presence of ring
d) none of the mentioned
Answer
Answer: b [Reason:] The inhibitory action of hydroquinone is noticeable only in the presence of oxygen, as it become effective due to its oxidation to quinones.
9. What role does nitrobenzene play for the polymerization of methyl acrylate?
a) inhibitor
b) retarder
c) chain transfer agent
d) none of the mentioned
Answer
Answer: c [Reason:] The value of inhibitor constants for a particular substrate widely depends on the reactivity of chain radicals. Nitrobenzene acts as a strong chain transfer agent for polymerization of methyl acrylate due to the less reactivity of methyl acrylate radicals.
Set 2
1. Which of the following is a mode for radicals to move out of the cage in decomposition mechanism of initiator?
a) net diffusion of radicals produced
b) release of a small molecule, formed by decomposition of radicals, followed by diffusion
c) all of the mentioned
d) none of the mentioned
Answer
Answer: c [Reason:] The radicals may undergo a net diffusion through the cage, having walls of solvent molecules, or a release of small molecule, through decomposition of one or both the radicals, is accompanied with the diffusion out of solvent cage.
2. Which of the following factors does initiator efficiency depend on?
a) initiator molecules
b) polymerization condition
c) solvent
d) all of the mentioned
Answer
Answer: d [Reason:] The initiator efficiency not only depends on initiator molecules but is also affected by condition of polymerization and the solvent used.
3. How is the rate constant ratio kx/kD related to initiator efficiency?
a) kx/kD = (1-f)/f
b) kx/kD = f/(1-f)
c) kx/kD = 1/(1-f)
d) kx/kD = (1-f)/2f
Answer
Answer: a [Reason:] The relationship between the ratio kx/kD and initiator efficiency, f is given by-
kx/kD = (1-f)/f.
4. Which of the following is required for determination of initiator efficiency, when the approach involves measurement and conversion of polymer production and initiator decomposition?
a) number of polymer molecules formed
b) number of radicals produced
c) mode of termination
d) all of the mentioned
Answer
Answer: d [Reason:] For determining f, number of polymers molecules formed and number of radicals produced over same period of time, are compared. Along with this, the mode of termination should also be known as it decides how many initiator fragments are trapped as end groups per polymer molecule.
5. When should the measurement of the initiator decomposition be done?
a) before polymerization
b) after polymerization
c) during polymerization
d) independent of time
Answer
Answer: c [Reason:] The measurement of initiator decomposition is done during actual polymerization, as an independent measurement in the absence of monomer would lead to errors.
6. Which is the most useful approach for evaluating initiator efficiency?
a) analysis of initiator fragments in polymer formed and comparing to initiator consumed
b) measurement and comparison of polymer production and initiator decomposition
c) use of inhibitors
d) dead-end-effect in polymerization
Answer
Answer: d [Reason:] This technique allows treating the kinetic data obtained under dead-end conditions to evaluate both kd, the rate constant of initiator decomposition reaction and f, the initiator efficiency, which is most useful of all the approaches.
7. What is the mechanism of radical generation by bimolecular initiating systems?
a) electron or charge transfer
b) cleavage of bonds
c) catalyzation
d) all of the mentioned
Answer
Answer: a [Reason:] Bimolecular initiation systems mostly generate radicals through electron transfer mechanism or via formation of complexes of different degrees of heat or light stability, through charge transfer mechanism.
8. What is the color of the non-radical adduct formed, when the inhibitor diphenylpicrylhydrazyl reacts with other radicals?
a) deep violet
b) light brown yellow
c) dark red
d) black
Answer
Answer: b [Reason:] The most widely used inhibitor, diphenylpicrylhydrazyl, when reacts with other radicals give a non-radical adduct of light brown yellow color.
9. What has the initiator concentration in the expression for Rp, in bimolecular initiation system, been replaced by?
a) reducing agent concentration
b) oxidising agent concentration
c) product of oxidizing and reducing agent concentration
d) no change
Answer
Answer: c [Reason:] The initiator concentration in the expression has been substituted by product of oxidizing and reducing agent concentration, and the system is commonly known as redox initiator systems.
10. What is the radical produced in the decomposition of acetyl peroxide?
a) ∙CH3
b) ∙C2H5
c) CO2
d) None of the mentioned
Answer
Answer: a [Reason:] The reaction is given by-
CH3─C(O)─O─O─C(O)─CH3 → 2CH3─C(O)─∙O → 2∙CH3 + 2CO2.
