Engineering Chemistry MCQ (Silicones and Polymeric Composites)

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Engineering Chemistry MCQ (Silicones and Polymeric Composites)

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Silicones and Polymeric Composites

1. Silicones are called inorganic polymers due to absence of _________________in the main backbone chain.
a) Nitrogen atom
b) Oxygen atom
c) Carbon atom
d) Hydrogen atom
Answer: c
Explanation: Silicones are called inorganic polymers due to the absence of carbon
atoms in the main backbone chain. Carbon compounds are the basis of organic chemistry.

2. Silicones resemble inorganic polymers in having high % of ____________
a) Ionic character of Si-O bond
b) Organic groups on silicon atoms
c) Controlled hydrolysis
d) Solubility
Answer: a
Explanation: Silicones resemble inorganic polymers in having high % of ionic
character of Si-O bond. The bond between silicon and oxygen molecule is very ionic in nature.

3. The catalyst used in the preparation of poly-siloxanes is ____________
a) Benzoyl peroxide
b) Grignard reagent
c) Cumene hydroperoxide
d) Lewis acid
Answer: b
Explanation: The catalyst used in the preparation of poly-siloxanes is Grignard
reagent. The Grignard reaction is an organometallic chemical reaction in which alkyl,
vinyl, or aryl-magnesium halides, CH3MgI (Grignard reagents) add to a carbonyl group in an aldehyde or ketone.

4. Which of the following is tri-functional?
a) Dimethyl silicon chloride
b) Trimethyl silicon chloride
c) Tetramethyl silicon chloride
d) Momethyl silicon chloride
Answer: d
Explanation: Momethyl silicon chloride is tri-functional and gives cross-linking to the final polymer.

5. Which of the following gives linear chain silicones on polymerisation by controlled hydrolysis?
a) Dimethyl silicon chloride
b) Trimethyl silicon chloride
c) Tetramethyl silicon chloride
d) Momethyl silicon chloride
Answer: a
Explanation: Dimethyl silicon chloride gives linear chain silicones on polymerisation
by controlled hydrolysis. All the other options does not give such type of reaction.

6. Which of the following is mono-functional?
a) Dimethyl silicon chloride
b) Trimethyl silicon chloride
c) Tetramethyl silicon chloride
d) Momethyl silicon chloride
Answer: b
Explanation: Trimethyl silicon chloride is mono-functional and hence, a chainstopper.

7. The proportion of momethyl silicon chloride determines the amount of crosslinking that can be obtained in polymerisation.
a) True
b) False
Answer: a
Explanation: The proportion of momethyl silicon chloride used in polymerisation
determines the amount of cross-linking that can be obtained. It is made on an
industrial scale as the principal precursor to dimethyl silicone and polysilane compounds.

8. On increasing the temperature, the viscosity of polysiloxanes ____________
a) Increases
b) Decreases
c) Remain constant
d) First increases then decrease
Answer: c
Explanation: The viscosity of polysiloxanes does not change appreciably with a change in temperature.

9. The bond energy of Si-O bond is ____________
a) 37 kJ/mol
b) 115 kJ/mol
c) 248 kJ/mol
d) 502 kJ/mol
Answer: d
Explanation: The bond energy of Si-O bond is 502kJ/mol. The bond energy is a
measure of the amount of energy needed to break apart one mole of covalently
bonded gases and Si-O bond is very strong.

10. Silicones have good electrical insulation because they are less stable to heat than organic polymers.
a) True
b) False
Answer: b
Explanation: Silicones have good electrical insulation because they are more stable to heat than organic polymers.