SMJK YUK KWAN, BATU GAJAH, PERAK.

NATURAL RUBBER

2.9.1 Examples of natural polymers and their monomers.1. What is a polymer? ____________________________________________________2. Polymers can be classified into 2 groups.

Name the 2 groups and give three examples of polymers for each group.(a) ________________(b) ________________

3. What are the monomers for the following polymers?(a) Protein: ______________(b) Carbohydrates: ______________(c) Natural Rubber: ______________

2.9.2 Structural formula of natural rubber.1. Draw the monomer of natural rubber.

What is the IUPAC name for monomer of natural rubber?2. Poly(isoprene), natural rubber is produced by the addition polymerisation of isoprene.

Draw the repeating unit of natural rubber.

2.9.3 Coagulation of latex.1. An experiment is carried out to investigate the coagulation of rubber latex.

3 beakers, A,B and C with the contents as shown in the table below, are left aside for one day.

(a) Complete the table shown below.

Beaker Mixture ObservationA 20 cm3 latex

+ 5 cm3 ethanoic acidB 20 cm3 latex

+ 5 cm3 ammonia solutionC 20 cm3 latex

only (control)

(b) Explain the observation expected in(i) Beaker A:(ii) Beaker B:(iii) Beaker C:

2.9.4 Vulcanisation of rubber; properties and uses of rubber.1. Vulcanised rubber is used in the making of vehicle tyres.

(i) State one method that can be used to vulcanise rubber.(ii) the diagram below shows vulcanised rubber.

Explain the effect of vulcanisation on the structure and properties of rubber.

2. Give 3 uses of natural rubber.

SMK YUK KWAN, BATU GAJAH, PERAK.

Natural Rubber ( Answers )

2.9.11 a polymer is a large, long-chain molecule formed by joining together thousands of

smaller monomer molecules.

2. (a) Natural polymers: proteins, starches, natural rubber(b) Synthetic polymers: poly(ethene), nylon, polyesters.

3. (a) amino acids(b) glucose(c) isoprene

2.9.21.

2-methlybutene-1,3-diene.

2.

2.9.3(a)

Beaker Mixture ObservationA 20 cm3 latex

+ 5 cm3 ethanoic acidCoagulation of latexoccurs rapidly

B 20 cm3 latex+ 5 cm3 ammonia solution

Latex does not coagulate

C 20 cm3 latexonly (control)

Coagulation of latexoccurs slowly

(b) (i) Beaker A-Positively charged H+ ions from the acids neutralise the negatively charged membranes of the colloidal particles. Repelling forces between colloidal particles disappear.-collisions of these neutral particles cause their membranes to break up, rubber polymers are set free.-The free rubber polymers combine together to form large lumps.

(ii) Beaker B-Hydroxide ions, OH- from the aqueous ammonia solution neutralise the lactic acids produced by the bacteria in the latex.-the negatively charged on the membrane of the colloidal particles remain.-the repelling forces between the particles keep them apart.-no coagulation of latex occurs

(iii) Beaker C-Bacteria from the air slowly attack the protein on the membrane of the colloidal particles to produce lactic acids. -ionisation of lactic acids produce hydrogen ions, H+

-H+ ions from the acids neutralize the negatively charged membranes of the colloidal particles. Repelling forces between colloidal particles disappear.-collisions of these neutral particles cause their membranes to break up, rubber polymers are set free.-the free rubber polymers combine together to form large lumps.

2.9.41. (i) heat natural rubber and sulphur with zinc oxide as catalyst.

(ii) -in vulcanisation, sulphur atoms form linkage between long chains of rubber polymers.-the sulphur linkages prevent the long polymers chains from sliding over each other.-this caused the vulcanized rubber stronger and harder.-the sulphur linkage help the long polymers chains to return to their original position after stretching.-this caused the vulcanized rubber more elastic.-the formation of sulphur lingkages reduce the number of carbon-carbon double bonds in the molecules of vulcanized rubber.-vulcanised rubber is also more resistant to heat and oxidation.

2. vehicle tyres, rubber hoses, surgical gloves.