11. Which molecule is released when AIBN is decomposed to give free radicals?
a) N2
b) HCN
c) NH3
d) None of the mentioned
Answer
Answer: a [Reason:] The reaction is given by-
(CH3)2─C(CN) ─N═N─(CH3)2─C(CN)→ (CH3)2─C(CN)─N═N∙ + (CH3)2─∙C─CN → 2(CH3)2─∙C─CN + N2.
12. What is the radical produced by decomposition of persulfate ion?
a) S∙O4–
b) SO3∙
c) SO2
d) None of the mentioned
Answer
Answer: a [Reason:] The decomposition reaction of persulfate ion is given by-
─O3S─O─O─SO3– → 2 S∙O4–.
13. 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
Answer
Answer: a [Reason:] The reaction of reducing metal ion and peroxide is given here-
M(m-1)+ + R─O─O─R→ Mm+ +∙OR + OR–.
14. 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
Answer
Answer: b [Reason:] Dithionite ion (S2O42-) undergoes decomposition by the cleavage of S─S bond to give ∙SO2–.
15. 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
Answer
Answer: a [Reason:] 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∙.
Set 3
1. What is the order of a self-catalyzed polyesterification reaction?
a) 2
b) 3
c) 1
d) 4
Answer
Answer: b [Reason:] For each step of reaction between a –COOH group and –OH group, a second functional group –COOH acts as a catalyst in the reaction. Therefore, the reaction follows the third order kinetics.
2. How is the reactivity of a specific functional group, in general, dependent on the size of the molecule to which it is attached, in a polycondensation reaction?
a) increases with increase in molecular size
b) decreases with decrease in molecular size
c) independent of molecular size
d) cannot be determined
Answer
Answer: c [Reason:] The reactivity of functional is independent of the size of the molecule to which it is attached.
3. Which of the following is true about polymer systems in polycondensation?
a) have higher viscosity than small non-polymeric molecules
b) insoluble beyond a critical molecular weight
c) all of the mentioned
d) none of the mentioned
Answer
Answer: c [Reason:] The medium viscosity in polymer systems is much higher than the systems of small non-polymeric molecules. Besides, there tend to become insoluble after a certain range of chain length or molecular weight.
4. Which order kinetics does a strong acid catalyzed polyesterification reaction follow?
a) 1
b) 2
c) 3
d) 4
Answer
Answer: b [Reason:] This reaction is achieved by addition of a strong acid catalyst, which is not utilized in the reaction as in self catalyzed reaction. So, the reaction clearly, follows second order kinetics.
5. What is the slope of the line plotted between square of the average degree of polymerization and time for a self catalyzed polyesterification?
a) 2c02k
b) 2c0k
c) c0k/2
d) c02k
Answer
Answer: a [Reason:] The rate of disappearance of carboxyl groups is given by, -dc/dt = kc3 (due to self catalyzation, second COOH group acts as catalyst, and reaction follows third order kinetics)
On integration we get,
2kt = 1/c2 – constant
On substituting c=c0(1-p), we get
2c02kt = 1/(1-p)2 – constant
This equation gives the slope equal to 2c02k.
6. What factors may be responsible for deviation in the high conversion region of self-catalyzed polycondensation?
a) loss of reactants
b) cyclization
c) other side reactions
d) all of the mentioned
Answer
Answer: d [Reason:] The deviation from linearity in the high conversion region may have arisen due to the factors including loss of reactants, cyclization or other side reactions.
7. What is true about an end functional group, having a terminal reactive centre, of a polymer molecule?
a) has a greater mobility than the polymer molecule as a whole
b) has a lower mobility than the polymer molecule as a whole
c) same as polymer molecule
d) cannot be determined
Answer
Answer: a [Reason:] The functional group at a free end has a good degree of mobility to collide and faster reaction to take place.
8. How does the reaction rate vary with increasing extent of reaction beyond 94% conversion in self catalyzed reaction?
a) decreases
b) increases
c) remains same
d) none of the mentioned
Answer
Answer: a [Reason:] The reaction rate decreases with increasing extent of reaction beyond 94%. The factors responsible are loss of reactants, difficulty in removal of byproduct molecule due to high viscosity and other side reactions.
