The CBSE Class 12th Chemistry Examination will be held on March 7, 2020. The students who are appearing for CBSE Class 12th Examination can go through the important questions and answers mentioned in this article. The questions mentioned in this article are based on the previous year question papers, sample papers and NCERT textbook.
Question 1- Draw the structures of the monomers of the following polymers:
Question 2- What is the repeating unit in the condensation polymer obtained by combining HO2CCH2CH2CO2H (succinic acid) and H2NCH2CH2NH2 (ethylenediamine)?
Question 3- Differentiate:
(a) condensation and addition polymerisations
(b) thermoplastic and thermosetting polymers
Answer: (a) In Condensation polymerisation, two or more bifunctional molecules undergo a series of independent condensation reactions with the elimination of simple molecules like H2O, alcohol, NH3, CO2, HCl etc. to form a macromolecule. Example: Formation of nylon 6, 6 while in Addition polymerisation, the molecules of the same or different monomers simply add on one another to form macromolecule. These molecules occur among molecules containing double and triple bonds. Example: Formation of polyethene
(b) Linear polymers in which the intermolecular forces of attraction are in between those of elastomers and fibres and can be melted again and again on heating followed by moulding to give the desired shape is called thermoplastic polymers. Example: Polyethene, Polyvinyl chloride (PVC) etc. whereas Thermosetting polymers are semifluid substances with low molecular masses which when heated in a mould, undergo a change in chemical composition to give a hard, infusible ana an insoluble mass. These cannot be re-melted. Example : Bakelite, Melamine etc.
Question 4-: Draw the structures :
Question 5- Name the monomers used:
(iv) Nylon-6, 6
Answer: (i) Phenol and Formaldehyde
(iii) Ethylene glycol and Terephthalic acid.
(iv) Adipic acid and Hexamethylene diamine.
Question 6- Define:
(ii) Condensation polymers
Answer: (i) Elastomers: These are rubber-like solids with elastic properties. In these elastomeric polymers, the polymer chains are held together by the weakest intermolecular forces. These weak binding forces permit the polymer to be stretched. A few ‘crosslinks’ are introduced in between the chains, which help the polymer to retract to its original position after the force is released as in vulcanised rubber. The examples are buna-S, buna-N, neoprene, etc.
(ii) Condensation polymers: The condensation polymers are formed by repeated condensation reaction between two different bi-functional or tri-functional monomeric units. In these polymerisation reactions, the elimination of small molecules such as water, alcohol, hydrogen chloride, etc. take place. The examples are terylene (dacron), nylon 6, 6, nylon 6, etc. For example, nylon 6, 6 is formed by the condensation of hexamethylene diamine with adipic acid.
These were some of the important questions from previous year question paper, sample papers and the NCERT textbooks. Students can also check other important articles from the links given below: