This set of Polymer Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Natural Rubber”.
1. Which tree gives out the latex to obtain natural rubber?
a) eucalyptus
b) hevea brasiliensis
c) anogeissus
d) astragalus
View Answer
Explanation: 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
View Answer
Explanation: 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
View Answer
Explanation: 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
View Answer
Explanation: 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
View Answer
Explanation: 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
View Answer
Explanation: 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
View Answer
Explanation: 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%
View Answer
Explanation: 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
View Answer
Explanation: 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
View Answer
Explanation: 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
View Answer
Explanation: 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
View Answer
Explanation: Hydrochlorinated rubber is conveniently obtained by hydrochlorination with gaseous HCl using rubber in benzene solution.
Sanfoundry Global Education & Learning Series – Polymer Engineering.
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