9. What is the average degree of polymerization for a complete polycondensation reaction in a bifunctional system?
a) infinity
b) 0
c) 1
d) none of the mentioned
Answer
Answer: a [Reason:] For a bifunctional system, average functionality, f=2 and for a complete reaction, extent of reaction, p=1. So the expression for extent of reaction reduces to,
p = [1-(1/Xn)]
where, Xn is the average degree of polymerization. Therefore, Xn=∞. Although it is possible only in hypothetical situation.
10. How is the extent of reaction, p, of a polycondensation reaction related to the average functionality, f, of the system?
a) proportional to f
b) proportional to 1/f
c) proportional to f2
d) proportional to 1/f2
Answer
Answer: b [Reason:] The term for extent of reaction is given by,
p = (2/f)[1-(1/Xn)]
Therefore, it is inversely proportional to f.
11. The average functionality of a polyfunctional system is 2.4. What will be the average degree of polymerization for 80% completion of reaction?
a) 20.55
b) 27.67
c) 50.3
d) 2.97
Answer
Answer: b [Reason:] Using the formula,
p = (2/f)[1-(1/Xn)]
and putting the values of f=2.4 and p=0.8, we get the value of Xn as 27.67.
Set 4
1. How is the average lifetime of a growing radical, under steady state, in a radical polymerization, defined?
a) ratio of the steady state radical concentration and the rate of its termination
b) ratio of termination of the radical and its steady state concentration
c) ratio of steady state radical concentration and the rate of propagation
d) cannot be determined
Answer
Answer: a [Reason:] The average lifetime of a growing radical under steady state is given by the ratio of the steady state radical concentration and the rate of its termination, and is expressed as-
τs = kp[M]/2kt[Rp]s.
2. What is the intensity received by the system in rotating sector technique, under the limiting case of very fast flashing?
a) I0
b) I0/2
c) 2I0
d) 3I0
Answer
Answer: b [Reason:] Under the limiting case of very fast flashing so as to have a little fluctuation in the radical concentration, only 50% of the irradiation is received by the system i.e. continuous illumination of intensity I0/2 is obtained.
3. Which of the following cannot affect the average lifetime of a radical in a photo-initiated polymerization?
a) rate of polymerization, Rp
b) frequency of light radiations
c) intensity of light radiations
d) none of the mentioned
Answer
Answer: d [Reason:] The average lifetime of the radical is proportional to the rate of polymerization, which on the other hand is dependent on frequency and intensity of incident light. Thus the average lifetime can get affected by all the given factors.
4. What is the proportionality order for the average rate of polymerization for steady conditions and continuous illumination, with respect to intensity of illumination?
a) ½
b) 1
c) -½
d) -1
Answer
Answer: a [Reason:] For steady state conditions and continuous illumination,(Rp)s α (I0)1/2.
5. Which of the following is correct regarding the proportionality of average rate for intensity of illumination, if there is very fast blinking with equal light and dark periods?
a) ( Rp) α ½ (I0)1/2
b) ( Rp) α (I0/2)1/2
c) ( Rp) α (I0)1/2
d) ( Rp) α 2(I0)1/2
Answer
Answer: b [Reason:] For very fast blinking with equal light and dark periods, the average rate shows following proportionality for intensity of illumination, (Rp) α (I0/2)1/2.
6. What is the relative rate of polymerization, under steady conditions to that of slow blinking, when the dark period is 4 times longer than the light period?
a) 1/4
b) 1/5
c) 1/51/2
d) 1/2
Answer
Answer: b [Reason:] The relative rate for the slow blinking condition is given by,(Rp)s/(Rp) = 1/(r+1), where r is ratio of dark period to the light one. Thus, the relative rate is obtained as 1/5.
7. How many times is the lighter period shorter than the darker one, if the steady state rate is one third of the average rate for very fast blinking?
a) 4
b) 8
c) 2
d) 3
Answer
Answer: b [Reason:] If the steady state rate is one third of the average rate for very fast blinking, then (Rp)s/(Rp)= 1/3, and for fast blinking
(Rp)s/(Rp)= 1/(r+1)1/2
1/3 = 1/(r+1)1/2
r=8.
Set 5
1. Which tree gives out the latex to obtain natural rubber?
a) eucalyptus
b) hevea brasiliensis
c) anogeissus
d) astragalus
Answer
Answer: b [Reason:] Hevea tree produces a milk-white latex that contains the natural rubber hydrocarbon present in the form of fine emulsion in an aqueous serum which is then later processed to give natural rubber.
2. Which substance is added to the dilute latex to prevent darkening of latex?
a) sodium bisulfite
b) potassium sulfite
c) sodium sulfate
d) potassium sulfate
Answer
Answer: a [Reason:] A little amount of sodium bisulfite is added to the dilute latex before tapping to prevent darkening or discoloration of the latex which may otherwise develop as a consequence of an enzymatic reaction in the latex involving its phenolic constituents producing the dark coloured pigment melanin.
3. Which component has the maximum composition in the Hevea rubber latex?
a) rubber hydrocarbon
b) water
c) proteins
d) sugars
Answer
Answer: b [Reason:] Hevea latex consist of 55-65 % of water, 30-40% of rubber hydrocarbon while proteins and sugars are present in little amount.
4. Which of the following represents natural rubber chemically?
a) cis 1,4-polyisoprene
b) trans 1,4-polyisoprene
c) cis 1,3-polyisoprene
d) trans 1,3-polyisoprene
Answer
Answer: a [Reason:] Natural rubber is chemically known by cis 1,4-polyisoprene. This structure of natural rubber was confirmed by identifying the products derived from its ozonolysis.
5. Consider the following statements about hydrocarbons of natural rubber and gutta percha.
I. They have same elementary formula.
II. They have same molecular weight.
III. Rubber hydrocarbon has low specific gravity than gutta percha.
Which of the following statements are true?
a) I, III
b) I, II, III
c) II, III
d) I only
Answer
Answer: a [Reason:] The hydrocarbons of natural rubber and gutta percha are the same in elementary formula and in their products of ozonolysis. Gutta percha has a lower molecular weight than natural rubber and so natural rubber is less dense than gutta percha.
6. What are the sequential processes through which rubber latex undergo to give natural rubber?
a) tapping-preservation-coagulation
b) preservation-tapping-coagulation
c) tapping-coagulation-preservation
d) coagulation-tapping-preservation
Answer
Answer: a [Reason:] The rubber latex from hevea tree firstly undergoes tapping, then it is preserved using a preservative like sodium pentachlorophenate followed by coagulation using acetic acid o formic acid.
7. What are the temperature and pressure conditions when natural rubber is hydrogenated in the presence of nickel catalyst?
a) 5-10 atm and 180-200 ᵒC
b) 15-20 atm and 180-200 ᵒC
c) 30-35 atm and 100-120 ᵒC
d) 15-20 atm and 100-120 ᵒC
Answer
Answer: b [Reason:] The hydrogenation of rubber can be conveniently done by taking solutions of rubber in 2-3% of cyclohexane using hydrogen at a pressure of 15-20 atm and 180-20 ᵒC and employing nickel catalyst.
8. How much would the unsaturation of cyclized rubber reduce to its original when it forms polycyclic structure?
a) 57-60%
b) 20-30%
c) 40%
d) 70%
Answer
Answer: b [Reason:] Cyclization reaction of rubber leading to the formation of bi- or even polycyclic structures result in the reduction in unsaturation to 20-30% of the original rubber, while the formation of monocyclic structure lead to the drop in unsaturation by 57% of original.
9. What kind of product is obtained on chlorination of natural rubber?
a) elastomer
b) thermoplastic
c) resinous
d) none of the mentioned
Answer
Answer: c [Reason:] The chlorinated rubber formed by chlorination of natural rubber is resinous in character while natural rubber is elastomeric in nature.
10. Which solvent is used to dissolve rubber pieces in the process of chlorination of natural rubber?
a) carbon tetrachloride
b) acetone
c) benzene
d) toluene
Answer
Answer: a [Reason:] In the process of chlorination, rubber small pieces of rubber are dissolved in carbon tetrachloride in presence of a small amount of benzoyl peroxide which act as a depolymerizing agent and lowers the solution viscosity.
11. Which of the following information about chlorinated rubber is wrong?
a) it resists concentrated nitric acid
b) it is used as heat sealable package for dry food
c) it has flame retardant characteristics
d) it is resinous in character
Answer
Answer: b [Reason:] Hydrochlorinated rubber is used as heat sealable package for dry foods whereas chlorinated rubber is used in formulation of paints, lacquers, adhesives and printing inks.
12. Which solution is used for hydrochlorination of natural rubber with HCl gas?
a) benzene
b) toluene
c) carbon tetrachloride
d) acetone
Answer
Answer: a [Reason:] Hydrochlorinated rubber is conveniently obtained by hydrochlorination with gaseous HCl using rubber in benzene solution.
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