250+ TOP MCQs on Identification of Common Plastics and Rubbers and Answers

Polymer Engineering Multiple Choice Questions on “Identification of Common Plastics and Rubbers-1”.

1. A rubber polymer sample A is reacted with chromic acid solution and yields acetic acid solution. Compound A also gives positive Weber test. Which of the following is possibly A?
a) 1,4-polyisoprenes
b) butyl rubber
c) nitrile butadiene rubber
d) all of the mentioned

Answer: a
Clarification: 1,4-polyisoprenes yield acetic acid with chromic acid solution which is identified by its odour. It also gives positive weber test.

2. Which of the following does not give positive weber test of rubbers?
a) natural rubber
b) butyl rubber
c) polyisoprene rubber
d) styrene butadiene rubber

Answer: d
Clarification: In weber test, acetone-extracted polymer is dissolved in carbon tetrachloride with little bromine solution and then heated to remove excess bromine. The residue is then warmed in little phenol. The solution turns violet or purple due to presence of poluisoprenes, and so his test is positive for NR, IR and butyl rubber.

3. Polysulphide rubbers when treated with trichloroacetic acid imparted colour X, which turned to colour Ysolution on boiling and then colour Z precipitate on dilution. Which set of colours represent X, Y, Z, respectively?
a) pink, red-brown, grey
b) pink, ruby-red, rose-pink
c) pink, red-brown, yellow
d) pink, ruby-red, yellow

Answer: b
Clarification: Polusulphide rubbers give pink colour on treatment with trichloroacetic acid which turns ruby-red solution on boiling, giving rose-pink precipitate on dilution.

4. Which of the following rubbers when treated with trichloroacetic acid give pink-mauve melt and on dilution give grey-mauve precipitate?
a) isomerized rubber
b) acetone-extracted NR
c) gutta percha
d) all of the mentioned

Answer: d
Clarification: Acetone-extracted NR, isomerizaed rubber and gutta percha when warmed with trichloroacetic acid give pink-mauve melt and on dilution with water result in grey-mauve precipitate.

5. Which of the following rubber do not respond to trichloroacetic acid?
a) isomerized rubber
b) chlorinated rubber
c) polysulphide rubber
d) butyl rubber

Answer: b
Clarification: Chlorinated rubber does not produce any effect when treated with trichloroacetic acid.

6. A strip of filter paper dissolved in ethereal solution containing p-dimethylamino benzaldehyde and hydroquinone and then moistened with a 30% solution of trichloroacetic acid in isopropanol produces blue-violet colour in the presence of pyrolytic vapours of rubbers A and B. Which of the following pair represent rubbers A and B?
a) natural rubber and butyl rubber
b) styrene butadiene rubber and silicone rubber
c) styrene butadiene rubber and natural rubber
d) natural rubber and nitrile butadiene rubber

Answer: a
Clarification: The pyrolytic vapours of natural rubber and butyl rubber both produce deep-blue or blue-violet colour to the paper.

7. Which of the following rubbers turn the filter paper in ethereal solution containing p-dimethylamino benzaldehyde and hydroquinone and then moistened with a 30% solution of trichloroacetic acid in isopropanol grey with a yellow tinge?
a) natural rubber
b) silicones
c) polychloroprenes
d) butyl rubbers

Answer: c
Clarification: The pyrolytic vapours of polychloroprenes turn the filter paper grey with a yellow tinge.

8. What colour is obtained by the pyrolytic vapours of butyl rubber on the filter paper freshly soaked in a solution obtained by dissolving yellow mercuric oxide in conc. sulphuric acid and water on boiling?
a) bright yellow
b) grey
c) blue
d) brown-yellow

Answer: a
Clarification: Pyrolytic vapours of butyl rubber produce a bright yellow colour on filter paper freshly soaked in a solution obtained by dissolving yellow mercuric oxide in conc. sulphuric acid and water on boiling.

9. Which of the following do not respond to the Molisch test for carbohydrates?
a) cellulose acetate
b) viscose rayon
c) cellulose nitrate
d) none of the mentioned

Answer: c
Clarification: Cellulose acetate and viscose rayon both give purple colour when Molisch test is performed to them. Cellulose nitrate does not respond to this test at all.

10. What colour is obtained when a drop of diphenylamine solution in concentrated sulphuric acid is added to the sample of cellulose nitrate in the absence of other oxidizing agents?
a) deep blue
b) yellow
c) grey
d) red

Answer: a
Clarification: A deep blue colour product is obtained when a drop of diphenylamine solution in concentrated sulphuric acid is added to the sample of cellulose nitrate in the absence of other oxidizing agents.

11. The aqeous extracts of some polymers when tested with chomotropic solution followed by addition of sulphuric acid and then heating to nearly 100 C gave dark violet colour. Which of the following cannot respond to this test?
a) polyvinyl formal
b) polyoxymethylenes
c) urea-formaldehyde resisns
d) polyacrylonitrile

Answer: d
Clarification: The polymers containing or liberating formaldehyde can turn the solution dark violet. Thus, polyacrylonitrile does not respond to this test.

12. What colour is obtained if condensed pyrolyzate of polyacrylonitrile is made alkaline and boiled with ferrous sulphate followed by acidification?
a) ruby-red
b) prussian blue
c) bright blue
d) red-brown

Answer: b
Clarification: Prussian blue precipitate is obtained on the treatment of pyrozylate of polyacrylonitrile.

13. A strip of cupric acid paper, freshly moistened with a dilute solution of benzidine in dilute acetic acid is held in the pyrolytic vapours of polymer A and a bright blue colouration is obtained. Which of the following could be polymer A?
a) polyamide
b) polyacryonitrile
c) butyl rubber
d) polyvinyl formal

Answer: b
Clarification: Pyrolytic vapours of polyacrylonitrile respond to this test and develop bright blue colouration.

14. What colour is obtained when a strip of filter paper soaked in saturated solution of o-nitrobenzaldehyde in dilute NaOH is held over the prylotic vapours of Nylon 6,6?
a) grey
b) black
c) red
d) yellow

Answer: b
Clarification: The pyrolytic vapours of Nylon 6,6 gives mauve-black colour, when a strip of filter paper soaked in saturated solution of o- nitrobenzaldehyde in dilute NaOH is brought near it.

15. Which of the following polymer will not give grey colour when their pyrolytic vapours are tested with a strip of filter paper soaked in saturated solution of o- nitrobenzaldehyde in dilute NaOH?
a) Nylon 6
b) Nylon 66
c) Nylon 12
d) Nylon 11

Answer: b
Clarification: This test is positive only for the polyamides containing diacids other than adipic acid. Nylon 66 contains adipic acid.